decline in late autumn and daily feeding rates average Catfishes 427
less than 30 kg feed/ha during midwinter, although feed
allowances may be higher during abnormally mild win- naturally by certain species of cyanobacteria (Tucker,
ters. Of course, feed allowances vary depending on fish 2000). Off‐flavours are common in pond‐raised catfish
biomass and fish health. In fact, sudden changes in feed- and all fish are ‘taste‐tested’ before scheduling pond har-
ing activity are an important indicator of the general vest to prevent off‐flavoured fish from reaching the
health of fish and reduced feeding activity is often the marketplace.
first sign of an infectious disease outbreak. Most grow‐
out ponds are drained only for purposes of pond renova- Management of off‐flavours relies upon elimination of
tion. Commercial ponds may remain in production for the odorous compound from the flesh to improve fla-
3–20 yr between pond renovations, with an average lifes- vour quality once the organism producing the compound
pan of about 8 yr. is no longer present. Fish with off‐flavours are often are
simply left in the culture pond until the odour‐producing
19.3.2.6 Water Quality Management cyanobacteria disappear from the plankton community.
Channel and hybrid catfish ponds in the USA are oper- More commonly farmers treat ponds with approved
ated without water exchange, except during periods of algicides to eliminate the odour‐producing algae. Fish
excessive rainfall. Availability of dissolved oxygen and flavour quality rapidly improves after the source of the
development of environmentally derived ‘off‐flavours’ odorous compound is eliminated.
are major factors affecting production of channel catfish
in static‐water ponds. Nitrite occasionally accumulates in channel catfish
pond waters and poses a threat to fish health. In south‐
Ponds are not continuously aerated but rather aeration eastern USA, episodes of elevated nitrite levels are most
is initiated (during darkness) when dissolved oxygen common in the spring and fall. Chloride competes with
concentrations fall to a level considered critical by the nitrite for uptake at the gills and prevents nitrite toxico-
individual farmer (usually around 3–4 mg/L) and contin- sis in channel and hybrid catfish. Nitrite toxicosis is eas-
ues until measurements indicate that dissolved oxygen ily prevented by adding common salt (NaCl) to water to
concentrations are increasing as a result of photosynthe- maintain a ratio of 20 mg/L of chloride for every 1 mg/L
sis during daylight. The need for aeration depends on of nitrite‐N.
water temperature, fish biomass and phytoplankton
abundance. Aeration is rare in the first few weeks of the 19.3.3 Nutrition and Feeds
fingerling nursery phase but increases to 6–8 hr, or Feed cost is the largest cost of producing channel catfish,
longer, each night during warm weather in ponds with accounting for about half of the total cost input. Efficient
high fish biomass and abundant phytoplankton. Rates of and economic feeds, together with effective feeding
photosynthesis and respiration decrease as water tem- practices, are therefore essential in catfish farming.
peratures decrease: problems with low dissolved oxygen
are rare in channel catfish ponds when water tempera- Forty nutrients have been identified as essential for nor-
tures fall below 15 °C and most farmers discontinue dis- mal physiological function of channel catfish. The qualita-
solved oxygen monitoring when water temperatures are tive nutritional requirements of channel catfish are similar
expected to remain below that value. to those of other animals, but the absolute and relative
amounts of those nutrients needed by catfish may differ
Paddlewheel aerators (Figs. 3.13 and 4.9) are the most from those needed by other animals. Also, nutrient
common type of aerator used in channel catfish ponds. requirements for channel catfish may vary with fish size,
Most paddlewheel aerators are powered by an electric growth rate, water temperature, diet formulation and other
motor (typically 7.5 kW) and are mounted on floats and factors. Many of those interrelationships are poorly under-
anchored to the pond bank. Aeration in conventional stood. Nutrient levels recommended for channel catfish
ponds is provided at ~2–4 kW/ha; for instance, two or grow‐out feeds are shown in Table 19.2. These require-
three 7.5 kW aerators may be placed in a 6–ha pond. At ments are also presumed to apply to hybrid catfish.
least twice that amount of aeration is provided in inten-
sive pond systems. The range of dietary protein levels in Table 19.2 has been
found adequate for grow‐out of fingerlings to marketable
Objectionable ‘off‐flavours’ in processed channel cat- fish. Generally, the dietary protein level is higher in feeds
fish may be caused by feed ingredients, post‐processing used for smaller fish: recommended levels are 40–50% of
rancidity or odorous compounds absorbed from the diet for fry and 32–35% for small fingerlings. Also, the vita-
environment. The most common off‐flavours described min and mineral requirements for channel catfish were
from pond‐grown channel and hybrid catfish are attrib- determined in aquarium studies using small, rapidly grow-
uted to geosmin and 2‐methylisoborneol, which are two ing fish and may not accurately reflect the requirement for
non‐toxic, earthy‐musty smelling metabolites produced older, slower‐growing fish. Furthermore, catfish ponds are
fertile ecosystems with abundant natural food organisms
that provide some nutriments to the catfish diet.
428 Aquaculture p remixes are added to all channel catfish feeds to ensure
Table 19.2 Recommended nutrient levels for extrusion‐processed nutritional adequacy. Examples of formulations for practical
channel catfish (Ictalurus punctatus) grow‐out feeds. channel catfish feeds are shown in Table 19.3.
Nutrient Recommend level 19.3.4 Infectious Diseases
Protein 26–32% of diet Infectious diseases played a minor role in fish losses on
Lysine 5.1% of dietary protein catfish farms prior to 1980 because low‐intensity man-
Methionine* 2.3% of dietary protein agement practices generally resulted in good pond water
Digestible energy 8.5–9.5 kcal/g protein quality and low disease incidence. Lower fish densities
Lipid 4–6% of diet also reduced transmission of disease organisms within
Carbohydrate 25–35% of diet fish populations. Over the years, stocking and feeding
Vitamins rates steadily increased and infectious diseases emerged
2.5 mg/kg of diet as an important factor in catfish production. Disease
Thiamine 6 mg/kg of diet outbreaks are not uncommon even on well‐m anaged
Riboflavin 5 mg/kg of diet farms.
Pyridoxine 15 mg/kg of diet
Pantothenic acid None Economic losses resulting from infectious diseases are
Nicotenic acid 2.2 mg/kg of diet difficult to quantify because recordkeeping varies among
Folic acid 0.01 mg/kg of diet farmers and many diseases go unreported. In addition,
B12 50–100 mg/kg of diet infectious diseases influence profitability by increasing
Ascorbic acid 2200 IU/kg diet treatment costs, reducing food consumption by fish,
A 1100 IU/kg diet increasing feed conversion ratios, and causing harvest-
D3 30 mg/kg of diet ing delays. Fish‐eating birds may also be attracted to
E 4.4 mg/kg of diet ponds with sick and dying fish causing further losses.
K Survival in the nursery phase (fry to fingerling) averages
Minerals 0.3–0.35% of diet about 65% across the industry, but ranges from less than
Available phosphorus 0.05 mg/kg of diet 10% to more than 90% in individual nursery ponds.
Cobalt 200 mg/kg of diet Primary causes of loss include infectious disease and
Zinc 0.1 mg/kg of diet bird predation. The two most important diseases are the
Selenium 25 mg/kg of diet bacterial diseases ESC and columnaris. Other diseases
Manganese 2.4 mg/kg of diet of fingerling catfish are channel catfish virus disease
Iodine 30 mg/kg of diet (CCVD) and infestations by various metazoan and pro-
Iron 5 mg/kg of diet tozoan parasites, including Ichthyophthirius multifilis,
Copper the ubiquitous white‐spot disease of freshwater fishes.
Hybrid catfish fry‐to‐fingerling survival is better than for
Source: Adapted from Li et al. (2004). channel catfish because hybrids are more resistant to
*Cysteine can replace 60% of the methionine requirement. ESC and CCVD.
Feeds for fry are prepared as meals or flours of small Survival during grow‐out is more difficult to estimate
particle size (< 0.5 mm). They are formulated to contain than for fingerlings because most grow‐out ponds are
high dietary protein levels and high levels of fishmeal. not drained between harvests, making it difficult to
Most feeds for fingerlings and grow‐out fish are prepared maintain accurate inventory records. Experience indicates
by extrusion cooking and drying. That process produces that channel catfish survival during grow‐out may aver-
a hard expanded pellet that floats in water. Extruded age between 60% and 80%. As with fingerlings, survival
feeds must contain ~25% corn or other high‐carbohy- among individual pond populations is highly variable.
drate grains for proper gelatinisation and expansion of Farmers reported that bird predation, the bacterial
pellets during extrusion. Soybean meal provides most of diseases ESC and columnaris, and wintertime fungal
the protein in fingerling and grow‐out feeds. Small infections are responsible for most losses from grow‐out
amounts of fishmeal or other animal protein may be ponds. Other important diseases during grow‐out
added to improve amino acid balance and enhance include the trematode Bolbophorus damnificus and pro-
palatability. Commercial trace mineral and vitamin liferative gill disease (PGD) caused by the myxozoan
parasite, Hennyguya ictaluri. Hybrid catfish are relatively
resistant to ESC, columnaris and PGD, and survival dur-
ing grow‐out usually exceeds 85%.
Assuming 70% survival of fry to fingerlings and 75%
survival from fingerling to harvest, survival over the
Catfishes 429
Table 19.3 Examples of practical catfish feed formulations. Two examples of grow‐out feeds with different crude protein and fishmeal
levels are shown. Values in parentheses are feed crude protein levels.
Feed type
Ingredient Fry Fingerlings Grow‐out Grow‐out
(50%) (35%) (28%) (32%)
Fishmeal (menhaden) 75 8 – 4
Soybean meal – 44 35.5 42
Cottonseed meal – 10 10 10
Corn grain – 28 32 32
Wheat middlings 20 7.5 20 10
Dicalcium phosphate – 0.5 1.0 0.5
Oil or fat 5 2.0 1.5 1.5
Mineral/vitamin premix Include Include Include Include
Source: Adapted from Robinson et al. (2004).
entire production cycle (discounting losses from egg to pond, the ends of the seine are brought together, and the
swim‐up fry in the hatchery) averages just over 50% for seine is gathered onto the seine reel. As the seine is
channel catfish. If 85% of hybrids survive each phase, spooled onto the seine reel, the crowded fish flow into
overall survival exceeds 70%. The superior disease resist- the ‘live car,’ which is a large, open‐topped mesh bag. The
ance of hybrids and the resulting higher survival are the live car is detached from the seine and closed after it is filled
primary advantages of hybrids over channel catfish. with fish. The live car is made of mesh with o penings
sized to retain fish of a certain minimum size (usually
Bacterial diseases are treated using medicated feeds. about 0.5 kg). Fish are allowed to grade by size for several
Three antibiotics are legal to use in the USA: florfenicol, hours. After grading is complete, the larger fish that are
oxytetracyline, and a potentiated sulphonamide contain- retained in the live car are loaded onto transport trucks.
ing sulfadimethoxine and ormetoprim. Florfenicol is The live car is positioned near the bank and fish are
available only by prescription from a veterinarian. scooped into a loading net attached to a hydraulic boom
Vaccine development also has been an active area of (Figure 19.11). In‐line scales record the harvest weight.
research, and a new feed‐delivered ESC vaccine shows
great promise in reducing losses to that disease (Wise Although hybrids are easier than channel catfish to
et al., 2015). External protozoan parasites can be treated capture by seining, they do not grade efficiently through
with chemicals, such as copper sulphate or potassium standard netting. Hybrids have a smaller head and deep
permanganate, applied to the water. At present there is body that cause a significant percentage of fish being
no treatment for PGD, which has a two‐phase life cycle ‘gilled’ (gill‐netted) during grading, resulting in fish
involving a benthic oligochaete and catfish as hosts. death and increased labour to remove gilled fish during
Hybrid catfish appear to be more resistant to infection harvest. To avoid issues with passive grading, most
than channel catfish. hybrid farmers use either a single‐batch production sys-
tem (which does not require fish size grading) or they
19.3.5 Harvesting and Processing grade hybrids with a special live car that contains long
After fish reach the desired market size, they are har- sections of vertical plastic bar graders sewn into the
vested, transported to the processing plant, and pro- netting.
cessed. These practices are relatively standardised across
the channel catfish industry. 19.3.5.2 Processing
Fish are transported alive to processing plants. At the
19.3.5.1 Harvesting processing plant, a sample of fish from the transport
Harvesting catfish is simple because most ponds have truck is tested for flavour quality. If fish are of accept-
regular shapes (usually rectangular) and are shallow with able quality, they are unloaded into large concrete
smooth bottoms devoid of snags. Two tractors pull a tanks containing flowing, aerated water. When needed
seine through the pond; one tractor pulls a hydraulically‐ in the processing plant, fish are removed from the
operated seine reel that serves as a seine storage unit. tank, weighed and stunned with alternating current
Once the two tractors have moved the length of the electricity. Stunning renders the fish immobile and
makes them easier to handle in the processing line.
430 Aquaculture
Figure 19.11 Channel catfish are scooped
from the live car and loaded onto live‐haul
trucks for transport to the processing
plant. Source: Reproduced with permission
from Les Torrans, 2017.
Much processing is done by hand, but there is a trend uted to a significant reduction in US catfish production.
towards increased automation to reduce processing Beginning in the late 1990s, market growth slowed due
costs. A variety of products are marketed, with com- to competition from imported pangasiid catfishes from
mon products being fillets, fillet strips, nuggets (the Vietnam, imported channel catfish from China, and
‘belly flap’ section removed from the fillet), steaks and general competition within the seafood marketplace;
whole dressed fish. Frozen fillets account for the larg- especially from farm‐raised tilapia. More recently,
est portion (~55%) of total sales. Overall, about half of increased energy costs and higher grain prices com-
a live catfish is converted into saleable products after bined to cause dramatic increases in feed costs.
processing. Interactions among increased feed costs, increased
operating expenses due to high energy costs, and com-
Compared to channel catfish, hybrids have 2–3% petition from imports will certainly have long‐term
higher whole dressed fish yield (% of product relative to impacts on US catfish farming, although the nature of
whole fish weight), 1–2% higher shank fillet yield and those impacts is impossible to predict.
1–1.5% higher nugget yield (Bosworth et al., 2004). The
higher meat yield of hybrids is beneficial to processors Annual yields of catfish average ca. 4000 kg/ha under
and is another reason for the increase in hybrid catfish commercial conditions, which is less than 25% of that
production. Hybrids are similar enough in body shape attainable under controlled, experimental conditions.
and skeletal structure to channel catfish to be processed Losses to infectious diseases and bird depredation,
on machines set for channel catfish. Currently most pro- postponement of harvests by frequent episodes of off‐
cessors run a mix of channel and hybrid catfish and do flavour, and inefficient aeration in large commercial
not change machine settings based on the type of fish ponds account for the difference between potential and
being processed, although, as more hybrids are grown in actual farm productivity. Clearly, technological improve-
the future, machine settings specific to hybrids will likely ments in management of those problems will improve
become widespread. farm economic performance. Advances in aeration prac-
tices offer considerable potential for improving farm
19.3.6 The Future of Channel and Hybrid economic performance. For example, annual production
Catfish Farming of 15 000–20 000 kg/ha can be achieved under commer-
Channel catfish aquaculture expanded at a 10–20% cial conditions by growing hybrid catfish in split ponds
annual rate in the period from 1980 to 2000. Industry and intensively aerated ponds. Even better yields and
growth was facilitated by a stable US economy, low more efficient production may soon be realised as
feed prices, aggressive marketing, and a general trend improved germplasm becomes widely available and
towards more fish in the diet of American consumers. production systems are improved. In addition, improve-
Since 2003, negative economic forces and lack of ments in feeding practices can dramatically impact
growth in per‐capita fish consumption have contrib- profitability because feed represents the largest single
cost of production.
19.4 Clariid Catfishes Catfishes 431
The family Clariidae (air‐breathing catfishes) consists of Figure 19.12 North African catfish on postage stamps from
14 genera native to Africa, the Indian subcontinent, and Zimbabwe and Namibia. Source: Reproduced with permission
south‐eastern Asia. Of about 60 species currently rec- from Dr Heok Hee Ng, 2017.
ognised, about half are native to Africa and half to
the Indian subcontinent and south‐eastern Asia. that in certain pangasiids, which use the swim bladder as
Introductions have been made elsewhere, often with an accessory respiratory organ. The highly efficient
negative consequences for native fish communities. suprabranchial organ largely explains the survival and
Breeding populations of Clarias gariepinus are wide- distribution of clariids in tropical regions subject to
spread in Brazil after introduction for aquaculture and annual dry seasons and prolonged droughts that periodi-
C. batrachus populations have become established in cally reduce many water bodies to no more than a muddy
Florida and other states in the USA after escapes from depression. The ability to air‐breathe and tolerate
ornamental fish farms and home aquaria. extremely low dissolved oxygen concentrations is also
beneficial under intensive aquaculture conditions.
Many clariid catfishes are regionally important food
resources and several species have considerable aquacul- In addition to notable tolerance of limited oxygen
ture potential. The North African catfish (also called the supplies, North African catfish have wide tolerance to
sharptooth catfish) (Clarias gariepinus) is the most other environmental conditions. Optimum salinity range
common aquaculture species, at least in Africa, but is from near 0‰ to about 3‰, and they tolerate salinities
C. batrachus and C. macrocephalus are of economic up to about 12‰. Optimum temperatures for growth are
importance in Asia. Two species of another clariid genus, 28–30 °C and thermal limits for adults are from about
Heterobranchus longifilis and H. bidorsalis, have been 8–10 °C to 35–40 °C. They tolerate extremes in turbidity
used to produce hybrids with the North African catfish. and pH.
The hybrids are often identified as ‘Heteroclarias’ and
may have potential for African aquaculture. North African catfish mature within 1 year and spawn
once annually in flooded deltas and littoral areas during
Global aquaculture production of Clarias spp. is esti- the onset of the rainy season. Eggs adhere to vegetation
mated at about 1.1 × 106 t, which is ~90% of the total and other substrates until they hatch in 1–2 days. Adults
worldwide clariid catfish production. About 75% of return to the river or lake and juveniles remain in the
world Clarias spp. aquaculture production is from Asia,
but the fish are of comparatively minor overall signifi-
cance in that region because many superior aquaculture
species are available, such as the major and minor carps,
common carp, pangasiids and tilapias. Although overall
Clarias spp. aquaculture production in Africa is much
smaller than in Asia, there is only one other aquaculture
species that is well‐suited to African conditions: Nile
tilapia, Oreochromis niloticus. In many African countries
the North African catfish is the preferred species for
aquaculture and this section will focus predominantly on
culture of that species in Africa.
19.4.1 Biology
Clariid catfishes have an elongated body, large, depressed
bony head, long dorsal and anal fins, and four pairs of
barbels (Figure 19.12). They possess pectoral fin spines
but lack a dorsal fin spine and an adipose fin. The unique
synapomorphic (shared) trait of the Clariidae is the
suprabranchial organ formed by modified extensions of
the second and fourth gill arches. The suprabranchial
organ is a highly vascularised, accessory respiratory
organ that can absorb oxygen directly from the atmos-
phere, allowing fish to survive out of water for long periods.
This air‐breathing adaptation is distinctly different from
432 Aquaculture
inundated area without parental care. This provides
juveniles with vast areas of recently flooded land to
forage and grow. Juveniles return to the lake or river
when they are 1.5–2.5 cm long. Fry and juveniles feed
mainly on zooplankton but turn to a more omnivorous
and even piscivorous diet as they grow. North African
catfish may grow to more than 1.5 m in length and weigh
more than 50 kg.
19.4.2 Aquaculture Figure 19.13 African farmer with ~1‐kg North African catfish
raised in subsistence. Source: Reproduced with permission from
North African catfish have many advantages for aqua- Les Torrans, 2017.
culture in Africa. They are native across much of the
continent and their reduced intramuscular bones (there However, that technology exceeded the capability of
are fewer fine bones in their meat compared to tilapias most rural aquaculture programs in Africa until recently
and carps) make them a preferred food fish in regions when reliable techniques were developed for large‐scale
that do not have cultural or religious objections against reproduction and culture under practical farming condi-
fish lacking scales. They often bring a higher market‐ tions. Pioneering research by Dutch scientists provided
place price than other fish because they can be sold live. appropriate technology and that technology was effec-
tively transferred by government and non‐government
They have numerous long gill rakers on the first gill aid organisations and numerous national fisheries
arch allowing them to use zooplankton as a food, even departments. Availability of fingerlings is now rarely a
into adult stages. These features, coupled with fast limiting constraint to intensive commercial aquaculture.
growth, omnivorous feeding habit (eliminating the need
for highly specialised diets), and generally good resist- African farmers have learned to maintain brood fish and
ance to poor water quality and diseases, make North inject females with spawning hormones such as LHRHa,
African catfish a good choice for African aquaculture. carp pituitary extract or fresh Clarias pituitary extract
removed from male brood fish. Eggs are then stripped
North African catfish have long been used in polycul- from ovulating females and mixed with a sperm solution
ture with mixed‐sex tilapia as predator or ‘police fish’ to prepared from fresh male testes. Eggs may be incubated
control unwanted tilapia reproduction. Lack of finger- and hatched in McDonald hatching jars or scattered on
lings constrained development of North African catfish fibrous material and allowed to adhere and hatch unat-
aquaculture on its own merits until about 2000. Prior to tended in concrete tanks or small outdoor ponds. North
that, North African catfish farming was largely limited to
growth of incidental wild fish that entered the ponds
from adjoining water bodies or stocking small numbers
of fingerlings bought from commercial fishermen.
In addition to relatively low‐intensity polyculture with
tilapia often seen in subsistence aquaculture (Figure 19.13),
North African catfish are now farmed commercially in
monoculture in concrete tanks and lined and unlined
earthen ponds. The fish can be raised in cages in reservoirs
in both East and West Africa as are tilapia, but this produc-
tion system is rarely used for North African catfish.
19.4.2.1 Reproduction and Spawning
North African catfish can spawn naturally in earthen
aquaculture ponds, but this rarely results in significant
fingerling production. Timing of pond spawning with zoo-
plankton blooms necessary for good fry survival is diffi-
cult and the presence of predators (tilapia, amphibians
and insects) in most ponds results in low fry survival.
Controlled reproduction of North African catfish
involves hormone injections to induce ovulation and
hand‐stripping to obtain gametes, but it is no more com-
plicated than that for other commercially‐farmed fish.
African catfish have a high fecundity (60 000 to 70 000 Catfishes 433
eggs/kg of female). Fry can be stocked directly into ferti-
lised earthen ponds but preparation of ponds to obtain pounded and used in soups to flavour rice or starchy
abundant zooplankton is necessary for best fry survival. tubers. Fish are gutted but consumed skin‐on and head‐
This practice is poorly understood and often not attempted, on, leaving very little waste. With growth of commercial
and most successful fingerling producers feed swim‐up fry farming, fish are now marketed and prepared in a variety
in tanks using a high‐protein (48%) manufactured fry feed. of forms, including baked, fried and broiled (grilled);
whole fish, steaks, fillets, as well as the more traditional
While North African catfish normally spawn once hot smoking, which is now done in commercial‐scale
annually in nature, the spawning season in captivity can be smokehouses. Fillets are not traditionally marketed in
extended to several months by separating the sexes and Africa, although North African catfish do have a high fillet
using some younger‐aged females which may mature later yield. Fillets may become more popular in hotel and tour-
in the season. More sophisticated techniques, such as con- ist markets and for export. Most commercial p roduction
trolling temperature and photoperiod to shift the spawn- is now in or near major urban areas, where fish are sold
ing season, is likely to have little widespread application. live or ice‐packed (rarely frozen) for distribution.
19.4.2.2 Fingerling Production 19.4.3 The Future of Clarias Aquaculture
Most fingerlings are grown in small concrete tanks or Most North African catfish now produced are descendants
lined earthen ponds. After fry begin accepting feed, par- of genetically unimproved wild fish. With a rapidly
ticle size is gradually increased as fish grow. North African expanding commercial industry, genetic improvement
catfish fry and fingerlings are cannibalistic, so it is impor- programs are being pursued across Africa by both the
tant to incubate and hatch egg batches of uniform age and private and public sectors. Given the excellent growth
to grade fry and fingerlings to maintain uniform size. rates currently achieved with North African catfish, cost
and availability of quality feed and marketing issues are
19.4.2.3 Grow‐out priorities rather than breeding programs.
In many African countries, aquaculture has developed
beyond subsistence farming of small‐scale and low‐ The hybrid ♀ Heterobranchus longifilis × ♂ C. gariepinus
intensity into a viable commercial enterprise. In Nigeria, (‘Heteroclarias’) also shows promise as a food fish. Aside
more than 190 000 t of Clarias spp. were produced in from the need to maintain a second species of broodstock,
2014, primarily in small concrete tanks and ponds. production of hybrids is no more complicated than pro-
Fingerlings are typically stocked at high densities (40– duction of either parent since both processes require
100/m3) and fed an extruded feed several times daily. hormone injections and hand‐stripping. Growth of the
There are several mills in Africa manufacturing fish feed hybrid can be better than either parent, and dressout
from locally‐sourced ingredients, but most commercial percentage is often better as well due to delayed or
farms rely on feed imported from Europe or Brazil. limited maturation of the F1 females. However, since the
Higher‐protein feeds (35–45%) are often used but lower F1 hybrids are fertile, environmental concerns may limit
protein feeds (28–32%) are probably adequate if fish are the production of the hybrid.
fed to satiation. Due to their air‐breathing ability, they
can be reared at very high densities in concrete tanks in In areas of Africa where clariids are preferred over tila-
water essentially devoid of dissolved oxygen and with pia, production will undoubtedly increase. There is also
partial water exchange to remove waste products. Little a substantial market for Clarias fingerlings in the Lake
or no water exchange is used in outdoor ponds. Diseases Victoria basin for use as bait for the Nile perch (Lates
are generally not a problem. Production cycles vary from niloticus) sports fishery. North African catfish production
6–12 mo depending on initial fingerling size, stocking technology is well‐developed and commercialised in
density, feeding rates, and the desired market size. North both East and West Africa, and will steadily improve
African catfish of almost any size can be marketed but efficiency over time. The demand for fish in Africa is
most commercial producers aim for a minimum market great and growing and there is little reason that African
size of 200–500 g, which can be reached in 6 months. aquaculture cannot meet more of that demand.
19.4.2.4 Marketing 19.5 Summary
Prior to large‐scale commercial aquaculture, marketing
Clarias spp. was rarely an issue. Harvests from subsistence ●● Catfishes (order Siluriformes) are the third most com-
ponds were sold to neighbours on the pond bank, monly farmed fish in the world, behind only carps and
consumed in a day or two by the family, or hot‐smoked tilapias. In 2014, more than 4.5 million t of catfish were
over a kitchen fire for longer‐term storage until they were grown in aquaculture, nearly all in freshwater.
434 Aquaculture China. Major challenges to ictalurid aquaculture in the
USA are competition from less‐expensive imported
●● Pangasiid catfishes are farmed primarily in tropical pangasiid catfish and rising production costs. Advances
south‐eastern Asia. More than 2.1 million t of pan- in farming technologies, including increasing use of
gasiid catfish were grown there in aquaculture in 2014. hybrid catfish grown in intensively managed ponds,
Vietnam accounts for slightly more than 50% of total will improve economic performance.
pangasiid production, which is mainly for export. The ●● Clariid catfishes are native to Africa, the Indian sub-
major species grown in Vietnam is tra, or striped cat- continent and south‐eastern Asia, and are important
fish (Pangasianodon hypophthalmus), which is a hardy, food fish throughout the region. Global clariid pro-
facultative air‐breather that can be farmed at very high duction was ca. 1.1 million t in 2014 and various
densities in ponds and cages. Clarius species (especially Clarius gariepinus, the
North African catfish) comprised almost 90% of that
●● Major challenges in tra aquaculture are an increasing total. This fish is especially important as a farmed
incidence of infectious diseases and a reputation as species in Africa.
being only an inexpensive ‘whitefish’ alternative. ●● The North African catfish is often raised in small‐
Certification programs are being implemented to scale, low‐intensity ponds as part of subsistence
enhance the image of the fish and help establish new farming, but is increasingly being farmed in high‐
markets. intensity tanks and ponds. The fish is well‐suited to
intensive production because it is generally hardy
●● Ictalurid catfishes are native to North America. and is a facultative air‐breather. The future of
Global ictalurid production was ca. 390 000 t in Clarius aquaculture in Africa is bright because
2014: about 60% were grown in China and 35% the adoption of new technologies (such as use of
United States, where it is the most important improved germplasm) and new market develop-
aquaculture species. The major species grown are ment can easily increase production efficiency and
the channel catfish (Ictalurus punctatus) and the demand.
hybrid ♀ channel catfish × ♂ blue catfish (Ictalurus
furcatus).
●● Most ictalurids are farmed in ponds in the USA,
although many are farmed in reservoir‐sited cages in
R eferences Nguyen, T. P. (2013). On‐farm feed management practices
for striped catfish (Pangasianodon hypophthalmus) in
Bosworth, B. G., Wolters, W. R., Silva, J. L. et al. (2004). Mekong River Delta, Viet Nam. In: Hasan, M.R. and
Comparison of production, meat yield, and meat quality New, M.B. (Eds.) On‐Farm Feeding and Feed
traits of NWAC 103 line channel catfish (Ictalurus Management in Aquaculture. Pp. 241–267. FAO
punctatus), Norris line channel catfish, and channel Fisheries and Aquaculture Technical Paper, 583. [http://
catfish female × blue catfish male (I. furcatus) F1 hybrids. www.fao.org/3/a–i3481e.pdf ] (viewed June 2016).
North American Journal of Aquaculture, 66(3), 177–183.
Phan, L. T., Bui, T. M., Nguyen, T. T. T. et al. (2009).
Bui, T. M., Phan, L. T., Ingran, B. A. et al. (2010). Seed Current status of farming practices of striped catfish,
production practices of striped catfish, Pangasianodon Pangasianodon hypophthalmus in the Mekong Delta,
hypophthalmus, in the Mekong Delta region, Vietnam. Vietnam. Aquaculture, 296(3), 227–236.
Aquaculture, 306(1), 92–100.
Phu, T. M., Phuong, N. T., Dung, T. T. et al. (2015). An
Dung, T. T., Ngoc, N. T. N., Thinh, N. Q. et al. (2008). evaluation of fish health‐management practices and
Common diseases of Pangasius catfish farmed in Viet occupational health hazards associated with Pangasius
Nam. Global Aquaculture Advocate, 13(4), 77–78. catfish (Pangasianodon hypophthalmus) aquaculture in
the Mekong Delta, Vietnam. Aquaculture Research,
Glencross, B., Hien, T. T. T., Phuong, N. T. et al. (2011). [published online 15 March 2015, doi:101111/are.12728]
A factorial approach to defining the energy and protein
requirements of Tra catfish, Pangasianodon Rico, A., Satapornvanit, K., Haque, M. M. et al. (2012). Use
hypothalamus. Aquaculture Nutrition, 17, 396–405. of chemicals and biological products in Asian
aquaculture and their potential environmental risks: a
Li, M. H., Robinson, E. H. and Manning, B. B. (2004). critical review. Reviews in Aquaculture, 4(2), 75–93.
Nutrition. In: Tucker, C.S. and Hargreaves, J.A. (Eds.)
Biology and Culture of Channel Catfish. Pp. 279–323.
Elsevier, Amsterdam.
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and Feeding. In: Tucker, C.S. and Hargreaves, J.A. (Eds.)
Biology and Culture of Channel Catfish. Pp. 324–348. Tucker, C. S., Brune, D. E. and Torrans E. L. (2014).
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Tucker, C. S. (2000). Off‐flavor problems in aquaculture.
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vaccination of channel catfish against enteric septicemia
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and Culture of Channel Catfish. Elsevier, Amsterdam. ictaluri isolate. Journal of Aquatic Animal Health, 27,
135–143.
437
20
Marine Finfish Aquaculture
Wade O. Watanabe, Md Shah Alam, Patrick M. Carroll, Harry V. Daniels and Jeffrey M. Hinshaw
CHAPTER MENU
20.1 Introduction, 437 20.9 Gilthead Sea Bream, 456
20.2 Importance of Marine Fish Aquaculture, 437 20.10 Yellowtail Amberjack, 459
20.3 Hatcheries, 440 20.11 Red Sea Bream, 462
20.4 Grow‐Out Systems, 444 20.12 Cobia, 465
20.5 Nutrition and Feeds, 448 20.13 Flatfishes, 468
20.6 Marine Fishes in Aquaculture, 449 20.14 Sturgeon, 477
20.7 Milkfish, 449 20.15 Summary, 481
20.8 European Seabass, 454
References, 482
20.1 Introduction Culture practices are likewise diverse and impossible
to characterise generically. This chapter provides a
Marine finfish aquaculture includes a diverse array of general overview of practices used for the marine fish
more than 90 species from 34 families that inhabit aquaculture and then provides eight ‘case studies’ of
marine coastal or oceanic waters of the world for a sig- farmed marine fish. The case studies represent some of
nificant portion of their life cycles (Table 20.1).1 These the important food fish in terms of annual production
species occur in a wide variety of habitats and require the and also illustrate the diversity of practices used in
marine environment at distinctly different stages of their marine aquaculture. Salmonids and marine ornamental
life cycles. They range from stenohaline marine species fish are covered in separate chapters.
(e.g., yellowtail amberjack) that spend their entire lives in
marine waters, to euryhaline species (e.g., milkfish) that 20.2 Importance of Marine Fish
use estuaries and inland waters with very low salinities— Aquaculture
including fresh water—for a substantial portion of their
life cycles. They also include anadromous species (e.g., Aquaculture of freshwater fish has historically dominated
sturgeon) that spawn in fresh water but feed in brackish- world food fish production. Marine fish comprise a
water estuaries, or migrate along coastlines under fully significant, but smaller, percentage of total aquaculture
marine conditions, and they include catadromous spe- production. In 2014, total world finfish aquaculture was
cies (e.g., European eel) that begin their life cycle in the ~46 million t, valued at USD 82.4 billion. Freshwater fish
ocean, but spend the majority of their lives in inland production was ~43 million t, or 93% of total fish pro-
fresh water or coastal brackish water and then return to duction, valued at USD 70.9 billion, or 86.0% of the total
the ocean to spawn and then die. value. World aquaculture production of marine fish was
3.37 million t in 2014, which was 7% of total fish produc-
1 All production data in this chapter were obtained from the 2016 tion but was valued at USD 11.5 billion, or 14% of the
FAO Fishery and Aquaculture Statistics FishStatJ database http:// total value. Marine fish farming has disproportionately
www.fao.org/fishery/statistics/software/fishstatj/en
Aquaculture: Farming Aquatic Animals and Plants, Third Edition. Edited by John S. Lucas, Paul C. Southgate and Craig S. Tucker.
© 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd.
Table 20.1 Representative examples of marine finfish produced through aquaculture around the world, including global production (t) in 2014, source of seedstock, and growout
aquaculture systems used for their production.
Common name Global Family Species Source of seedstock Growout culture systems2
Aquaculture
Milkfish Production (t) Chanidae Chanos chanos Mainly hatchery, wild Ponds, pens, sea cages
European seabass (2014)1 Moronidae Dicentrarchus labrax Hatchery Ponds, lagoons, mainly sea
cages
Gilthead sea bream 1 039 184 Sparidae Sparus aurata Hatchery Ponds, lagoons, pens, tanks,
156 450 mainly sea cages
Orange‐spotted grouper Serranidae Epinephelus coioides Hatchery Open ocean cages
Japanese amberjack (yellowtail) 143 688 Carangidae Seriola quinqueradiata Mainly wild, hatchery Net pens, sea cages
Large yellow croaker Sciaenidae Larimichthys crocea Hatchery Sea cages
Japanese seabass (spotted seabass) 138 191 Lateolabracidae Lateolabrax japonicus Hatchery Sea cages
Snubnose pompano 135 998 Carangidae Trachinotus blochii Hatchery Ponds, tanks, sea cages
Sturgeons (not including Beluga)5 127 917 Acipenseridae Various spp.5 Hatchery Tanks, ponds, cages, RAS
Red drum 117 185 Sciaenidae Sciaenops ocellatus Hatchery, outdoor Tanks, sea cages
110 194 ponds, indoor tanks
Turbot Scopthalmidae Scophthalmus maximus Hatchery Sea cages, RAS
Silver sea bream 90 000 Sparidae Pagrus auratus Hatchery Sea cages
Barramundi (Australian or Asian 72 819 Centropomidae Lates calcarifer Hatchery Ponds, RAS, sea cages
seabass)
Red sea bream 71 851 Sparidae Pagrus major Mainly hatchery, wild Sea cages
Bastard halibut (olive flounder, 65 566 Paralichthydae Paralichthys olivaceous Hatchery Tanks
Japanese flounder) 63 722
Cobia Rachycentridae Rachycentron canadum Hatchery Open ocean cages
Korean rockfish 56 861a Sebastidae Sebastes schlegelii Hatchery Sea cages
Pacific bluefin tuna 44 733 Scombridae Thunnus orientalis Wild Open ocean cages
Tiger pufferfish Tetraodontidae Takifugu rubripes Hatchery Sea cages
Greater amberjack 40 329 Carangidae Seriola dumerili Mainly wild Sea cages
Meagre 24 598 Sciaenidae Argyrosomus regius Hatchery Tanks, sea cages
Mangrove red snapper 22 986 Lutjanidae Lutjanus argentimaculatus Wild, hatchery Sea cages
Righteye flounder3 22 825 Pleuronectidae Various spp. (not including Hatchery Tanks, RAS
20 509 Atlantic halibut)3
Flathead grey mullet 11 748 Mugilidae Mugil cephalus Mainly wild, hatchery Ponds
10 392
9 629
8 521
Southern bluefin tuna 7 544 Scombridae Thunnus maccoyii Wild Open ocean cages
Atlantic bluefin tuna 4 253 Scombridae Thunnus thynnus Wild Open ocean cages
Atlantic cod 1 696 Gadidae Gadus morhua Hatchery Sea cages
Atlantic halibut 1 327 Pleuronectidae Hippoglossus hippoglossus Hatchery Tanks, RAS
Lefteye flounders4 Bothidae Not specified Hatchery Flow through tanks
European eel 572 Anguillidae Anguilla anguilla Wild RAS
European sturgeon (Beluga) 94 Acipenseridae Huso huso Hatchery Raceways, tanks, RAS
Sixfinger threadfin 3 Polynemidae Polydactylus sexfilis Hatchery Open ocean cages
1
1 FAO FishStatJ (2016).
2 tanks = flow‐through tanks, RAS = recirculating aquaculture systems, sea cages = nearshore cages.
3 Pleuronectes platessa, Platichthys flesus, Limanda ferruginea, Pseudopleuronectes americanus, Microstomus kitt, Hippoglossoides platessoides, Hippoglossus stenolepsis.
4 Not specfied.
5 Acipenser baerii, A. gueldenstaedtii, A. ruthenus, A. naccarii, H. huso x A. ruthenus hybrid, and A. transmontanus.
a MAFF (2016). Data is for 2013.
440 Aquaculture
higher value because it includes many species with
higher market value (and higher production costs) than
most freshwater‐farmed fish. The importance of marine
fish farming will undoubtedly increase as world popula-
tion growth and rising incomes in developing countries
drive the demand for high‐quality fish.
20.3 Hatcheries Figure 20.1 Sole Solea solea larva at 7 days post‐hatching. Source:
© Hans Hillewaert via Wikimedia Commons.
There are fundamental biotechnical reasons for the
lag in development of marine fish aquaculture com- limited yolk reserves. The eggs hatch into tiny (3–5 mm
pared to freshwater species. Production of seedstock in total length), free‐living larvae (Figure 20.1) that
is a continuing bottleneck for many marine fish spe- receive no parental care, develop rapidly, are very sus-
cies, and a major challenge in marine finfish hatchery ceptible to environmental stressors and experience
technology is related to the complex life cycles of high mortality in nature. Their meagre yolk reserves
marine fish compared to freshwater fish. Closing the provide limited sustenance for the larvae, which are
life cycle was relatively straightforward for the trouts, weak swimmers and have primitive digestive systems at
catfishes, carps, and tilapias—which are easy to spawn the start of feeding when their yolk reserves are
in captivity. Many freshwater fish also produce large depleted. Since larval yolk reserves originate from the
larvae with large yolk sacs (Figure 19.7) that provides parental broodfish, the nutritional requirements of the
newly‐hatched fish with sufficient food reserves to early larvae may be profoundly influenced by brood-
sustain significant development toward the juvenile stock nutrition, but experimental data on specific nutri-
stage. Once their yolk is consumed and exogenous ent requirements in broodstock diets is limited for
feeding begins, many freshwater ‘fry’ are hardy, have a most marine finfish species.
large mouth and a well‐developed digestive system
and are able to thrive on commercially available feeds First‐feeding larvae of marine fish differ in appearance
that are formulated specifically to meet their nutri- from the adult form, and they undergo a relatively long
tional needs. period of development before the adult form is attained,
typically around 30–50 days post‐hatching (dph). In flat-
In contrast, the life cycles of many marine fish are not fish, the transition from larvae to juvenile involves a dra-
well understood. Most species spawn in oceanic waters matic metamorphic transformation from a pelagic to a
at locations that are not precisely known, and they pro- benthic mode of existence. During metamorphosis, there
duce tiny, transparent, microscopic eggs and larvae that are drastic changes in body symmetry, organisation of
are part of the zooplankton, and their diurnal vertical the internal organs, and fish behaviour that pose unique
migrations as well as their dispersal patterns are difficult challenges for the larval culturist.
to observe and track. Knowledge of life histories, includ-
ing spawning requirements and larval diets, behaviour First‐feeding marine fish larvae must be provided
and migratory patterns is incomplete. Many marine fish with food as soon as the mouth is open since the yolk is
do not breed freely in captivity, but the precise environ- exhausted by this time, and any delay in feeding will
mental cues to obtain natural spawning under hatchery reduce survival. A small larva has an even smaller
conditions are difficult to determine experimentally. Fish mouth gape, which further limits the size of food parti-
culturists circumvent their lack of knowledge of repro- cles that they can ingest. Since small larval fish are una-
ductive control by inducing fish to spawn with hormones ble to c onsume or digest ‘artificial’ diets (section 9.7),
(section 6.2.1; Figure 6.1). However, protocols for condi- living planktonic prey organisms must be fed to the lar-
tioning captive broodstock to attain sexual maturity and vae as their initial foodstuffs. Therefore, live planktonic
reliable hormonal therapies for inducing spawning and
producing fertilised eggs of high quality require in‐depth
knowledge of fish reproductive endocrinology and
broodstock nutrition. This has required significant long‐
term investments in research by both university and pri-
vate‐sector researchers.
Most marine fish with aquaculture potential produce
large numbers of very small eggs (0.8–1.0 mm) with
foods are essential for rearing marine finfish larvae at Marine Finfish Aquaculture 441
present.
food chain, a large percentage of hatchery space is
Prey organisms must be abundant, slow swimming, d edicated to microalgae production.
and small enough for larvae to capture easily. But they
must not be so abundant that they overwhelm the fish A typical microalga used in hatcheries is Nanno
larvae or produce excessive wastes that become toxic to chloropsis oculata because of its tolerance to a wide
the fish larvae. Cultured planktonic prey grown in hatch- range of temperatures and salinities. It has a favorable
eries have limited nutritional value and therefore must be fatty acid profile that is reflected in the fatty acid content
enriched with nutrients such as essential fatty acids. The of rotifers that feed on the microalgae and, therefore, in
challenge of raising marine finfish larvae is, therefore, to the nutritional value of the rotifers to marine fish larvae.
provide a continuous supply of live planktonic food
organisms of the correct sizes and nutritional value, with- The basic strategy for culturing N. oculata is to pro-
out contaminating the environment. These requirements gressively scale up from a stock test‐tube culture to
also require special design considerations for larval rear- indoor flask cultures, then to carboy and cylinder cul-
ing systems that allow waste products to be flushed from tures, and finally to outdoor cultures in tanks, raceways
the culture system, while retaining the small living plank- or ponds until harvestable volumes are reached
tonic prey and the fish larvae in the rearing tank without (Figure 9.3). Aseptic techniques are used to prevent cul-
injury. Improving live food production techniques and ture from contamination from algae‐eating organisms
feeding strategies that are cost‐effective at industrial such as ciliates and rotifers. Continuous algal culture sys-
scales are a challenge for culturists. tems using enclosed photobioreactors made of transpar-
ent tubes or containers have enabled production of
20.3.1 Live Food Organisms and Artificial higher concentrations of microalgae in less space.
Feeds Another innovation that has eliminated the labour and
Since about 1975, culturists have selected a small num- hatchery space is the development of highly concen-
ber of food sources for feeding marine fish larvae. These trated algae available from commercial suppliers that can
live prey must be simple and cost‐effective to raise and be stored frozen for 2–3 yr.
versatile enough to use over a range of species, but also
palatable, digestible, and meet the energetic and nutrient Many commercial hatchery operations introduce
requirements of the larvae. Three groups of live prey are microalgae to the larval rearing tanks even before rotifers
commonly used for commercial‐scale culture of marine are fed. They may be directly consumed by some fish
fish larvae: larvae to stimulate feeding, provide micronutrients,
●● various species of microalgae (approximate size 2–20 µm); stimulate synthesis of digestive enzymes, act as immuno-
●● the rotifer Brachionus spp. (100–360 µm lorica length); logical stimulants to the larvae, supply exogenous
enzymes which the larvae need to digest zooplankton, or
and promote growth of beneficial bacteria in the larval diges-
●● brine shrimp Artemia spp. nauplii (420–800 µm). tive tract or in the rearing tank. Microalgae also maintain
Most dietary feeding regimes for marine fish larvae are the dietary value of the zooplankton that feed on micro-
based on these three basic feed types. In addition, oyster algae in the fish tanks. They improve water quality by
larvae (~40–60 µm) are sometimes fed to exceptionally assimilating nitrogenous wastes such as ammonia and
small larvae to help them grow until they can more easily have light‐shading effects to minimise the stress of artifi-
feed on rotifers. Cultured copepods are also being used cial lights on feeding. They can improve visibility of live
increasingly to supplement rotifers and Artemia. Finally, prey to fish larvae and result in more even distribution of
various artificial diets are used to substitute for live prey. larvae and prey to minimise crowding. Using microalgae
Additional details are provided in Chapter 9. as a background (‘greenwater’) is a common practice for
rearing the early larval stages of most marine fish species
20.3.1.1 Microalgae that use rotifers as a first feed.
Live feed production is the foundation of larval rearing.
Feeding larvae in a hatchery involves creating a food 20.3.1.2 Rotifers
chain in which the primary producer (microalgae) is Rotifers Brachionus spp. are microscopic filter‐feeding
used to feed a primary consumer (rotifers) which are in animals that are crucial as a first feed or ‘starter diet’ for
turn used to feed a secondary consumer, the larval fish. a variety of larval marine fish (Figure 9.6; section 9.4).
Because phytoplankton are needed as the base of the Rotifers are widely used since they swim slowly and are
easily captured by fish larvae, are tolerant of high densi-
ties and have short generation times that make them
suitable for mass culture.
Two species of rotifers are commonly used: a large (L‐type)
B. plicatilis (200–360 µm lorica length) and a small (S‐type)
442 Aquaculture Because of their larger size compared to rotifers, Artemia
nauplii are used to feed larger, more developed larvae.
B. rotundiformis (100–200 µm lorica length). The S‐type Artemia cysts are purchased commercially and are easily
is frequently used in marine fish culture because they are hatched by immersion in seawater for around 24 hr.
more easily eaten by small fish larvae with a small mouth
gape. Optimum growth temperatures are 28–35 °C for The newly hatched Instar I must be separated from
the S‐type and 18–25 °C for the L‐type. Rotifers repro- the empty cysts, which are indigestible to the fish larvae
duce asexually and sexually depending on their environ- and can block their digestive tracts. Various techniques
ment. Asexual reproduction has a shorter generation to separate cysts from nauplii, including using light to
time of 18–24 hr. Sudden changes in environment (e.g., attract the phototactic nauplii, decapsulation of cysts
salinity, temperature, food) can induce the rotifer to by chemical treatment before hatching, and by using
reproduce sexually which involves the production of cysts coated with iron which can be separated from the
resting eggs (cysts) that do not immediately hatch and Instar I nauplii after hatching by passing the nauplii
therefore involve longer generation times. The culturist through a pipe harvester containing a magnet which
therefore strives to maintain rotifers under optimum retains the cysts.
environmental conditions since asexual reproduction
produces the fastest growth rates. The first larval stage measures 400–500 µm. The Instar
I nauplius does not take up food as its digestive system is
The nutritional quality of the rotifer to the fish larvae not functional. Instar I nauplii quickly lose caloric con-
is influenced by their diet, which can be manipulated to tent and must be fed to fish as soon as possible after
meet the requirements of the fish larvae. The microalga hatching, otherwise their lower organic dry weight will
Nannochloropsis oculata is often used for rotifer culture reduce the amount of energy uptake by the larva per unit
in marine fish hatcheries because it has high levels of the hunting effort resulting in slower larval fish growth.
essential fatty acids eicosapentaenoic acid (EPA), doco-
sahexaenoic acid (DHA) and arachidonic acid (ARA). After 8–12 hr, the Instar I larvae molt to a second lar-
Rotifers may be enriched by incubating them in a variety val stage (Instar II metanauplii), which has a functional
of commercially available emulsions to boost their essen- digestive tract and is able to filter small food particles.
tial fatty acids and other nutrients. In general, enriched Fish larvae readily consume Instar II metanauplii,
diets increase growth and stress resistance in fish larvae which are enriched with commercial preparations to
and decrease pigmentation abnormalities. supplement essential nutrients such as fatty acids.
Enrichment procedures use various mixtures of selected
Many types of systems are used for rotifer culture, but microalgae, algae‐replacement products such as micro-
the batch culture system is most common. A culture tank encapsulated products, yeast, emulsified preparations
is filled with phytoplankton and inoculated with rotifers. of beneficial marine oils, or spray‐dried cells of hetero-
Additional phytoplankton is added on day 2 and the trophicallygrown algae such as Schizochytrium spp.
rotifers multiply and are harvestable by day 3. A small (see section 9.4.8).
portion is saved as an inoculant to repeat this cycle.
Several tanks are maintained and harvested at staggered The major problems associated with Artemia are costs,
timed intervals to ensure a continuous supply. To mini- care required for maximising their hatching and collec-
mise costs of raising microalgae as feed, artificial rotifer tion, and their limited nutritional value to many marine
diets have been developed that replace microalgae while finfish larvae. Live feeds such as Brachionus and Artemia
providing a nutritious rotifer. These artificial rotifer diets may also be bioencapsulated with a drug or vaccine and
may provide more predictable rotifer outputs and levels delivered orally to the larvae as prophylactic and thera-
of enrichment with essential fatty acids than can be peutic measures. For example, seabass fry can be vacci-
achieved by using microalgae. Use of artificial rotifer nated against the pathogenic Vibrio bacteria by feeding
diets in replacement of microalgae may significantly them Artemia incorporating the vaccine.
reduce the production costs of rotifers. High‐density
continuous rotifer culture systems are also being devel- 20.3.1.4 Copepods
oped to provide daily harvests from one tank to improve Copepods used in aquaculture are non‐parasitic forms of
culture stability and stabilise bacterial populations in the the orders Calanoida (planktonic), Harpacticoida (benthic)
culture while reducing space and labour requirements and Cyclopoida (both planktonic and benthic). Copepods
for the hatchery. used in marine finfish larviculture vary in size (25–800 µm)
depending on species and ontogenetic stage (nauplii,
20.3.1.3 Artemia copepodites, and adults). These filter‐feeding organisms
Artemia develop through many stages and sizes, each of provide a number of advantages for marine fish larval
which can be used as a food during different phases of culture. Different sizes of copepods may be offered to the
larval rearing (Figures 9.7). The newly hatched nauplius fish larvae depending on their needs. Although the nutri-
stage (Instar I) is critical for larval rearing of marine fish. tional composition of copepods reflects their diet during
culture, they are generally of higher nutritional value to Marine Finfish Aquaculture 443
marine fish larvae than Artemia. In addition, copepodites
and adults may contain higher levels of digestive enzymes, 20.3.2 Larval Culture Systems
which make them more digestible by the fish larvae. Their Two basic types of larval rearing systems are used:
erratic swimming movements also provide an attractive extensive and intensive. Extensive culture systems are
visual stimulus to feeding for the early fish larvae, which usually outdoors in ponds with volumes up to thousands
may rely mainly on sight for feeding. of cubic meters. Fertilised eggs or newly hatched larvae
are stocked at relatively low densities in a fertilised pond
Copepods reproduce sexually and are less suited inoculated with microalgae and zooplankton to provide
than rotifers for mass culture because they have a long a food source for the larvae. The microalgae and zoo-
life cycle of about a month, which makes it difficult to plankton are either cultured, or grown in another pond
create and maintain a culture of copepods that can and periodically pumped or collected in filter bag nets
reproduce quickly enough to sustain a large population and then transferred to the larval rearing pond. Larvae
of growing fish larvae. Rearing methods are similar to are grown for 1–2 months to produce early juveniles for
rotifers. They cannot be grown at densities as high as transfer to nurseries or for 2–6 months to produce
rotifers, and infrastructure and labour costs currently advanced juveniles for stocking into grow‐out systems.
limit production of sufficient quantities of live copep- Extensive larval rearing systems minimise operating
ods to replace rotifers and Artemia in commercial costs and can produce large numbers of juveniles more
marine food fish hatcheries. Despite their costs, the economically than intensive tanks, but management of
judicious use of copepods as a start feed or to supple- environmental conditions in the pond is difficult (or
ment rotifers and Artemia may be advantageous to impossible) and yields from such ponds are variable.
commercial hatcheries of some species that do not
readily consume rotifers as a first feed. The reader is Intensive larval culture uses indoor tanks usually less
referred to section 9.4.9.1 for more information on than 20 m3 (but up to 200 m3) stocked at a high density.
copepod culture. The tank shape is usually cylindrical to facilitate water
circulation and waste removal. Rotifers and Artemia
20.3.1.5 Artificial Microdiets are primarily fed to the fish larvae in intensive systems.
In addition to live prey organisms, larval culturists are These systems enable close observation and control of
attempting to use artificial microdiets to replace or sub- environmental conditions and feeding, including the
stitute for live feeds. A reduction in live‐food require- use of automated systems for feeding and cleaning
ments would reduce production costs. Artificial tanks and maintaining stable environmental conditions
microdiets must be of the proper particle size, physical (Figure 20.2).
performance (buoyancy, leaching), attractive, digestible
and must also have the proper balance of nutrients, while Lighting intensity and photoperiod are controlled to
remaining cost‐effective (Table 9.8). Complete replace- provide conditions that optimise feeding, which vary
ment microdiets for marine fish larviculture remain an
elusive goal (section 9.7); however, progress has been Figure 20.2 Marine fish larval rearing tank (2100 L) at the
made to improve the characteristics of these diets so that University of North Carolina Wilmington, USA. The tank has a
they can be fed at earlier stages (early weaning diet) or to skimmer to remove surface films, airstones, an automatic feeder
partially replace live food (co‐feeding diet). A common and standpipe screening to prevent loss of small fish. Source:
strategy is to co‐feed artificial microdiets with live feeds Reproduced with permission from Wade O. Watanabe, 2017.
and to gradually withdraw live feeds as microdiets are
increased. Complete weaning to artificial feeds is a grad-
ual process that may take up to several weeks depending
on fish species.
Cannibalism is often observed as larvae develop
from pre‐metamorphic through juvenile stages, and
providing ample feeds for the larvae is important to
reduce losses from intra‐fish aggression. This must be
balanced against overfeeding, since larval microdiets
may deteriorate quickly and reduce water quality. In
addition to optimising feeds and feeding regimes,
maintaining optimum fish densities and periodic grad-
ing of fish to minimise size variation are strategies used
to minimise cannibalism.
444 Aquaculture levels are also managed by strategic placement of
airstones and adjusting air flow to help larvae remain in
with species. Optimal light intensity may be related to the water column and feed on live prey. Optimal aeration
conditions that each species encounters in their natural levels encourage an even distribution of larvae and live
habitat and surface light intensities are highly variable prey in the water column. Inadequate aeration may cause
among species and practitioners. However, illumination larvae and live prey to aggregate, while excessive aeration
levels are affected by factors such as quality of light may cause larvae to be thrown against the tank walls, or
(spectra), tank colour, tank depth, and concentrations of create currents that hamper feeding by the larval fish.
microalgal cells (greenwater) that attenuate light. Since
marine finfish larvae are visual predators and need light Beneficial bacteria (probiotics) are sometimes used by
to hunt, longer photoperiods of 18 hr light: 6 hr dark are hatchery managers to manage the microbial environ-
often used in hatcheries to provide more time for the lar- ment for the benefit of the cultured fish larvae. Probiotics
vae to feed and grow. Continuous light or dark condi- compete with opportunistic pathogens in the rearing
tions, on the other hand, are generally avoided as they medium and in the gut microbiota to prevent bacterial
can impair feeding and normal development. diseases. Probiotics may inhibit pathogenic bacteria,
serve as a source of nutrients and enzymes to aid larval
Larvae may be fed by hand several times per day or feed digestion, and possibly enhance immunity against patho-
may be delivered using timer‐controlled peristaltic pumps genic bacteria.
connected to feed coolers. Coolers are filled in the morn-
ing with freshly‐enriched live prey and immediately refrig- Intensive larval culture systems are appropriate for
erated or chilled with ice (i.e., ‘cold‐banked’) to reduce species with well‐established culture requirements (e.g.,
metabolism of the prey organisms to maintain their nutri- European seabass, gilthead seabream, turbot). Water‐
tional value to the fish larvae throughout the day, long recirculating systems are increasingly used for hatchery
after the prey‐enrichment process is completed. Artificial production of marine fish because they allow greater
feeds are also fed by hand or with automatic feeders. control of environmental conditions. Semi‐extensive
(also known as mesocosm) systems use outdoor or
Within a few days of first‐feeding, an oily film accumu- indoor tanks (30–100 m3) or bags stocked at intermedi-
lates on the water surface of intensively‐managed larval ate larval densities and are managed using a combination
rearing tanks, consisting of rotifer shells, proteinaceous of extensive and intensive system techniques.
wastes, and oily material from prey‐enrichment media.
The surface film fosters bacterial growth and impedes 20.4 Grow‐Out Systems
the larvae from gulping air at the water surface to inflate
its swim bladder, an internal organ that helps the fish A major challenge to marine fish aquaculturists world-
control its buoyancy and to minimise energy in swim- wide is the development of cost‐effective and environ-
ming. Larvae that are unable to fill their swim bladders mentally sound grow‐out technologies for raising
expend more energy to stay in the water column, and this fingerlings to marketable sizes. Systems and methods for
leads to spinal deformities (lordosis), abnormal swim- grow‐out are remarkably diverse among species and can
ming and feeding, and reduced growth. In many marine vary from farm to farm for a given species. Systems
fish hatcheries, ‘surface skimming’ is practiced daily to include shallow coastal ponds, coastal pens, offshore
remove the oily film and to promote oxygen exchange cages, and land‐based flow‐through and intensive recir-
between the air‐water interface and dissolved oxygen culating aquaculture systems.
levels in the larval rearing tank. Surface skimmers are
floating traps, typically made from plastic pipe or hose in Preferred systems depend on many factors, including
square, triangle, or circular form, with an orifice on one geographical location, availability of brackish or seawa-
side through which air is blown tangentially to the water ter of required salinity, daily or seasonal variations in
surface, driving surface film and debris from the fish salinity and temperature, the environmental tolerance of
tank surface into the trap. Waste material accumulating the fish species to be cultured (e.g., fluctuations in salin-
inside the trap is removed at least once daily with a ity, temperature, and dissolved oxygen), and its ability to
beaker. tolerate crowding. Minimum space requirements are
also a major consideration for relatively large and fast‐
Larval rearing tanks also accumulate debris on the bot- swimming pelagic species (e.g., cobia, amberjack, and
tom, including dead planktonic prey, artificial feed, tuna). Marine fish aquaculture facilities—as with all ani-
microalgae, and bacteria. These solids must be removed mal production facilities—produce a variety of wastes
periodically to maintain water quality. that are potentially harmful to the environment. Grow‐
out systems use different approaches to maintaining
To maintain good water quality in the larval rearing water quality and managing wastes. Marine pen and cage
tank, water exchange is increased during the larval rear-
ing period as fish grow and feed inputs increase, but
water flow must be balanced against flushing the tiny
fish larvae and their live prey from the tank. Aeration
systems in particular face unique ecological, environ- Marine Finfish Aquaculture 445
mental, engineering, and aesthetic challenges to manag-
ing wastes that are currently being addressed to ensure 20.4.3 Recirculating Aquaculture Systems
sustainable growth of the industry. (RAS)
20.4.1 Coastal Ponds With the dramatic increase in coastal development and
multi‐user conflicts in environmentally sensitive coastal
Brackishwater ponds, either natural or man‐made, are zones, suitable sites for coastal aquaculture are at a pre-
the most popular type of aquaculture system for marine mium. Land‐based RAS are currently being used to raise
fish. The traditional grow‐out pond used for centuries is certain freshwater fish but are increasingly being evalu-
the shallow pond built with earthen dikes in coastal areas ated by researchers and farmers for production of marine
where the operator is able to take advantage of tidal fish (Figure 20.3). These systems are described in
exchange of water, which obviates the need for mechani- Chapters 3 and 4. In addition to advantages such as
cal pumping or aeration. In extensive pond systems, fer- reduced water use and reduced effluent‐discharge vol-
tilisers are applied to stimulate growth of natural ume, the concentrated wastes also provide aquacultur-
planktonic and benthic feeds for the fish, which must be ists with the opportunity to integrate marine finfish RAS
grown at low densities and with limited annual yields. In with other types of valuable mariculture products such
semi‐intensive pond systems, fish densities are increased, as marine worms (polychaetes), salt‐tolerant plants (e.g.,
but artificial feeds are used to supplement natural feeds. Salicornia), microalgae and molluscs (e.g., oysters) which
In intensive pond systems, fish are stocked at much filter waste nutrients from the RAS effluent before
higher densities and production relies entirely on artifi- discharge.
cial feeds. Energy inputs such as mechanical pumping of
water and aeration are usually required to maintain The saltwater culture medium poses unique technical
water quality conditions. challenges in maintaining equipment and proper water
quality when RAS are used for marine fish production.
Marine fish grown in outdoor ponds must be able to Saltwater accelerates corrosion of certain materials and
tolerate the daily and seasonal changes in temperatures specialised pumps and equipment designed for seawater
and salinities. Pond aquaculture of marine fish is more use are required. Seawater RAS systems generally need a
difficult at higher latitudes where wide seasonal varia- longer start‐up time for biological filters to efficiently
tions in temperature limit the growing season and the convert ammonia to nitrate (nitrification). Nitrifying
species that tolerate such conditions. In the tropics, bacteria acclimate to salinities ranging from freshwater
however, where favorable growth conditions extend to full strength seawater given sufficient time, but abrupt
year‐round, aquaculturists are able to exploit species changes in salinity greater than 5‰ may shock nitrifying
that tolerate the wide range of salinities that characterise bacteria and reduce rate of nitrification and require a lag
coastal brackish water ponds. The euryhaline and time to adapt to such salinity changes.
omnivorous milkfish is the best example of a fish well‐
suited for pond aquaculture. Recirculating systems cannot operate without some
exchange with new water to flush nitrate accumulating
20.4.2 Flow‐Through Systems from the nitrification process and to stabilise alkalinity
and pH. A typical exchange rate is about 10% of the sys-
Flow‐through systems are generally land‐based tanks tem volume per day (90% recirculation of water) when
constructed of various materials (plastic, fibreglass, con- fish biomass is high. As such, for every 100 000 litres
crete) using seawater pumped from the ocean and passed within the RAS, 10 000 litres of effluent laden with waste
through tanks holding the fish. Effluent is then dis- are released from the system. Freshwater RAS effluents
charged back to the ocean, either with or without treat- may be treated in municipal waste treatment facilities or
ment to remove wastes. Unlike recirculating systems applied onto agricultural lands as fertiliser or compost,
described below, there is little or no reuse of water after and the freshwater lost with these wastes may easily be
each pass through the culture system. The waste‐laden made up from terrestrial or municipal sources. Land
discharge can contribute to pollution of the receiving application is unacceptable with salt water which is toxic
waters, and the effluent discharged from flow‐through to terrestrial plants and animals, and artificial seawater
systems are increasingly treated to minimise environ- to make up significant daily water exchanges is cost‐pro-
mental pollution and reduce the spread of diseases hibitive. This requirement to maintain at least 10% water
among farms in close proximity. Flow‐through tank sys- exchange currently restricts marine RAS to coastal areas
tems are commonly used to grow marine fish such as where a continuous source of seawater is accessible.
rockfish in Korea and olive flounder in Korea and Japan.
High start‐up and operational costs have limited the
extent to which RAS systems have been used by com-
mercial marine fish farmers. Marine RAS technology
must be improved to increase the level of recirculation to
446 Aquaculture
Figure 20.3 Pilot‐scale recirculating aquaculture system for grow‐out of southern flounder in North Carolina, USA. Source: Reproduced
with permission from Wade O. Watanabe, 2017.
96–98% to reduce the amount of salt discharged with the northeastern USA. Approximately 99% of the water
effluent and to allow the marine fish aquaculture indus- is recirculated and fish wastes are used as fertiliser by
try to safely expand into almost any geographical loca- local farmers. University and private sector researchers
tion where seawater may be sourced or prepared. As the in the USA are also attempting to grow other species
percentage of water recirculation increases above 90%, (e.g., southern flounder and pompano) in low‐salinity
nitrate accumulates and depresses fish growth, increases RAS prepared by supplementing fresh groundwater with
stress, and results in increased incidence of disease. industrial salt to avoid the high costs of commercial arti-
Effluent discharge can also create adverse environmental ficial seawater mixes.
impacts. Alternative methods for removing nitrate from
RAS are needed, such as denitrification systems which 20.4.4 Coastal Pens and Cages
convert nitrate to nitrogen gas. Researchers are working Worldwide, many different species of fish are farmed
to develop improved denitrification and sludge‐diges- commercially in net pens and cages that are moored to
tion systems for near‐zero exchange RAS, but few com- the bottom in nearshore ocean waters such as estuaries
mercial companies claim to have the technology to grow and coastal embayments which provide natural protec-
marine fish in inland RAS with near‐zero‐exchange (i.e, tion from winds and waves (Figure 20.4). These systems
2% or less) of the total liquid effluent discharged from consist of a mesh enclosure to retain the fish while allow-
the RAS daily. ing water currents to maintain good water quality inside
the enclosure by carrying away waste products and
Marine fish aquaculturists currently grow marine fin- excess feed into the surrounding environment. If opera-
fish in inland‐based RAS by taking advantage of the nat- tions are not properly sited, wastes generated during
ural osmoregulatory ability of certain fish to thrive at grow‐out can increase nutrient concentrations in sur-
very low salinities. Australian seabass (barramundi), for rounding waters and contribute to harmful algal blooms,
example, are euryhaline and are being farmed at low
salinities in recirculating systems at an inland location in
Marine Finfish Aquaculture 447
Figure 20.4 Coastal sea cages used to grow gilthead sea bream and European seabass in the Argolic Gulf of the Aegean Sea, Greece.
Source: Photograph by Jean Housen (Own work) [CC BY‐SA 3.0 (http://creativecommons.org/licenses/by‐sa/3.0)], via Wikimedia Commons.
eutrophication and the spread of diseases among farms farming of selected marine fish in offshore areas at
in close proximity. Accumulation of wastes on the ocean considerable distances from the environmentally sensi-
floor can also eliminate native species and reduce ben- tive coastal zone. Open‐ocean aquaculture facilities
thic biodiversity. Nearshore aquaculture facilities may (Figure 20.5) generally consist of cages or net‐pens that
also compete with residential and recreational use of can be free‐floating, secured to a structure, moored to
nearshore coastal areas and are considered a form of the ocean bottom, or towed by a vessel. Self‐propelled
visual pollution by some. floating cages have also been designed to travel like ships
with favorable currents and be tracked by satellite. Open‐
To minimise environmental problems, fish farmers ocean facilities are exposed to wind and wave action and
have developed highly digestible feeds that generate less strong currents and severe weather conditions such as
wastes. Underwater cameras and automatic feeders are hurricanes that can limit access to cages for extended peri-
used to optimise consumption and minimise waste. In ods. Offshore systems are being engineered to withstand
some areas, a pen or cage site is ‘fallowed’ by removing these harsh offshore conditions and to be submerged in
all equipment and leaving the site undisturbed for a year the water column to avoid severe weather and conflicts
after harvest to allow the seafloor to recover from with navigational use of surface waters. Automated fish
impacts. monitoring and feeding systems and net cleaning robots
are being developed to reduce labour costs.
20.4.5 Offshore Cages and Net Pens
Due to limited space in nearshore coastal areas and the Development of offshore aquaculture is controversial.
potential for pollution and disease transfer, much of Proponents of open‐ocean aquaculture suggest that wastes
the growth in marine aquaculture is expected to be in the and excess feed will be assimilated efficiently in the open
ocean environment and will therefore have negligible
448 Aquaculture
Figure 20.5 Open ocean cage off the coast of Maine, USA. Source: Photograph by NOAA’s National Ocean Service (Aquaculture) [Public
domain], via Wikimedia Commons.
environmental impact compared to nearshore facilities. high‐energy, high‐protein feeds. These requirements are
However, impacts are difficult to assess because there is met by using relatively high inclusion levels of fishmeal
limited experience with the capacity of the marine envi- and fish oil obtained from small pelagic fish such as sar-
ronment to assimilate pollutants from offshore cage sys- dines, anchovies, herring, mackerel, and menhaden
tems. Preliminary studies of small‐scale operations have (see Chapters 5 and 8). The ‘reduction’ fisheries for these
shown negligible impacts on the marine environment, but feed‐fish are fully exploited, or have exceeded sustaina-
commercial‐scale operations must be evaluated. ble harvest levels globally, and are of ecological concern
because populations of small pelagic fish are important
Other potential environmental impacts of open‐ocean food for predators in marine ecosystems. Marine fish
aquaculture include the effects of antibiotics, parasiti- feeds use a disproportionate share of the fishmeal and
cides, and other drugs and anti‐biofoulant chemicals, fish oil consumed in aquaculture. For marine fish aqua-
transfer of diseases from cultured to wild fish, and culture to expand, fishmeal and fish oil in aquafeeds
entanglement of marine wildlife in fish cages and lines. need to be replaced with sustainable alternatives.
There is also concern about the escape of farmed fish or
their gametes and effects on the genetics of wild pop- Fish products are critical to broodstock conditioning
ulations. Concerns about genetic degradation of wild and egg and larval quality, but these life stages repre-
populations can potentially be addressed by limiting sent a small portion of protein and energy inputs to the
c ulture to native species of the local wild genotype and entire fish production process. For the grow‐out stage,
careful genetic management, including tagging of cul- which requires the majority of protein and energy
tured fish in the event of escape. From a business opera- inputs, it has been demonstrated that the requirements
tional standpoint, additional concerns include diver for protein, energy, fatty acids and micronutrients can
safety and health management, liability insurance, facility be met by using more sustainable alternative feedstuffs.
security and management, and logistical support. Scientific feed formulation and feeding practices have
resulted in substantial improvements in the efficiency
20.5 Nutrition and Feeds of feed use. Alternative feed ingredients include terres-
trial plant products (e.g., soybean meal, cottonseed
Nearly all fish that are farmed or candidates for commercial meal), animal‐processing byproducts (poultry, beef,
mariculture are carnivorous (milkfish being a notable swine, and fish) and fishery bycatch. Considerable vari-
exception). In culture, these fish generally require ation exists in the substitution limits of these various
materials for fishmeal and fish oil, depending on their
protein and energy content and digestibility and the Marine Finfish Aquaculture 449
species‐specific nutritional requirements.
of practices used to grow marine fish. Among families not
Much more progress has been made in identifying pro- included are the following: Serranidae (grouper), Sciaenidae
tein alternatives to fishmeal than for fish oil. In 1995, fish- (drum, croaker, meagre), Lateolabracidae (Japanese sea-
meal and fish oil inclusion in feeds for marine fish averaged bass), Centropomidae (Barramundi), Sebastidae (Korean
about 50% and 15%, respectively. In 2008, fishmeal and rockfish), Scombridae (tuna), Tetraodontidae (puffer-
fish oil inclusion declined to 29% and 8%, respectively and fish), Lutjanidae (snapper), Mugilidae (mullet), Gadidae
by 2020, it is expected that fishmeal and fish oil inclusion (cod), Anguillidae (eel), and Polynemidae (threadfin).
in aquafeeds for marine fish will decline to 12% and 4%, General information on marine fish aquaculture is available
respectively (Tacon et al., 2011). It is expected that total in Tucker (1998) and Moksness et al. (2004).
usage of fishmeal by the aquaculture sector will decrease
over the long term due in part to increased use of more 20.7 Milkfish
cost‐effective dietary fishmeal replacements. In contrast,
it is expected that use of fish oil by the aquaculture sector Milkfish (known as ‘bangus’ in the Philippines, ‘bandeng’
will continue to increase slowly due to the rising demand in Indonesia and ‘shi mu yu’ in Taiwan) is an esteemed
by the marine fish and crustaceans and the lack of cost‐ food fish and an important aquaculture species grown in
effective sources of dietary lipids to completely replace the brackishwater ponds in Southeast Asia. Milkfish farming
long‐chain highly unsaturated fatty acids in fish oil. is one of the oldest forms of marine aquaculture, with its
beginning in the fourteenth century in Indonesia and in
Fish oil is a natural source of the fatty acids EPA and DHA, the sixteenth century in Taiwan and the Philippines.
which are beneficial to human heart, cardiovascular, cogni-
tive, and neurological health. In nature, these fatty acids Global production has increased from 167 000 t in
originate from marine phytoplankton and are concentrated 1970 to more than 1 million t in 2014. The most impor-
up the food chain. Marine fish contain significantly higher tant producers in 2014 were the Philippines (390 000 t),
concentrations of long‐chain omega‐3 fatty acids than ter- Indonesia (578 000 t) and Taiwan (69 000 t). Almost all
restrial animals or freshwater fish, and it is economically milkfish found in the marketplace are grown on farms
advantageous to maintain high levels of these fatty acids in and very few are wild‐caught. Milkfish aquaculture is
farmed products. Substitution of terrestrial protein and ter- summarised by Lee (1995) and by Liao and Leano (2010).
restrial oil for fishmeal and fish oil in the diet of marine fish
reduces the levels of the long‐chain n‐3 fatty acids in their 20.7.1 Biology and Life History
body tissues, lowering health benefits and marketability. Milkfish is the only species in the family Chanidae (Order
Gonorynchiformes). It has an elongated body with a
It is possible to reduce the total amount of fishmeal silvery belly that blends to olive‐green or blue above
and fish oil used to grow some fish by using low dietary (Figure 20.6). Adults may reach 15–20 kg in nature.
inclusion levels for most of the grow‐out period and Milkfish are distributed throughout the tropical and
then feeding ‘finishing diets’ containing higher levels of
fishmeal and fish oil just before fish are marketed.
Phytoplankton sources of these essential fatty acids are
now commercially available for human consumption,
but they are not currently economically viable for use in
aquaculture feeds. Researchers also seek oil byproducts
from the biofuels industry, fish processing wastes and
discarded bycatch, worms, and insects to maintain the
health benefits of the final product, without depending
on fish oil. A major challenge for the marine finfish
aquaculture industry will be to continue to reduce its
dependence on wild fish for feeds and to identify more
sustainable feed ingredients, especially in replacement
of fish oil.
20.6 Marine Fishes in Aquaculture Figure 20.6 Farmed milkfish from the Philippines. The fish was
pulled from an ice bath used to chill fish immediately after harvest
Eight case studies of marine fish aquaculture are presented to preserve flesh quality. Source: Reproduced with permission
below. The goal is to describe species produced in signifi- from Henrylito D. Tacio, 2017.
cant volume (Table 20.1) but also to illustrate the diversity
450 Aquaculture Regional, seasonal, and annual variations in fry availa-
bility were major constraints to industry growth in the
subtropical Indo‐Pacific from Central America to past, but in the late 1970s significant advances were
Mexico, Hawaii, and as far south as southern Australia made by private hatcheries, research institutions, and
and New Zealand. government agencies in broodstock husbandry and
hatchery technologies for artificial fry propagation.
Natural spawning seasons vary among populations, but Milkfish farms in the Philippines, Taiwan, and Indonesia
generally extend over the warm months of the year. Ideal now purchase most of their fry from private hatcheries.
temperature for spawning is 20–33 °C with an optimum Hatcheries range from small backyard‐type facilities in
of 28 °C. Spawning occurs in outer reefs and is often cor- Indonesia to modern large‐scale facilities in Taiwan.
related with the new or full moon. In Taiwan, spawning Indonesian and Taiwanese hatcheries currently export
occurs from April to September in offshore waters of milkfish fry to neighboring countries.
around 30–40 m depth, and the female produces millions
of small eggs (1.1–1.2 mm in diameter) that hatch within 20.7.2.2 Broodstock Management
24 hr into yolk sac larvae (3.5 mm). As the pelagic larvae Milkfish broodstock are produced by growing juveniles
develop they migrate from offshore spawning grounds to in floating sea cages situated in sheltered bays or in deep
inshore areas, where young pre‐metamorphic larvae brackishwater ponds in the Philippines, or in large, land‐
approximately 14–21 dph (12–15 mm total length) aggre- based tanks supplied with flow‐through seawater, aera-
gate in intertidal areas and feed on plankton. After meta- tors, and automatic feeders in Indonesia and Taiwan.
morphosis at 28–35 days, juveniles become benthic algal They reach sexual maturity at an average body weight
feeders and are found in estuaries and mangrove lagoons, of > 1.5 kg in 4–5 yr in large floating cages and around
and occasionally move upriver into freshwater lakes. 8–10 yr in ponds and tanks. Broodstock are selected
Juveniles and adults are herbivorous or omnivorous and from hatchery‐reared fish to improve broodstock fecun-
eat a variety of food items, including detritus, microbial dity and growth rate. Broodfish are held at a sex ratio 1:1
mats, epiphytes and zooplankton. Subadult fish leave and fed a high‐protein diet supplemented with natural
these inshore environments as they approach sexual food such as freshwater fish and shrimp. In land‐based
maturity and return to the sea where they spawn. tanks, timing of gonadal development and sexual matu-
ration can be advanced by exposing fish to increasing
20.7.2 Aquaculture daylength under a long photoperiod regime.
Milkfish is well suited for aquaculture because they grow 20.7.2.3 Spawning and Egg Incubation
fast and they efficiently use natural foods as well as a For fish held in nearshore pens or cages, natural spawning
variety of supplemental feeds of plant and animal origin. (without hormonal intervention) occurs during the
They are relatively resistant to diseases and handling, natural spawning season at temperatures of 26–35 °C.
and tolerate salinities ranging from freshwater to hyper- Spawning fish have reduced appetite and increased court-
saline. The remarkable euryhaline ability allows milkfish ship behaviour, including chasing, leaping, and water‐
to be grown in a variety of systems, from inland brack- slapping from midday to early evening, with spawning
ishwater ponds to fish pens and cages situated in fresh- usually occurring around midnight. Captive broodstock
water lakes and reservoirs or in coastal estuarine and can spawn up to 4 times in one season. Female brood-
marine environments. stock of approximately 8 yr and 6 kg spawn 3–4 million
eggs in one season. Females continue to spawn large
20.7.2.1 Collection of Wild Fry numbers of eggs until they are 14–15 yr of age.
The milkfish aquaculture industry traditionally depended
on the collection of wild‐caught ‘fry’ for stocking fish Broodstock held in land‐based tanks have been
ponds. Following onshore migration, the young fry con- induced to spawn by hormonal manipulation. Milkfish
gregate along sandy beaches and mangrove areas and can have separate sexes (i.e., non‐hermaphroditic) and sex
be caught by fry‐gatherers using fine‐mesh nets. Fry col- ratio in natural populations is close to 1:1. Knowledge of
lection has historically been an important industry in the gonadal development stage is critical to hormone‐
coastal areas of the Philippines, Taiwan, and Indonesia induced spawning. Stage of ovarian development is
where large concentrations of fry could be found. Wild‐ determined by biopsy: a polyethylene cannula is inserted
caught fry were distributed to rearing pond operators into the ovary through the genital pore and used to
who grow the fish to a marketable size for sale to consum- extract a sample of ovarian tissue which is examined
ers. The traditional distribution system involved various microscopically. Administration of luteinising hor-
middlemen, including runners who transported fish, mone‐releasing hormone analogue (LHRHa) via a pellet
dealers and concessionaires who held fish for various implant or liquid injection induces spontaneous spawning
periods of time, and brokers who facilitated exchanges
among parties, but did not physically handle the fish.
approximately 48 or 24 hr after application, respectively. Marine Finfish Aquaculture 451
A mature female induced to spawn can produce 2 million
eggs/kg of body weight per year. Eggs produced through pond through separate inlets. Ponds are shaded with
hormone‐induced spawning show inconsistent fertilisa- black plastic to prevent larvae from exposure to direct
tion success relative to eggs produced through natural sunlight and excessive algal blooms.
spawning, probably related to the stage of ovarian devel-
opment at the time of hormone induction. Commercial Ponds are stocked with about 0.6–1.2 million fertilised
hatcheries rely mainly on natural spawning of brood- eggs to provide a starting density of 2–5 larvae/L. On day
stock as a simpler, more reliable option to obtain ferti- 2, Nannochloropsis sp. is introduced as greenwater. In
lised eggs. Taiwan, natural blooming phytoplankton from other
ponds is used as a source of greenwater. From day 3 to day
Eggs are collected by air‐lift collectors and the 8, larvae are fed oyster eggs to facilitiate first‐feeding, and
buoyant, fertilised eggs are incubated in cylindro‐ from day 5 rotifers Brachionus plicatilis are added.
conical tanks at 30–34 ‰ salinity and 26–30 °C. Aeration Artemia is not used, but eel feed, fishmeal, and artificial
is used to maintain dissolved oxygen levels and to keep microdiets may be provided in addition to rotifers as early
eggs suspended. At 28 °C, eggs hatch about 24 hr after as day 10. Fry are ready for harvest at 20–25 days at a
fertilisation. mean total length of 1.5 cm. In Taiwan, 0.2–0.6 million fry
are typically produced in a 200–300 m2 pond.
20.7.2.4 Larval Rearing
Milkfish fry are produced using two general methods: 20.7.2.5 Nursery Rearing
indoor intensive tank production used primarily in the Nursery operations vary according to traditional culture
Philippines and semi‐intensive outdoor pond produc- practices in the major producer countries. In the
tion used primarily in Taiwan. Large‐scale milkfish Philippines, milkfish nurseries are integrated with grow‐
hatchery operations usually condition and spawn brood- out facilities, where fry are first raised in a small com-
stock and rear larvae to the fry stages. Small backyard‐ partment of the larger grow‐out system. Fry are stocked
type hatcheries may purchase eggs or newly‐hatched at a density of up to 1000/L and feed on benthic algal
larvae from other facilities. mats and the associated microorganisms (known as
‘lab‐lab’ in the Philippines) which are encouraged to
In the intensive method, newly hatched larvae are grow on the pond bottom by application of fertilisers.
stocked into tanks (10–20 m3) at a relatively high density. Vertical‐net substrates are used to increase surface area
Live planktonic feeds are provided to the larvae begin- in the pond for growth of benthic algae. Nursery rearing
ning at 2 dph before the yolk sac is completely absorbed is also conducted in nylon mesh nets (hapas) suspended
at 120 hr after hatching. Beginning on day 1 and continu- inside a larger grow‐out enclosure such as brackish water
ing through 21 dph, the microalga Nannochloropsis ocu pond, or a pen or cage located in a lagoon or freshwater
lata is added. From 2 dph to 21 dph, larvae are fed rotifers lake. Feeds such as rice or corn bran, or commercial for-
Brachionus plicatilis at least twice per day. Beginning at mulated feeds are provided to supplement natural foods.
12 dph, Artemia nauplii are added. Except for freshly After 4–6 weeks, fry reach 5–8 cm and are stocked into
hatched Artemia, rotifers and older Artemia nauplii are the grow‐out ponds or pens.
enriched with commercial enrichment diets before they
are fed to the larvae to improve nutritional quality. In Taiwan, commercial hatchery and nursery systems
Enrichment results in better larval growth, resistance to are integrated, and milkfish fry are grown in large earthen
stress, and lower incidences of opercular deformities. At ponds or canvas or concrete tanks (300–400 m2 and
15 dph, an artificial microdiet is co‐fed with newly 1.5 m deep) and are stocked at higher densities of 2000/L,
hatched Artemia two to three times per day, and larvae or more. In Indonesia, backyard‐type nurseries consist
are completely weaned to artificial feeds by day 21. of much smaller canvas or concrete tanks (1–2 m3) and
Milkfish fry are harvested as early as day 21 at 14–16 mm are stocked at densities comparable to those used in
total length and are transferred to nursery ponds for Taiwan.
30–45 days of rearing before they are stocked in grow‐
out ponds. Distribution of fry from nursery to grow‐out facilities
involves transfers among multiple middlemen who
Hatcheries in Taiwan mainly use semi‐intensive pond‐ count, transport, and store fry for periods of up to a week
based production systems to produce milkfish fry. depending on demand. Fry are stored in 100‐ to 500‐L
Outdoor rearing ponds are 300–400 m2 in surface area containers and fed cooked chicken egg yolk, wheat flour,
with a depth of 1.5 m. The pond bottom is covered with or artificial microdiets. Survival of fry to the fingerling is
sand to maintain water clarity and to facilitate cleaning approximately 70%.
and harvesting. Airstones maintain oxygen levels, and
seawater, freshwater, and greenwater are supplied to the 20.7.2.6 Grow‐out to Marketable Sizes
Pond culture is the traditional type of milkfish production
system in the Philippines, Indonesia, and Taiwan. Shallow
452 Aquaculture months before transfer to grow‐out ponds as fingerlings
(2–7 cm; 1–6 g). At 4–6 weeks before stocking, ponds are
water (extensive) and deep water (intensive) pond cul- treated with teaseed cake powder, tobacco dust, or a
ture systems are used, which differ in the intensity of mixture of hydrated lime and ammonium sulfate ferti-
management of culture practices as well as the depth of liser to eradicate predators and pests. Ponds are drained
the pond. In the last 40 years, pen and cage culture has and dried, limed to control soil acidity, and then the
become increasingly popular in the Philippines. As will pond is tilled. During the process of gradually re‐filling
be seen, the basis for production ranges from natural the pond with water, fertilisers are applied to sustain the
productivity to formulated feeds, depending on culture growth of the lab‐lab as a natural food for the fish.
intensity. Inorganic fertiliser is applied at 1–2 week intervals to
maintain growth of lab‐lab.
In the 1980s commercial feeds were developed for
milkfish. In the 1990s, more efficient feeds were devel- After the nursery phase, fingerlings are stocked in
oped using feed extrusion technology, including float- grow‐out ponds at densities ranging from 1000 to 3000
ing feeds for cage and pen culture and sinking feeds for fingerlings/ha and production ranges from 300 to 900 kg/
pond‐ and tank‐based culture. Milkfish feeds for all ha per crop, or 600 to 1800 kg/ha per year. On most farms
stages from hatchery to marketable size (starter, grower, in the Philippines, fish reside in the same grow‐out pond
and finisher feeds) are commercially available (Lim until harvest. However, some farmers transfer fish
et al., 2002). through a series of three progressively larger ponds as
they grow to increase annual production to 2000–
20.7.2.7 Shallow‐water Ponds 4000 kg/ha. Commercial feeds are applied in shallow
In Indonesia, the Philippines, and other locations, milk- water systems when natural food is inadequate. Farmers
fish are typically cultured in shallow brackishwater monitor environmental conditions and exchange water
ponds to take advantage of tidal water exchange when weather conditions cause sudden changes in tem-
(Figure 20.7). A typical pond facility includes small nurs- perature and salinity or a depletion of dissolved oxygen.
ery ponds (0.1–0.4 ha) to raise the fry to fingerlings and In Taiwan, deeper overwintering ponds are constructed
large grow‐out ponds (~1–5 ha). Nursery ponds repre- next to the production ponds to hold fish that have not
sent one fourth to one third of the total pond area. Ponds reached marketable size by late autumn. These long,
are 40–50 cm deep and salinities vary from 10 to 35‰.
Fry are stocked in nursery ponds and are grown 1–2
Figure 20.7 Brackish water ponds adjacent to mangrove areas used for milkfish production in Tongatapu, Tonga. Source: Reproduced
with permission from Paul Southgate, 2017.
narrow ponds are built to water depths of 1.5–2.0 m and Marine Finfish Aquaculture 453
are covered with canvas or palm fronds and may be sup-
plied with heaters to protect fish against winter condi- 6–12 fingerlings/m2 depending on depth and water
tions which can lower water temperatures below 10 °C. current. A commercial formulated diet containing 27–31%
protein is fed 3 to 4 times daily and the fish reach harvest
Deep‐water Ponds size of 250–275 g in 4–5 months with 80–90% survival and
Deep‐water pond culture was developed as wetlands and yields of 1.5–5 kg/m2. Risks include pollution, weather,
mangroves became increasingly protected, land values and poaching. In some areas, over‐expansion of pen cul-
and labour prices increased, and shallow water pond cul- ture has led to self‐pollution and the spread of disease.
ture became less profitable. Mainly converted from
existing shallow‐water ponds, deep‐water ponds provide Cage Culture
greater water volume and production, as well as more Cage culture is conducted in freshwater lakes, estuaries,
stable water temperatures for production year around. and coastal marine waters. Cages range from 27 to
Semi‐intensive grow‐out ponds have a water depth of 1800 m3 for rectangular cages and from 1800 to 12 600 m3
1–3 m and fish are stocked at higher densities of 8000– for circular cages, and are constructed of polyethylene
12 000/ha. Deep‐water culture systems are managed net and various materials (e.g., bamboo, galvanised iron,
more intensively than shallow water systems. Fertilisers polyethylene pipe). They are staked in shallow waters or
are applied in the first 45–60 days of grow‐out to stimu- moored in deep water with floats and anchors. Small fin-
late natural productivity and artificial feed (minimum gerlings (5–10 g) are stocked at higher density in smaller
25% protein) is provided daily. In addition to tidal water nursery cages for 1–2 months before they are transferred
exchange, mechanical water pumps and paddlewheel to larger grow‐out cages. During the grow‐out stage, typi-
aerators are used to maintain water quality and safe oxy- cal stocking densities in stationary and floating cages are
gen levels for the fish. Under these semi‐intensive condi- 10–40 fish/m3. Survival ranges from 70–90% with yields
tions, annual production ranges from 5000–7500 kg/ha. of 3–20 kg/m3. Cages deployed in offshore areas with
greater water circulation can be stocked at higher densi-
Intensive deepwater pond cultures systems in Taiwan ties of 40–100 fish/m3 with yields of 20–35 kg/m3. A com-
use small (0.1–1 ha) ponds of 1–2 m depth. Fish are plete formulated feed (27–31% protein) is provided from
stocked at very high densities of > 20 000/ha and food stocking of the fish to harvest at a size range of 350 to
supply is entirely dependent on commercial feeds. Annual 500 g. Fish are fed two to three times daily by hand or
production can exceed 12 000 kg/ha. These intensive sys- automatic feeders. To develop marine cage farming of
tems require high capital investments for pumps and milkfish in the Philippines, mariculture parks have been
aerators as well as greater technical knowledge. established by the government which provide infrastruc-
ture and extension and marketing services to farmers.
Pen Culture
Pen culture was introduced in the Philippines in 1979 in 20.7.3 Diseases
the Laguna de Bay, a eutrophic lake with an average Milkfish are relatively resistant to infectious diseases and
water depth of 3 m, where fish farmers could take advan- relatively few serious epizootics have been reported.
tage of high primary productivity to meet the nutritional Bacterial (Vibrio anguillarum), mycotic, and parasitic
needs of milkfish. Pens enclose areas of the lake with nets (Lernea spp.) diseases have been associated with crowd-
supported by stakes. They vary in shape and may range ing, poor water quality, and handling stress. In overwin-
from 1 to 100 ha and typically consist of an outer barrier tering ponds in Taiwan, cold temperatures, crowding,
net and an inner enclosure net with finer mesh. and poor water quality conditions are sometimes associ-
Supplementary feeding is required when fish are stocked ated with disease. High mortality of hatchery‐reared
at higher densities or when natural food is depleted. Pen juveniles has been associated with the parasitic dinoflag-
operators in Laguna de Bay stock 30 000 to 50 000 finger- ellate Amyloodinium ocellatum, which causes erosion of
lings per ha. Small fingerlings (5–25 g) are purchased skin and gills at the sites of attachment. Mortalities have
from nurseries and are reared in small nursery pens until also been associated with opercular and gill membrane
40–50 g and then they are transferred to the grow‐out abnormalities which are likely related to nutritional defi-
pens where they reach market size (250–300 g) in 4 to 8 ciencies during the larval stages.
months with a survival rate of 60–80%. Yields ranges
from 4000 to 10 000 kg/ha. 20.7.4 Processing and Marketing
After harvesting, milkfish are marketed fresh or chilled,
In the mid‐1990s, pen culture was introduced into whole or deboned, frozen, or processed. In the
coastal intertidal rivers and lagoons in the Philippines Philippines, most frozen fish are exported to the USA as
with water depths of 2 to 7 m. In coastal waters, grow‐out
pens are smaller (500–1600 m2) and fish are stocked at
454 Aquaculture barriers were closed and fish were held in these lagoons
until they reached a marketable size. By the early 1970s,
milkfish bellies, backs, and heads and tail. Preservation fry availability was reduced due to overfishing, changing
methods have made it possible to export fish in quick‐ coastal conditions, and pollution.
frozen, dried, canned, bottled, smoked, or marinated
forms. Milkfish have numerous fine intermuscular bones Production of European seabass juveniles in hatcheries
that reduce palatability, but deboning machines or high started in the late 1970s, and by the 1980s, hatchery pro-
pressure cooking techniques are used to produce bone- duction had become a reliable technology in several
less milkfish products with higher market acceptance. Mediterranean countries. By 1992, aquaculture produc-
These popular products are sold fresh, smoked, mari- tion of European seabass using hatchery‐reared seed-
nated, or frozen for domestic consumption or for export stock surpassed 10 000 t, and by 2007, it surpassed
to the USA and EU. In the Philippines and Taiwan, imita- 100 000 t. Seabass production has steadily increased to a
tion seafood products (‘surimi’) are produced from peak of 156 450 t in 2014. Turkey led production with
minced milkfish. Taiwan exports processed and value‐ 74 653 t followed by Greece (32 142 t), Spain (16 722 t),
added products to the USA. Milkfish processing byprod- and Egypt (15 167 t). Croatia, Cyprus, France, and Italy,
ucts (viscera, head, fins, tail) are being studied for use in also produce significant quantities.
human or animal feeds. Indonesia exports hatchery‐
reared fry to the Asia‐Pacific region. 20.8.1 Biology and Life History
The European seabass (family Moronidae) is found in
To promote the safety of their milkfish products, major the eastern Atlantic in an area from Ireland and the
milkfish producing countries are addressing the food North Sea, south to Senegal. Its range extends across the
safety concerns of importing countries, including Hazard Mediterranean Sea into the Black Sea. It has an elon-
Analysis and Critical Control Point (HACCP) require- gated body with a large terminal mouth. It has a dark
ments during production, harvesting, and processing grey back with silvery sides fading to white on its abdo-
and traceability in the use of antibiotics and drugs. men (Figure 20.8). The fish may reach 15 kg. The
Taiwan uses eco‐labelling to promote the quality of pro- European seabass lives and feeds on or near the bottom
cessed milkfish products for export, and Indonesia certi- in coastal waters, including estuaries and lagoons. They
fies the health of fry exported to other Asian countries. are euryhaline and are found primarily in saltwater above
30‰ but can be found in dilute brackish water.
20.7.5 Industry Challenges
Milkfish compete with wild‐caught and imported fishery Spawning occurs in the winter in Mediterranean pop-
products and do not command a high farm gate price. As ulations and extends into spring in the Atlantic popula-
milkfish culture practices intensify and production tions. Spawning occurs at the mouths of rivers and
increases, farm‐gate prices are not likely to increase. estuaries where salinities are above 30‰. Planktonic lar-
Biosafety and quality control measures to satisfy importer vae develop at sea and move inshore as they grow. The
country requirements are increasing production costs. young develop in brackish water where they remain for
To sustain industry growth, production costs must be two summers. Sexes are separate with the average age to
reduced by improving feeds and processing technology. maturity being 4 years for females and 2 years for males
To increase domestic and export market demand, fur- in the Mediterranean and 5–8 years and 4–7 years and
ther diversification of products to meet changing gener- for females and males, respectively, in the Atlantic. In
ational food preferences and increasing international nature, they feed primarily on shrimp, molluscs, and fish.
product recognition and acceptance by different ethnic Biology and culture of European seabass are described in
groups will be important to the industry. Tidal fluctua- Vasquez and Mũnoz‐Cueto (2014).
tions related to climate change are anticipated to require
elevation of dikes of coastal milkfish ponds in the future. 20.8.2 Aquaculture
20.8 European Seabass 20.8.2.1 Broodstock
Wild‐caught and hatchery‐reared fish are used as brood-
European seabass have long been highly prized as food stock. Although wild‐caught broodstock are sometimes
fish in Europe and the Mediterranean. The fish histori- used to avoid inbreeding and to maintain natural genetic
cally were cultured in enclosed lagoons with other spe- lines, most hatcheries maintain their own broodstock
cies, including gilthead sea bream and mullet. Fry were and rarely recruit from wild stocks. Hatchery‐reared
trapped in lagoons during the annual spring migration broodstock are selected based on desirable traits.
by opening barriers made of nets, reeds, or cement to Selective breeding programs have been underway since
allow natural stocking of lagoons with fry. Once stocked, the mid‐1980s in France, Spain, Italy, and Israel to
Marine Finfish Aquaculture 455
Figure 20.8 European seabass. Source:
© Citron / CC‐BY‐SA‐3.0.
improve growth, morphology and carcass yield. Some ‘the lighted method’ similar to that used in larval culture
strains of European seabass have been maintained in of the gilthead sea bream and ‘the French technique’
captivity for more than six generations. characterised by an initial rearing period under darkness
and without rotifers. In ‘the lighted method,’ water tem-
20.8.2.2 Spawning perature in larval tanks is kept at 15–17 °C when stocking
Broodstock are maintained at a ratio of 2 males to 1 and is then gradually raised to 17–20 °C by 34 dph. A
female. Spawning tanks range from 1 to 20 m3 in volume long photoperiod of 18 hr light: 6 hr dark is maintained at
and most broodstock systems are recirculating systems a light intensity of 500 lux. European seabass larvae show
to allow better control of environmental conditions. better growth when raised at reduced salinities (25–
Gonadal development is triggered by decreasing tem- 26‰) from hatching to metamorphosis. However, most
perature and shortening daylength in the fall, and final commercial hatcheries use full strength seawater (36‰)
maturation and spawning occur in winter. Captive due to logistical issues of supplying brackish water.
broodstock spawn naturally in brood tanks, but voli-
tional spawning is unpredictable. Therefore, induced Larvae are fed rotifers and Artemia nauplii from 3
spawning is preferred. Broodstock can also be condi- dph, and prey concentrations are increased up to 12
tioned to spawn outside of the natural season by manip- dph. Microalgae (‘greenwater’) is added to the larval
ulating the photothermal regime. Human chorionic rearing tank from 3 dph onward using various species of
gonadotropin (hCG) or gonadotrophin hormone releas- live microalgae. Non‐viable microalgae are also pur-
ing hormone analogues (GnRHa) are used to induce chased as condensed pastes from various commercial
spawning. Spawning occurs when the water temperature suppliers. Dry formulated microdiet is introduced at 17
is approximately 14–15 °C, and the spawning season lasts dph. At 24 dph, the addition of rotifers and greenwater
for approximately 2 months with individual females ceases. By 34 dph, larvae are fed only enriched Artemia
spawning up to several times each season. metanauplii. Commercial enrichment media are used to
boost essential polyunsaturated fatty acids, vitamins,
Fertilised eggs (1.0–1.25 mm diameter) are incubated and amino acid levels in Artemia metanauplii. At this
in 100–250 L conical tanks. Gentle aeration is provided time, the post‐larvae are considered to be at the juvenile
to keep eggs in suspension. Eggs are incubated with flow‐ stage and can be transferred to the nursery system.
through seawater and at the spawning temperature of Typical survival through the end of the larval phase at
14–15 °C. Hatching occurs approximately 3–4 days after 43 dph is 50%.
fertilisation and the newly‐hatched larvae are 4 mm in
total length. After hatching, buoyant (viable) larvae are In the ‘French technique’ larvae are maintained under
separated from the sinking (non‐viable) larvae and are dark conditions or very low light levels for the first 8–10
transferred to the larval culture system. days after hatching. After this initial dark period, larvae
are exposed to light intensities of 500 lux and are fed
20.8.2.3 Larval Culture rotifers and Artemia nauplii until 20 dph and then
Larval rearing systems are either flow‐through or recir- enriched Artemia metanauplii until 42–45 dph.
culating. Larval culture techniques, including feeding Alternatively, some culturists omit rotifers and feed only
regimes and culture methods vary widely among hatch- enriched Artemia metanauplii after the dark phase.
eries. Two larval rearing methods are commonly used: Survival using this method is similar to the ‘the lighted
method’ and averages 50%.
456 Aquaculture in the diets with plant proteins, such as soybean meal,
maize gluten meal, and wheat gluten, which provide up
20.8.2.4 Nursery Culture to 30–40% of dietary protein. Feed conversion ratios vary
Juveniles are transferred from the larval culture system to greatly from 1.35 to 2.45, depending on feeding method
a nursery system from 43–45 dph at an average weight of (Kousoulaki et al., 2015).
80 mg. Only individuals with normally inflated swim blad-
ders are selected for transfer to the nursery. Fish are anes- Onshore Recirculating Aquaculture Systems
thetised and placed in 60‰ water. Fish with normal swim Recirculating aquaculture culture systems are increas-
bladders float, while those with non‐inflated swim blad- ingly used to raise European seabass because they allow
ders sink and are discarded. Under ideal culture condi- for greater control of culture conditions, which are highly
tions, 80–100% of juveniles have properly inflated swim variable in sea cage culture systems. Recirculating
bladders. Recirculating nursery systems are mainly used s ystems also mitigate user conflicts by moving fish pro-
during the nursery phase as they allow the greatest control duction facilities inland, away from the coast. Stocking
of environmental conditions. Water temperature is 18 °C densities in RAS can be as high as 40–70 kg/m3. Water
and is usually raised to 22 °C during the nursery period. temperature is maintained at 24–25 °C throughout
Initial stocking density varies from 1.5–4/L. Photoperiod culture, which accelerates time to market compared to
can vary from 14 hr light:10 hr dark to 24 hr light. Fish are sea cage in which fish are exposed to seasonal tempera-
fed enriched Artemia metanauplii at decreasing rates until ture changes. Fish grown in RAS reach a market size of
58 dph when Artemia feeding is stopped. Fish are fed a 400 g in 9–12 months.
commercial microdiet at 2‐hr intervals during the daylight
hours. High water flow is maintained to help flush excess 20.8.3 Marketing and Industry Challenges
feed from the culture tanks. Major markets for the European seabass are located in
southern Europe and extend as far north as the Baltic
20.8.2.5 Grow‐out Sea. Due to years of intensive culture the market is
Fingerlings are transferred from the hatchery to the grow‐ saturated for traditional whole fish (300–450 g).
out systems at approximately 1.5–10 g and 3–6 months Diversification into the fillet market, however, is slow
old. Market size of 400–450 g is reached in 9–24 months due to competition from less expensive fish species such
depending on grow‐out method and water temperature. as tilapia. Furthermore, the fillet market requires a larger
To minimise size variation and cannibalism, fish are fish (800–1000 g) leading to increased grow‐out times
graded two or three times during the grow‐out period. and production costs.
Sea Cage Culture Challenges facing European seabass aquaculturists are
Sea cages are primarily used for grow‐out of European the same as those facing the gilthead sea bream aquacul-
seabass fingerlings to market size. These systems range ture industry. In recent years, market prices have been
from nearshore operations in waters only a few meters depressed due to an increase in farm‐raised product. To
deep to open‐ocean facilities in waters over 40 m deep. add value to the market, growers are diversifying beyond
Cages vary in size up to 25 m in diameter and 10 m deep the whole fish market to other processed forms such as
and can float on the ocean surface or can be submerged fillets. Growing and marketing fish for the organic or
in the water column. Many types of commercial net pens sustainable markets is adding value over traditional mar-
or cages are used, ranging from simple wooden frames keting. Hatchery and grow‐out techniques are being
and barrel systems to sophisticated facilities such as steel streamlined to lower production costs, including devel-
platforms or submersible steel cages that can withstand opment of more effective artificial microdiets in replace-
harsh offshore conditions. The most widely used sea ment of live feeds and diets for grow‐out in sea cages that
cages are circular floating cages made with high‐density utilise alternative protein sources to fishmeal and other
polyethylene pipes. Final fish biomass densities in sea ingredients to reduce wastes.
cages can reach up to 20 kg/m3, depending on site‐spe-
cific environmental conditions. 20.9 Gilthead Sea Bream
Nearshore sea cage operations must compete for space Cultivation of the gilthead sea bream has been practiced
with other sea cage farms and with recreational and for centuries, first by the Etruscans and ancient Romans
urban use of nearshore sites. In many areas, inshore sur- in Italy. Wild juvenile fish were corralled into coastal
face cages have generated opposition from other indus- lagoons, along with European seabass, grey mullet and
tries, causing cage operations to be located further eel, and held until a market size was reached in 2–3 yr.
offshore in less protected open ocean environments. Fish
in sea cages are fed 1–2 times a day using commercial
pelletised feeds with varying protein (35–50%) and lipid
(10–26%). Progress has been made in replacing fishmeal
By the 1960s this form of culture waned due to lack Marine Finfish Aquaculture 457
of juvenile fish from overfishing and pollution. Methods
to control reproduction were developed in the late 1970s less than 30 m. Gilthead are omnivorous, feeding on
to early 1980s which led to large‐scale aquaculture pro- shellfish, crustaceans, and fish, and may be supple-
duction by the late 1980s. Aquaculture production has mented with seaweed and other marine vegetation. It is a
steadily increased, passing 1000 t in 1988 and 10 000 t in protandrous hermaphrodite: they start life as males and
2005. Total aquaculture production in 2014 was 158 389 t. reach sexual maturity at 2 yr and then transition to
In 2014, leading producing countries were Greece females at 33–40 cm. Adult fish migrate to the open
(50 687 t), Turkey (41 873 t), and Spain (16 915 t). The ocean to spawn from October to December in the north-
remainder was produced in Italy, Croatia, Cyprus, ern Mediterranean region and Atlantic Ocean and from
Portugal, France, and 19 other countries. The biology December to April in the southern Mediterranean
and culture of gilthead sea bream are summarised by region. After the first year of spawning, males start to
Pavlidas and Mylonas (2011). develop ovarian tissue. Depending on the male‐to‐female
ratio, males continue ovarian development and switch to
20.9.1 Biology and Life History functional females if females are lacking in the popula-
The gilthead sea bream (family Sparidae) is found in the tion. Males may also reabsorb the newly developed ovar-
Mediterranean Sea and along the east Atlantic from the ian tissue and continue functioning as a male.
British Isles to Cape Verde and around the Canary
Islands. Gilthead sea bream are rare in the Black Sea. The 20.9.2 Aquaculture
fish has an oval body that is deep and laterally com- 20.9.2.1 Broodstock
pressed. It has a steep forehead with small eyes and Both wild‐caught and hatchery‐raised fish are used as
mouth. The colour is silvery but can vary from reddish to broodstock. Wild‐caught broodstock are preferred on
nearly black. It has a large black blotch at the beginning some farms as they provide a more genetically diverse
of the lateral line and a bright yellow line runs between stock, but captive‐reared individuals are also used.
its eyes and on the stomach behind the pelvic fin Selective breeding programs have been underway in
(Figure 20.9). Greece and France since 2002 focusing on improving
growth rates, minimising deformities and increasing dis-
Gilthead sea bream are euryhaline, bentho‐pelagic fish ease resistance.
inhabiting brackish and marine environments including
coastal lagoons and estuaries. Adults are found around Wild‐caught fish are quarantined for observation and
seagrass beds and rocky or sandy bottoms from the surf treatment for external parasites, bacterial and fungal dis-
zone to 150 m depth, while young fish are found in waters eases. After quarantine, fish are transferred to the brood-
stock system, which is typically a recirculating or
flow‐through tank system. Wild‐caught fish are conditioned
Figure 20.9 Cage cultured gilthead sea
bream off the coast of Italy. Source: © FAO
Aquaculture photo library/F. Cardia.
458 Aquaculture immediately followed by release of sperm by males.
After fertilisation, viable eggs float to the surface while
to tank culture for at least 6 months. A sex ratio of 1 male: non‐viable eggs settle to the bottom. Floating eggs
2 females is best. Because gilthead sea bream are her- (1.0 mm diameter) are collected for incubation in the
maphroditic, sex ratios are closely monitored to ensure hatchery.
ratios are not skewed toward predominantly female over
time. Fish may be conditioned at salinities lower than full 20.9.2.2 Egg Incubation and Larval Culture
strength seawater of around 30‰, but salinity must be Conical tanks with a volume of 100–250 L are stocked
maintained at 35‰ during the spawning period. with fertilised eggs and hatch approximately 42‐hr post‐
fertilisation at 16–19 °C. The newly‐hatched larvae are
Gilthead sea bream are asynchronous spawners and 2.5–3.0 mm in length and lack differentiated organs, eyes
spawn 20 000–30 000 eggs/kg over an extended 4‐month are rudimentary, and the mouth is undeveloped.
spawning season. This output requires substantial physi- Development of sensory organs and mouth are com-
ological energy to sustain. Feeding and nutrition are cru- pleted by 5 dph. Larval first‐feeding is reached by 3–4
cial to broodstock health and reproductive success. To dph when the yolk supply is exhausted. At this time, the
maximise egg production and quality, a high‐quality mouth, anus, gut, and most internal organs are fully
commercial diet specifically formulated for maturing developed and functional. Initial mouth gape at first
fish is fed starting 1–2 months before the spawning sea- feeding is 250 µm. The gas bladder is inflated around
son and continuing until a month after spawning ceases. 7–10 dph.
This special broodstock diet is rich in fatty acids DHA
and EPA, and both dry and moist diets are used. During Intensive larviculture culture of gilthead sea bream is
the non‐breeding periods, broodstock are fed a less characterised by high stocking densities, controlled envi-
expensive maintenance diet that is similar to a natural ronmental conditions, and the addition of exogenous
diet, including frozen fish, crustaceans, and molluscs. A feeds, including microalgae and zooplankton. At 3 dph,
high‐quality commercial dry‐pelleted diet is also co‐fed microalgae is added to the culture tank (‘greenwater’)
with the frozen diet. several times throughout the day. Depending on the
hatchery, various species of live algae are grown and
In nature, gonadal development in gilthead sea bream used, and commercially‐produced non‐viable algae
is stimulated by decreasing day length and temperatures, pastes of some of these species are also used. The most
and spawning occurs around the winter solstice. In cap- common feeding regime for gilthead sea bream is similar
tive broodstock, the timing of gonadal development and to those used for many marine finfish, with feeding pro-
maturation of broodstock is controlled using photother- gressing from rotifers to Artemia nauplii, and then
mal manipulation to obtain in‐season or out‐of‐season enriched Artemia metanauplii. Survival through the lar-
spawning. Commercial hatcheries use accelerated or val stage averages 30%.
extended artificial photothermal regimes to shift the
spawning season to 3, 6, and 9 months outside of the 20.9.2.3 Nursery Rearing
natural spawning season to obtain year round spawning. By 45 dph, larvae are transferred from the larval rearing
tanks into larger nursery rearing tanks. At this stage, fish
In the early 1970s, captive females could be condi- have completed metamorphosis and resemble the adults,
tioned to undergo ovarian development through the but are still reliant on live enriched Artemia metanauplii.
final stages of yolk deposition (i.e., vitellogenesis), but The larger tanks allow for continued growth, while the
such females did not complete final oocyte maturation, system can accommodate the higher feed load of the
ovulation, and spawning in captivity. Captive males, on weaning process from live onto artificial feeds. Circular
the other hand, completed sperm development and pro- nursery tanks that range from 10–30 m3 are used and are
duced viable sperm. Early attempts to induce spawning supported by either heated flow‐through seawater, or a
using injections of hCG or GnRHa did not produce con- recirculating filtration system. Larvae are introduced to a
sistent results. However, changing the delivery method dry diet in the larval rearing tanks, but are fed Artemia at
of GnRHa from a single injection to a sustained‐release a low feeding rate, which is gradually reduced as the dry
pellet implant produced reliable spawning over several diet is increased until addition of Artemia ceases by 60
months. Currently, gilthead sea bream hatcheries use dph. At this stage, fingerlings are fully weaned to a dry diet
photothermal manipulation and natural, voluntary and are fed at a rate of approximately 5% of wet body
spawning to obtain fertilised eggs. However, sustained‐ weight daily. The daily ration is fed 8 times a day at 2‐hr
release GnRHa pellet implants are used if reliable spawn- intervals throughout the day when the lights are on. Final
ing is desired from specific individuals. stocking density in nursery tanks can reach as high as
20 kg/m3. With proper care and grading, survival during
Under either natural or hormone‐induced spawning,
volitional spawning occurs in the broodfish tank at dusk
or early evening, daily for up to 4 months. Preceding
spawning, ovulated females swim rapidly and then
release eggs near the water’s surface, and this is
the nursery phase is around 90%. Fish are transferred from Marine Finfish Aquaculture 459
the nursery to grow‐out systems at approximately 5–10 g.
20.9.3 Marketing and Industry Challenges
20.9.2.4 Grow‐out As sea cage production increased through the 1980s
Grow‐out of fingerlings to marketable sizes was tradi- and 1990s, market prices for gilthead sea bream fell by
tionally conducted in shallow lagoons and extensive 60% in the early 2000s due market saturation. Efforts to
flow‐through tank systems. This type of culture has rebuild the market by better production planning, mar-
mostly given way to intensive forms of grow‐out systems ket support, and promotional support have helped
to maximise efficiency and profits. Most grow‐out is restore better market prices. Markets have been shift-
conducted in floating cages in the Mediterranean. Cages ing from whole fish to fillets, which are causing farmers
are usually located in protected or semi‐protected coastal to diversify their product, including production of
areas in water at least 5‐m deep. Coastal land for sea larger fish for the fillet market, which involves longer
cages has become limited due to competition with other grow‐out times. Efforts to refine culture practices are
groups such as the recreational and tourism industries, also leading to more efficient production and therefore
which is leading to more regulation of the sea cage indus- better profitability. These include improving feed effi-
try. Therefore, sea cage culture is moving offshore where ciency, increasing juvenile quality through selective
more robust cages are needed to handle the more breeding, automation, and better biosecurity and health
dynamic environment. management. Currently, profitability of sea bream pro-
duction is strong with stabilised harvests leading to a
Fully weaned fingerlings (10–30 g) are transferred firming of market price. Efforts to develop new export
from weaning tanks to sea cages. Stocking densities market areas in North America and the Middle East
target harvest biomass densities of around 15–20 kg/ have led to more outlets and may stimulate increased
m3 but can reach 30–40 kg/m3 depending on site‐spe- production in the foreseeable future.
cific conditions of water flow. Fish are fed commercial
pelleted diets, typically 45–50% protein and 20% lipid 20.10 Yellowtail Amberjack
(Koven, 2002). Feed is administered 1–2 times daily.
Feed conversion ratios in sea cages range from 1.5–2.0. Yellowtail amberjack (also called Japanese amberjack)
In floating cages, fish are raised from fingerling stage has been an esteemed food fish in Japan for centuries
to market size (350–400 g) in approximately 12–16 (Figure 20.10). Aquaculture has developed rapidly due to
months. Variability in growth rates in floating cages is its high market value and superior quality as sushi and
typically due to inconsistent temperatures over the sashimi. Yellowtail aquaculture is the largest and most
seasons, which can vary from 11 °C in the winter to successful marine fish farming industry in Japan, but is
23 °C in the summer. also important in Korea and China. Usually, yellowtail is
cultured in coastal areas in floating net cages.
Land‐based tank farms allow more intensive culture
at higher densities than in sea cages. Production sys- Recent efforts have been made to develop aquaculture
tems vary greatly from flow‐through to recirculating of other amberjacks in floating sea cages in different areas
aquaculture systems. Tank construction, shape, and of the world, including yellowtail kingfish (Seriola
size vary greatly between farms, with volumes of up to lalandi) in Japan and Australia, longfin yellowtail (S. rivo
100 m3. Intensive tank systems enable high production liana) in the United States, greater amberjack (S. dumer
volume with minimal land used. Flow‐through systems ili) in Japan, the Mediterranean and Vietnam, and Pacific
use concrete or plastic tanks supplied with a constant yellowtail (S. mazatlana) in North and Central America
high flow of new water. Tank sizes vary greatly among (Sicuro and Luzzana, 2016).
grow‐out facilities and range from tens to several hun-
dreds of cubic meters. Intensive flow‐through tank cul- 20.10.1 Biology and Life History
ture allows stocking densities to reach 25 kg/m3, and Yellowtail (family Carangidae) range from the continen-
pure oxygen is added to maintain safe dissolved oxygen tal shelf of the East China Sea to the coastal waters of
levels for the fish. Hokkaido, both in the Japan Sea and the Pacific. It has an
elongated body that is slightly compressed laterally and a
Recirculating aquaculture systems allow fish to be longitudinal yellow stripe. In nature, yellowtail grow to
raised at very high biomass densities ranging from 40 kg in weight, but commercial market size is much
15–45 kg/m3. Feeds are the same as those used in sea smaller (1–2 kg). Yellowtail is a fast‐swimming, pelagic,
cage systems. Compared to floating sea cages, more effi- carnivorous fish that feeds on smaller fish (such as mackerel
cient feed conversions (as low as 1.3) are attained in tank and sardines) and squid.
culture. Under controlled water temperature (24 °C), fish
are raised from fingerling stage (5–10 g) to commercial
sizes of 350–400 g in approximately 1 yr.
460 Aquaculture
Figure 20.10 Print of a woodcut ‘A Shoal
of Fishes’ made by Utagawa Hiroshige in
1832 showing yellowtail amberjack and
pufferfish. Source: Hiroshige [Public
domain], via Wikimedia Commons.
Yellowtail spawn offshore in southern Japanese waters achieved mainly due to the difficulty in securing healthy
from southern Kyushu to the Chugoku area of the Sea of broodstock as well as low‐quality larval production. A
Japan, and the main spawning season occurs from dated, but useful, review of yellowtail aquaculture is pro-
February through June. Young larvae (1.5 to 15 cm total vided by Nakada (2002).
length) attach to drifting seaweed and are transported by
currents to the north. The juveniles migrate north to 20.10.2.1 Broodstock Management
Hokkaido and reach sexual maturity in 3–5 years. Adults and Controlled Breeding
migrate south to spawn. Throughout the year different Yellowtail for broodstock are usually captured by set‐
sizes of yellowtail can be caught in coastal waters of nets and fed frozen fish, moist pellets, or commercial
Japan. The common name of Japanese yellowtail varies soft‐dry pellets for about 2 yr in net cages. Females are
with size. In Japan, yellowtail that are < 50 g are called tagged and transferred from the net cage to indoor circu-
‘mojako,’ between 50 and 5000 g are ‘hamachi,’ and lar or rectangular spawning tanks. In captive yellowtail
those > 5000 g are ‘buri.’ broodstock, photoperiod and water temperature are
manipulated to accelerate the gonadal maturation in
20.10.2 Aquaculture females. However, hormone injections are usually
Successful yellowtail culture started in 1927 in the required to stimulate final ovarian maturation, ovula-
Kagawa prefecture of Japan using wild‐caught juvenile tion, and spawning. Ovarian tissue is sampled by insert-
fish reared in nearshore enclosures, and aquaculture ing a cannula into the genital pore of a female and
production began to increase rapidly in the 1960s. sampled eggs are examined microscopically for ovarian
Currently, commercial‐scale production of yellowtail maturity and to determine egg diameter. To induce
juveniles in hatcheries has not been developed to a level spawning, a single dose of hCG is injected into the dorsal
comparable to that of other cultivated marine fish in muscle of both sexes. Females can also be ovulated by a
Japan such as red sea bream and Japanese flounder (olive single implantation of a cholesterol pellet containing
flounder). Most fry for stocking sea cages are obtained GnRHA. About 2 days after the administration of hCG,
by capture of wild fry but regulations by the Japanese fish begin to spawn volitionally in the brood tanks at
Fisheries Agency limits the number of wild‐caught fry 18–20 °C. Eggs are collected from the spawning tanks
that can be caught in each Japanese prefecture to pre- using a fine mesh net. The eggs may also be stripped
serve natural yellowtail population. Therefore, to pro- from the female to a clean container and milt is added
duce large numbers of juveniles to meet the demand of and mixed for about 5 min. Floating eggs (1.1–1.3 mm
farmers, better techniques for artificial production of fry diameter) are transferred to incubation tanks.
are being developed. However, wild‐caught fry remains
the major source of seedstock. Unfortunately, hatchery‐ 20.10.2.2 Larval Rearing
produced seed have a high percentage of body deformi- At 20 C̊ , eggs hatch in 36 hr and first feeding larvae are
ties, and reliable mass juvenile production has not been about 4.5 mm. First feeding begins at 3 dph and transfor-
mation to the juvenile stage occurs at 50–55 dph at
45 mm total length. The standard rearing protocol for Marine Finfish Aquaculture 461
yellowtail larvae includes feeding rotifers Brachionus
plicatilis from the first day of feeding and enriched and offshore. Fish are grown for 1–2 months on artificial
Artemia nauplii from 12 dph. Rotifers and Artemia feed and minced frozen fish until they reach 50–100 g
nauplii are enriched with n‐3 highly unsaturated fatty when they are stocked into grow‐out enclosures.
acids EPA and DHA, which are required for optimal Advanced juveniles are raised and sold to grow‐out
growth and larval vitality. Cultured (or wild) copepods farmers by private cooperative fishermen. Wild yellow-
are sometimes fed during the post‐larval stages. At tail fry is also imported in Japan from the Republic of
20 dph, artificial formulated microdiets are introduced Korea, China, and Vietnam.
and are co‐fed with live feed until 50–55 dph when lar-
vae are completely weaned to artificial feeds and are 20.10.2.4 Grow‐out
considered juveniles. In the hatchery larvae do well at Commercial yellowtail grow‐out culture occurs in sea
20–22 °C and at a salinity of 33–36‰. Usually, 300–500 cages (Figure 20.11). Depending on water temperature,
fish/m3 (20 mm total length) can be produced in the mozako (fish < 50 g) are stocked from April through July.
hatchery with 5–10% survival. However, after meta- The stocking densities of yellowtail in a grow‐out system
morphosis high mortalities of hatchery‐reared yellow- vary with the grow‐out stage of the fish, the type of cul-
tail fingerlings and early juveniles have lowered the ture system, cage‐site conditions such as water exchange
average survival rates through the advanced juvenile rates, dissolved oxygen and water temperature. Yellowtail
stage to 0.5–2.0%. grow rapidly in net‐pens. From the fry stage Japanese
yellowtail can reach 1.5–2 kg within one year and 4–7 kg
20.10.2.3 Capture and Nursery Rearing in about 2 yr. Optimum rearing water temperature is
of Wild Fry 20–27 °C and salinity is 30–36‰.
Due to insufficient fry production in hatcheries, aqua-
culture of Japanese yellowtail is mainly dependent on the In the past, yellowtail raised in net pens were
fry supply from wild. The spawning of wild yellowtail in mostly fed trash fish and bycatch discarded from the
the offshore waters around Shikoku and Kyushu occurs catch of other fisheries. Currently, feed for yellowtail
from late February to April. Just after spawning, larvae in Japan consists of both extruded pellets and moist
(less than 15 mm total length) are transported by the cur- pellets. Usually moist pellets contain commercial
rents to nearshore coastal areas. Mozako, the young yel- fishmeal (12.5%), fish oil (5%), and 70% raw/frozen
lowtail, are typically caught with a small purse seine net, whole fish such as Japanese anchovy and sardines.
or with a set net and are kept in small nursery cage nets Moist feeds are usually prepared on site at the grow‐
until they can be sorted for growing. During April‐June, out farm by mixing minced raw fish and dry ingredi-
yellowtail fry 5–15 cm in total length are caught by com- ents and binders. Due to the recent development of
mercial fishery cooperatives from 8–25 km offshore. extruded pellets for yellowtail, feed quality has
After grading, wild‐caught yellowtail juveniles (<10 g) improved and production costs have been lowered.
are reared in small net pens located both near the coast Extruded soft‐dry pellets containing 44–55% crude
protein and a wide range of lipid (6–20%) are used
for yellowtail culture, with feed conversion ratios as
good as 1.2.
Figure 20.11 Yellowtail amberjack in a sea
cage. Source: Hiroshige [Public domain],
via Wikimedia Commons.
462 Aquaculture 20.10.3 Marketing and Industry Challenges
A market size of about 2–5 kg is the target of most
Various substitutes for fishmeal such as soybean Japanese yellowtail growers, while some grow the fish
meal, corn gluten meal, and meat meals have been to 7–8 kg for processing into fillets. In 2014, total yel-
used to replace the amount of fishmeal in yellowtail lowtail aquaculture production in Japan was 135 800 t.
feeds without adverse effects on fish performance Fish are usually fasted before harvesting to evacuate
(Nguyen et al., 2015). Taurine supplementation is nec- their digestive tracts. Rapid killing, complete bleed-
essary for diets that contain high levels of alternative ing, filleting, and proper packaging and refrigeration
protein sources for yellowtail over long feeding periods of fish provide a product of excellent quality. Live fish
due to the deficiency of taurine in plant protein are usually supplied to upscale Japanese restaurants,
sources. The requirements of dietary lysine and while fresh and frozen fish are supplied to the whole-
methionine were established as 1.66% and 1.11% of the sale stores and supermarkets, and processed fillets are
dry diet of juvenile yellowtail in the presence of 0.31% delivered directly to individual restaurants and homes.
cysteine. Requirement for EPA and DHA highly unsat-
urated fatty acids was estimated to be about 2% of the The critical areas for future growth of the yellowtail
diets. Carnivorous yellowtail cannot utilise significant aquaculture industry in Japan are a stable supply of fry,
amounts of carbohydrates. disease control, and development of more cost‐effective
and environmentally‐friendly artificial diets. Further
20.10.2.5 Diseases development of technologies for artificial propagation of
Yellowtail are more vulnerable to infectious diseases healthy juveniles in hatcheries is critical.
at water temperatures above 28 °C. The major diseases
reported in yellowtail are iridovirus infection, also 20.11 Red Sea Bream
known as viral splenic virus, yellowtail ascite virus,
vibriosis, streptococcus infection, fungal infection, Red sea bream is one of the main cultured marine fish
and flatworm infection. Rapid removal of sick or dead species in Japan and Korea. Commercial culture of red
fish from affected pens and cessation of feeding of raw sea bream began in 1965 using embankment ponds or by
fish‐based diets are the first steps in the preventing partitioning small bays into culture units using levees,
further spread of disease. Proper amounts of antibiot- pilings, or netting. Production increased dramatically
ics are uniformly added to the feed to treat some bac- during the 1970s when net‐cage technology was intro-
terial infections. Vaccines give some protection duced. Red sea bream is a high‐quality, sashimi‐grade
against pasteurellosis caused by Photobacterium fish with high market value and is an important symbol
damsela. in Japanese culture used in various celebrations such as
New Year’s and weddings (Figure 20.12). Its unique red
Figure 20.12 Red sea bream in a market
in Ueno, Japan. Source: Gideon 2007.
Reproduced under the terms of the
Creative Commons Attributions license,
CC‐BY 2, via Flickr.
colour is considered to be a good luck symbol in Japan. Marine Finfish Aquaculture 463
Red sea bream is known as ‘Madae’ in Japan, and
‘Ch’amdom’ in Korea. Red sea bream juveniles are also pellets are prepared by mixing raw fish with formulated
produced in Japan and Taiwan for stock enhancement mash (e.g., squid meal, fishmeal, and vitamin mixture).
purposes. Kagoshima Bay in southern Japan has been a Environmental manipulation and hormonal injection are
major site for release of cultured red sea bream into the normally used to induce red sea bream to spawn in cap-
environment for stock enhancement purposes. The suc- tivity. Environmental manipulation consists of lowering
cess of stock enhancement program of red sea bream has water salinity to 20–25‰ and then adding seawater to
been reported in the Kagoshima area of the southern simulate the rising tide with final salinity near 30–32‰.
Japan where the annual catch of red sea bream has Concurrently, water temperatures in the tanks are
increased significantly since stock enhancement was decreased from 31–32 °C to 27–28 °C to simulate fish
started in the 1960s (Kitada and Kishino, 2006). migration toward inshore waters after rain.
20.11.1 Biology and Life History To induce spawning, broodstock are held in a pre‐
spawning tank for 2 months and females are inspected
Red sea bream (Sparidae family) is a demersal, carnivo- for ovarian maturity by measuring egg diameters. Males
rous fish widely distributed in the coastal waters of the with running milt are chosen and selected females are
northwest Pacific, the east coast of China, Taiwan, and injected with a mixture of homogenised carp pituitary
southern Japan. Red sea bream can usually be found at gland and hCG. Fish spawn 36 hr after injection at 18 °C.
depths of 10 to 50 m; however, they may occur at depths If no spawning occurs, a second injection is administered
of up to 200 m. They spend most of their time over rocky to the female 48 hrs after the first injection. The fertilised
substrates, but also on softer bottoms and reefs. In eggs (0.8–1 mm) are collected from the spawning tanks
nature, red sea bream feed on various live fish and ben- using a fine mesh net. As an alternative, eggs may be
thic invertebrates, including echinoderms, worms, mol- stripped from the female to a clean container and then
luscs, and crustaceans. Their body is oval shaped and milt is added and mixed with the eggs, followed by fil-
compressed laterally. The upper profile of the head of red tered seawater to activate the sperm. About 90% of ferti-
sea bream is convex with a bulge above the eye. The lised eggs hatch at the peak of the spawning season, and
upper body and head are dark violet whereas the sides a female red sea bream of 3–7 years age can produce 1 to
and belly are silvery. In freshly caught fish, the body con- 4 million eggs during one spawning season.
tains many bluish dots. Adults reach 8–9 kg. The repro-
ductive season starts from March to May in the Kyushu 20.11.2.2 Larval Rearing
region and from April to June in the Inland Sea of Japan Newly hatched larvae are transferred to floating larval
when adults migrate into shallow areas of the ocean to rearing tanks made of synthetic fibre cloth that are sus-
spawn. In nature, spawning occurs at water temperatures pended in a larger concrete tank. The optimum water
from 15 to 22 °C. temperature for larval rearing is 18–20 °C. For the first 3
days the larvae subsist on their yolk sac. Feeding is
20.11.2 Aquaculture started at 4 dph when the digestive organs are formed,
and the yolk sac is absorbed. During the larval stage, oys-
In Japan, the technology of red sea bream seed produc- ter eggs, copepods, and enriched rotifers and Artemia
tion was developed in the 1960s and by the mid‐1980s nauplii are used as feeds. From 30 dph, fish are fed com-
the intensive grow‐out production system of red sea mercial formulated microdiets and are fully weaned to
bream had been developed. It is mostly cultivated around microdiets or minced fish by 40–45 dph. Recently, micr-
Kyushu Island and in the Seto Inland Sea, and the main odiets are also co‐fed with live feed as early as 10 dph and
production method is nearshore cage culture. this allows weaning to artificial feeds at an earlier stage.
Automated systems for delivering live feeds and microdiets
20.11.2.1 Broodstock Management to the larval rearing tanks and automated bottom sweep-
and Controlled Breeding ing systems for removing debris from these tanks have
For broodstock purposes, wild‐caught, or cage‐reared been developed for intensive mass larviculture of red sea
adults averaging 3–5 kg are held in floating cages or con- bream in Japan. Survival to 30–35 dph (12–13 mm total
crete tanks. The fish reach sexual maturity at 3 yr of age, length) is 40–50%.
and equal numbers of males and females are used. In
most hatcheries, fresh and frozen trash fish, shrimp, krill 20.11.2.3 Nursery Rearing
and squid, and moist pellets, and artificial commercial Red sea bream fry about 10–50 mm in total length are
broodstock diets are offered to broodstock fish. Moist weaned in tanks or in small sea cages with a mixture of
minced fish or artificial microdiets and starter diets con-
taining high protein (about 55%). Small square net‐cages
are commonly used for nursery rearing and are installed
464 Aquaculture red sea bream. Fishmeal can be completely replaced in
the diets of juvenile red sea bream by soybean meal sup-
inside larger net or sea cages. Post‐larvae from 30–40 plemented with fish solubles, squid meal and krill meal
dph (10–15 mm) are cultured for about 30–50 days until without negative effects on fish growth (Kader et al.,
they reach the fry stage (60–80 mm total length). Survival 2012). Many kinds of grow‐out diets for red sea bream
from stocking to the fry stage averages 30%. have been developed in recent years. Carotenoids, vita-
min E, and vitamin C are also included in the diets to
In addition to hatchery production of red sea bream enhance the red or bright pink colour, which is a valued
post‐larvae by private hatcheries, seedstock ranging from market characteristic.
fry to fingerling stages (25–100 mm total length) are col-
lected by commercial fishermen from the sea using seine Red sea bream ignore leftover feeds at the bottom of
nets. These wild‐caught seedstock are temporarily the cages. As a result, longer feeding durations and
stocked in floating net cages until they are transferred to higher feeding frequencies are necessary to ensure that
their grow‐out cages. Although there has been significant the right amount of feed is administered in the cages. It
progress in producing red sea bream fry in the hatcheries is also important to avoid overfeeding to prevent pollu-
in Japan, about 10% of the fry used for grow‐out produc- tion of local waters. From the fry stage (60–80 mm total
tion of the red sea bream are wild‐caught. length) red sea bream grown in sea cages reach 600–
800 g in 18 months, 1 kg in 24 months, and 1.2–1.5 kg in
20.11.2.4 Grow‐out 36 months.
Red sea bream are raised from fingerling to marketable
sizes in cages, pens or impoundments; the net‐cage sys- 20.11.2.5 Diseases
tem is the most popular in Japan. At about 3–4 months Red sea bream in all phases of culture are susceptible to
post‐hatch (60–80 mm, or larger) fry are stocked in the viruses, gram‐negative bacteria, and ectoparasitic dino-
grow‐out system, although fish as small as 30 mm flagellates, ciliates, monogeneans, and nematodes. Red
(~2 months post‐hatch) can be stocked in net pens with sea bream iridoviral disease (RSIVD) is a major cause of
appropriate sized mesh. Currently, some farmers are mortality in farmed red sea bream (Kawato et al., 2016).
raising red sea bream in net cages placed in deeper off- Outbreaks of RSIV disease have occurred every summer
shore areas where stronger currents produce fish with in Japan since the virus was first reported in 1990.
thicker, firmer flesh with a texture preferred for sushi Currently, effective formalin‐killed commercial vaccines
and sashimi and where conditions give red sea bream a for RSIVD are available for red sea bream. Oral adminis-
bright red colour. tration of Lactobacillus probiotics has also shown posi-
tive effects on the growth, feed utilisation, health
Red sea bream perform well at temperatures between condition, and immune system of the red sea bream.
20–28 °C; feeding decreases at temperatures below 20 °C
and stops at 10 °C. Both dry artificial feed and wet ground Hatchery‐reared red sea bream have a high incidence
trash fish are used to raise red sea bream on commercial of body deformities, particularly in the vertebrae.
farms in Japan. Trash fish are ground at the grow‐out site Lordosis has been a serious problem in the culture of red
using a meat grinder and is sometimes mixed with dry sea bream larvae and typically occurs in larvae with
ingredients such as algae (Spirulina spp.), gelatinised deflated swim bladders because larvae are unable to gulp
starch and vitamins. Wet fish are effective as a dietary air at the water surface to inflate their bladders when
component for improving fingerling performance; how- they reach 4–4.5 mm length (10–15 dph). Providing ade-
ever, the use of wet fish in cage culture has significantly quate amounts of dietary vitamin A and highly unsatu-
decreased due to development of better formulated rated fatty acids in live feed and the application of
diets. The major nutrient requirements of the red sea microdiets during weaning from live feeds play an
bream are well studied and formulated dry pellets are important role in avoiding deformities and improve the
commercially available for red sea bream grow‐out in swimming activity of red sea bream larvae.
Japan (Koshio, 2002). Commercially available grow‐out
diets contain 45–55% crude protein, with 15–20% lipid. 20.11.3 Marketing and Industry Prospects
The amino acid profile of red sea bream juvenile muscle Red sea bream are marketed in Japan in live, fresh, and
tissue is used as a reference for dietary amino acid frozen forms. Fish marketed live command a price
requirements for this species (Alam et al., 2005). The 30–60% higher than frozen fish. In China, live red sea
fatty acids EPA and DHA should be 1% and 0.5%, respec- bream of about 2 kg or larger are exported to Japan.
tively, of the diet. It is essential to supplement taurine to Recently, red sea bream producers and processors have
low‐fishmeal diets for red sea bream due to the defi- promoted consumption of fish in ways other than sushi
ciency of taurine in plant protein sources. and sashimi, targeting markets beyond Japan, China, and
Strategic combinations of plant proteins and terrestrial
animal by‐products could improve the fishmeal replace-
ment levels to 50–60% in juvenile and 70–90% in yearling
Korea. Due to high demand, the fish are also shipped fro- Marine Finfish Aquaculture 465
zen and as processed fillets to wholesalers in Southeast
Asia, the Middle East, the USA, and Europe. In Japan, 20.12.1 Biology
production of red sea bream is the second largest fish The cobia is an elongated sub‐cylindrical fish with dark
culture industry, after yellowtail amberjack. However, brown colouration on its dorsal side and a white ventral
total production of cultured red sea bream in Japan has side. Along its lateral region, the colouration is paler
declined from around 80 000 t in 2004 to 56 861 tons in brown. Juvenile fish have a noticeable black band that is
2013 as the number of farms have decreased and the approximately the width of the eye and extends along the
costs of feed and of seed from hatcheries have increased. length of the body from the snout to the base of the
Consequently, the unit price of cultured red sea bream caudal fin (Figure 20.13). This dark line may become
has been rising as production volume has declined. pronounced in adult fish during the spawning season.
Further progress is needed on production of healthy Cobia are the only representative of the genus
juvenile red sea bream in hatcheries, development of Rachycentron and are also the only member of the family
cost‐effective feeds, and development of environmen- Rachycentridae. Common names include black kingfish,
tally‐sound technology for both offshore aquaculture in ling, lemonfish, black salmon, crabeater, and black
sea cages and land‐based aquaculture using closed recir- bonito. They can attain a weight of 78 kg and can live up
culating aquaculture systems. to 15 yr in the wild.
20.12 Cobia In the wild, cobia form large, offshore congregations
during an extended spawning season that generally
Cobia are found in most of the world’s major oceans occurs during the spring and fall in subtropical and trop-
except the mid and eastern Pacific. They are more ical regions. However, cobia found in temperate regions
abundant in temperate and tropical waters in the have a distinct summer spawning window. It is estimated
Atlantic throughout the Caribbean Sea and in the Indo‐ that females can spawn as many as 30 times during the
Pacific areas off India, Japan, and Australia. There is a season and release from 400 000 to 5 million eggs
limited commercial fishery for cobia, possibly because depending on the size of the fish. Females reach matura-
they only form small schools and are found near under- tion during their third year while males mature after only
water or floating structures. Because of the small com- two years of age. The larvae are planktonic.
mercial fishery, there is no established international
market. Instead, the fish are more commonly caught by Juvenile and adult fish appear to migrate according to
recreational anglers, but are prized for their firm‐tex- water temperature but are generally found between 16 to
tured flesh. 32 °C. Data from capture fisheries studies indicate that
cobia prefer temperatures above 20 °C and will migrate
Aquaculturists have been attracted to the potential of to warmer waters during cooler months. They also
cobia culture by the fish’s rapid growth rate (up to 6 kg appear to seasonally move north or south along coast-
within the first year) and the firm‐textured, mild flesh line, or migrate out to the open ocean in search of suita-
that is suitable for the higher valued markets. Most of the ble water temperatures. They are relatively tolerant of a
world production of cobia is concentrated in China wide range of salinities and have been found in salinities
(88.5%) and other Asian countries in the region. between 22–44‰ but have been cultured in salinity as
Worldwide production increased steadily during the low as 5‰.
early 2000s, but reached a peak in 2012 and has declined
slightly since then, mostly caused by lower production in 20.12.2 Aquaculture
Vietnam. Outside of the Asian region, cobia production 20.12.2.1 Reproduction
has increased in the Caribbean area and in South The first reported spawning of cobia in captivity was in
America — principally in Brazil. the early 1990s in Taiwan Province of China, which led to
the establishment of several commercial hatcheries by
Because current methods for cobia culture involve the the end of that decade. Current practices for almost year‐
use of cages or pens in shallow offshore waters, countries round spawning involve temperature manipulation
with extensive coastal areas have traditionally been the (optimum range of 23–27 °C) of ponds or tanks to
first to attempt industrial production of this fish. encourage volitional spawning. Some hatchery managers
Attempts at land‐based tank culture, either in flow‐ have used hCG injections or GnRHa implants to induce
through or in RAS, have received some attention from and coordinate spawns, which usually occur within
researchers, but production from these kinds of systems 12–36 hr after injection or implant. Adult fish are stocked
is minor relative to the production from cages. at a 1:1 sex ratio or sometimes 2:1 (males:females) at
densities from 4–6 fish/100 m2 in ponds to 6–7 fish/m3
in tanks. The small (1.2–1.4 mm diameter) eggs float in
466 Aquaculture
Figure 20.13 Cobia grown in an offshore sea cage. Source: Reproduced with permission from Daniel Benetti, 2017.
the water column and can be harvested using specially dph when the fish are around 180 mm in length and
designed egg collectors placed on the outside of the weigh 30 g. At this time, they can be transferred to
tanks. Eggs hatch within 24–30 hr of spawning depend- another set of nursery cages, ponds, or tanks.
ing on water temperature. Recently hatched fry will
absorb their yolk sac and be ready for feeding about Some hatcheries employ a semi‐intensive ‘greenwater’
3 dph (Benetti et al., 2010). technique where larvae are stocked into small (<5000 m2)
ponds and allowed to graze on the natural zooplankton
20.12.2.2 Larval Culture blooms that result from the addition of fertilisers, which
Intensive culture of cobia larvae, as with most marine stimulate the growth of microalgae such as Chlorella
fish, requires small live prey during the first 25–30 days spp. Although this technique is simpler and lower in cost
of culture. Initial feeds during the first 4–5 days after than the intensive tank method, the ability to control live
hatching include enriched rotifers Brachionus plicatilits food availability is limited and diseases and pathogens
or copepod nauplii. Subsequently, slightly larger enriched are more difficult to control.
Artemia metanauplii are fed until the fish can be weaned
onto dry feeds around day 30 post‐hatch. Cannibalism Final survival in both intensive and semi‐intensive sys-
becomes a major problem during the weaning stage, so tems can vary considerably between 5–30% and seems to
hatchery personnel manage this issue by transferring the depend on stocking density. In general, lower densities
fish to a second tank or pond and grading the fish to decrease cannibalism, and therefore improve final sur-
reduce size variation beginning about 45 dph until 75 vival. Cobia stocked at densities greater than about 2
fish/L may show slower growth and higher incidence of
cannibalism.
20.12.2.3 Nursery Marine Finfish Aquaculture 467
Cannibalism is a major challenge during the nursery
phase of production. To improve survival, production lipid levels, ingredient digestibility, and methionine and
managers periodically grade the fish by size while trans- lysine requirements have recently been conducted.
ferring them to progressively larger tanks as they grow. However, a complete diet specifically formulated for
Co‐feeding of live feed along with dry formulated feeds cobia has not been developed.
improves the ability of the fish to eventually wean onto
dry feeds. Fish in nursery ponds or tanks are fed 5–6 Efficient farming operations for cobia involve the
times/day at 5% of body weight per day. Feeding rate is grouping of many cages in close proximity to reduce
gradually reduced to 2–3% as the fish grow from 30 g to transportation and logistics challenges. Large‐scale pro-
200 g in the nursery tanks. duction could potentially impact coastal areas where the
water currents may not allow for timely removal of nutri-
20.12.2.4 Grow‐out ents emanating from these cages. Studies in Asia are
Although hatchery and nursery methods may differ beginning to consider the carrying capacity of different
between different countries (ponds and tanks; greenwa- water bodies used for cobia farming in relation to the
ter and intensive live‐feed production), grow‐out meth- nitrogen and phosphorus produced by these farms.
ods worldwide are almost exclusively dominated by net
pens or sea cages in nearshore or offshore locations. There has been limited research on the use of land‐
Cages or pens differ in size and method of construction. based tank systems for the culture of cobia. Recirculating
Floating pens or cages can vary between 1000–2000 m3, systems have been evaluated in the USA but only at the
and submersibles as large as 3000 m3 are used. Cobia pre- research and pilot scales. The economics of this type of
fer water with dissolved oxygen concentrations above production system have not yet been determined.
5 mg/L, therefore, a suitable site with adequate move-
ment of oxygen‐rich water is needed to ensure good sur- Initial investment cost to establish an offshore farming
vival and growth. Cobia prefer water temperatures above operation is high. Nearshore farms reduce capital invest-
26 °C. ment because the farms are located in more sheltered
areas where there is less hydrodynamic energy. Offshore
From the 30 g fingerling stage, fish can reach 6–10 kg locations offer the benefit of added dilution and disper-
within 1–1.5 years, depending on stocking rates and sion of wastes, but entail greater operating costs because
water temperature. Final densities at harvest are from of the need to transport supplies over greater distances
10–15 kg/m3. Females grow faster than males and are by boat. Regardless of farm location, feed costs remain
both longer and heavier within each year class. Overall the highest single operational expense, and economic
survival as high as 90% during grow‐out has been profitability of cobia cultured in cages is largely depend-
reported, but diseases can dramatically affect survival. ent on feed costs. Several studies from different areas
Cultured cobia are noticeably shorter and fatter than around the world have reported feed costs as high as
their wild counterparts. It is also common to observe 92.2% of the operational costs. An economic study of
high levels of intraperitoneal fat and fatty livers in cul- cobia culture indicated that productivity below 6.3 kg/m3
tured fish. or a survival rate below 65.5% would render a cobia farm
unprofitable (Quiroz de Bezerra et al., 2016).
In Asian countries, fully weaned juveniles (about 200 g)
are fed commercial pelleted feeds, typically containing 20.12.2.5 Diseases
about 42–45% crude protein and 15–16% lipid. In the There are a wide variety of bacteria, viruses, and para-
Caribbean, some cage culture farms use feeds with sites that infest cultured cobia. Bacteria such as Vibrio
higher protein (50–53%) and lower lipid (10–15%). Feed alginolyticus, Vibrio parahaemolyticus, Photobacterium
is applied 6–7 days per week starting at about 2% of body damselae subsp. Piscida can cause mortality at most
weight per day and declining to about 0.5–0.7% body stages of production and are generally treated with
weight/day. Overall feed conversion ratio for the entire antibiotics. A vaccine is being developed to treat
production period is around 1.5, which is considered Photobacterium spp. and is showing some efficacy in
good. Some research on the replacement of the fishmeal controlled challenge studies. Viral infestations such as
component of cobia diets suggest that up to 100% of the Viral Nervous Necrosis (VNN) have been reported in
fishmeal can be replaced with soybean meal and supple- 3–4 kg fish in Malaysia and lymphosistis is caused by an
mental taurine. Because fishmeal is a major cost compo- iridovirus that has been reported in the nursery stages.
nent of cobia diets, replacement with the lower cost Neither virus has an effective treatment apart from dis-
soybean meal would help reduce production costs. infection of the system and quarantine of infected fish.
Additional research on other aspects of nutrition and
feeds development for cobia, such as optimal protein and Several parasites have been reported to afflict cobia at
various stages of production. Principal among these is
Amyloodinium sp. a parasitic dinoflagellate sometimes
called marine velvet disease because of the golden sheen
it causes on the skin of the fish. Amyloodinium is
468 Aquaculture Figure 20.14 Atlantic halibut (Hippoglossus hippoglossus) in the
Aquarium du Québec. Source: Photograph by Cephas (Own work)
particularly visible on the gills and can cause inflamma- [CC BY‐SA 3.0 (http://creativecommons.org/licenses/by‐sa/3.0)],
tion that reduces the ability of the fish to remove oxygen via Wikimedia Commons.
from the water. Fish exhibit a coughing behaviour or
flare out their operculum in an effort to improve oxygen flounder family include the winter flounder Pseudo
uptake. Common treatments for most of these parasites pleuronectes americanus and Atlantic halibut Hippo
involve the use of copper sulfate or formalin baths com- glossus hippoglossus (Figure 20.14) from the northwestern
bined with freshwater dips. Other less commonly Atlantic coast. Members of the large‐tooth flounder
reported parasites are leeches (Zeylanicobdella aruga family include the summer flounder Paralichthys denta
mensis), or copepods (Caligus sp.). Since open pens or tus and the southern flounder P. lethostigma from the
sea cages are commonly used for cobia production, the eastern USA Atlantic coast, P. olivaceus (also known as
use of bath or dip treatments poses special logistical hirame or Japanese flounder in Japan, and bastard hali-
challenges that require the temporary removal of the fish but or olive flounder in Korea) from the north‐western
to administer these treatments and then stocking them Pacific Ocean, and Chilean flounder P. adspersus and
back into the original cage. small‐eye flounder P. microps from North of Peru to the
central Chilean coast. In California halibut P. californicus
20.12.3 Markets from the Pacific USA Coast and Baja California in
Cobia farming is still in its infancy, but it has become Mexico, left and right‐eyed individuals are equally com-
an important marine fish within the last 20 years. Since mon. The greenback flounder Rhombosolea tapirina is
there is a very small commercial fishery for cobia, vir- found in southern Australia and New Zealand. The
tually the entire world market relies on cultured prod- scopthalmid family contains the turbot (Scophthalmus
uct. Global production of cobia reached a peak in 2012 maximus; Figure 20.15) distributed in European waters
at approximately 51 000 t. Production has declined from the Mediterranean Sea and Black Sea to the Baltic
slightly during the past few years. Production in 2014 Sea and Norwegian coast. The Soleidae family includes
was 40 000 t and the major producing countries were Senegalese sole Solea senegalensis found in coastal
China (35 563 t; 88.2% of total production), Vietnam waters of southern Europe and West Africa and common
(1 761 t; 4.4%), Panama (1 459 t; 3.6%), Taiwan Province sole Solea solea found in the northern Atlantic and the
of China (1 395 t; 3.5%), and Colombia (150 t; 0.4%). Mediterranean Sea.
Prices for cobia vary according to size and region, with 20.13.1 Biology
markets in Taiwan Province of China enjoying higher Flatfish are marine demersal carnivores found in all of
values for the larger fish (8–10 kg) sold whole. The the world’s oceans in cold, temperate, and tropical seas,
smaller fish (6–8 kg) sold whole or headless are the ranging from shallow bays to deep‐water habitats, with
preferred size for markets in Japan, while US markets most species found in habitats ranging from the near-
prefer fillets. shore to depths of about 100 m on the continental shelf.
The Atlantic halibut is exceptional, occurring at depths of
20.13 Flatfishes over 2000 m. Most of the cultured species use near shore
Flatfishes are marine or brackish water fishes in the
Order Pleuronectiformes. They include many species
with important recreational and commercial fisheries.
Commercial landings for most species peaked from the
1920s to 1950s and then declined to only a fraction of
their maximum catch by the 1990s. In addition to strin-
gent fishing regulations, research on culture for food and
for stock enhancement was implemented in response to
declining fishery landings and the expectation that aqua-
culture would help to reduce fishing pressure and rebuild
natural populations.
Flatfish of interest in aquaculture come from six fami-
lies: Pleuronectidae (righteye flounders), Bothidae (left-
eye flouders), Paralichthyidae (large‐tooth flounders),
Rhombosoleinae (greenback flounders), Scopthalmidae
(turbots) and Soleidae (true soles). Members of the righteye
Figure 20.15 Turbot in Pairi Daiza Aquarium, Brugelette, Belgium. Marine Finfish Aquaculture 469
Source: Photograph by I, Luc Viatour [GFDL (http://www.gnu.org/
copyleft/fdl.html), CC‐BY‐SA‐3.0 (http://creativecommons.org/ demersal eggs 0.80 mm in diameter. Total fecundity in
licenses/by‐sa/3.0/) or CC BY‐SA 2.5‐2.0‐1.0 (http:// flatfish is high, ranging from 400 000 to 5 million eggs
creativecommons.org/licenses/by‐sa/2.5‐2.0‐1.0)], via Wikimedia per female, with an average of 1.0–2.0 million eggs/kg
Commons. female body weight. Fecundity of large Atlantic halibut
females is lower at 50 000–160 000 eggs/kg. At hatching
feeding grounds as nurseries for the first 2 months to 2 yolk‐sac larvae range in length from 1.7–2.0 mm in
years of life before migrating to offshore spawning areas. Chilean flounder to 3.0 mm in turbot.
A unique characteristic of the group is the change Many flatfish inhabit estuarine conditions for part of
(metamorphosis) from symmetric larvae inhabiting the their life cycle and are able to tolerate a wide range of
water column to asymmetric juvenile flatfish favoring temperatures and salinities. Southern flounder adults
the benthic habitat. Metamorphosis presents unique have been captured in a range of near 0 to 36‰ salinity.
challenges to the flatfish culturist. Among other extreme The winter flounder is freeze resistant, able to synthesise
morphological, physiological and behavioural changes, antifreeze proteins and secrete them into their blood
one eye translocates to the other side of the head and during the winter. Optimal growth temperatures range
positions itself next to the eye on the other side. During from 7–14 °C for Atlantic halibut, from 14–19 °C for tur-
metamorphosis, the upper (ocular) side becomes pig- bot, and 21–24 °C for the summer and southern floun-
mented, and the lower (anocular or blind) side light‐col- der, and 20–25 °C for P. olivaceus (olive or Japanese
oured, and there are changes in dentition and fin flounder).
placement. Metamorphosis can be a difficult period in
flatfish culture. Adult flatfish are almost always lacking a 20.13.2 Aquaculture
swim bladder. Flatfish aquaculture is presented in detail by Daniels and
Watanabe (2010).
With the exception of the Atlantic and Pacific halibut
which reach sizes up to 4.7 m length and 320 kg live 20.13.2.1 Broodstock
weight, flatfishes are not large fish. In the wild, average Most flatfish hatcheries use either wild‐caught or F1 gen-
length and weight at age 3 years range from 30 cm and eration broodstock. Wild‐caught flounder may be cap-
400–600 g for the greenback flounder to 30–40 cm and tured in nets or by hook and line, but wild‐caught fish are
2–3 kg for turbot. All of these flatfish show sexual dimor- slow to take food and do not easily wean to formulated
phism in growth, with females growing faster and reach- diets. For biosecurity, new broodstock flounder are quar-
ing larger size than males. antined in a separate facility and carefully screened for
diseases such as nodavirus (Nervous Necrosis Virus),
Flatfish are generally serial spawners, producing multi- which can be transmitted to eggs, larvae, and juvenile fish.
ple batches of eggs during the spawning season in inter- Informal selection of broodstock from F1 and F2 popula-
vals of 3–4 days. Most species produce small pelagic eggs tions based on growth or appearance is conducted on
ranging from 0.8 to 1.1 mm in diameter. Eggs of the some farms and research facilities. In Japanese hatcheries,
Atlantic halibut, however, are relatively large (3 mm) and where flounder fingerlings are used for stock enhance-
float close to the ocean floor during development. The ment as well as for commercial grow‐out, wild‐caught
winter flounder, on the other hand, produces adhesive flounder are used for spawning in order to maintain the
genetic diversity of juveniles produced for restocking.
Domestication of flatfish for farming has reached its
highest level of sophistication in the turbot farming
industry, where research on applied genetics is con-
ducted by commercial farms, and little or no information
exists in the public domain. Broodstock management
programs for turbot were established since the early to
mid‐1990s in France and Spain using both wild and
farmed fish of genetically distinct lineages. The selection
of broodfish is a subjective process depending on the
expertise of hatchery technicians who prioritise normal
body shape and colour, vigorous swimming and feeding
behaviour, no history of diseases during grow‐out
and representative of as many different populations as
possible.
470 Aquaculture are maintained under different photothermal regimes to
obtain fertilised eggs all year round.
Broodfish Holding Systems
Tanks of 2–4 m3 are used for broodstock of some flatfish Spawning
species (e.g., greenback flounder), while larger tanks of Natural (spontaneous) spawning without hormone
15–40 m3 are used for larger species (e.g., Atlantic hali- induction is observed in many species of flatfish. Some
but). Flow‐through or recirculating seawater are used for species (e.g., P. olivaceus, California halibut, Chilean
holding broodstock for most species, but recirculating flounder) spawn large numbers of fertilised eggs in out-
tanks are preferred as they permit better control of tem- door tanks without hormonal intervention. Natural
perature than flow‐through tanks. Low light levels, tem- spawning of wild‐caught adult broodstock improves
perature regimes that mimic the natural environment, after acclimation to captivity for at least two seasons.
and good water quality are used to help ensure successful
acclimation of broodstock. For turbot, natural spawning In some flatfish species, hormone‐induced spawning
occurs exclusively in large, deep tanks with a sandy sub- provides better control over the timing and availability of
strate using broodstock adapted to captivity for at least 2 embryos and is a more reliable method for stocking
years. However, when fish are manipulated for hormone hatcheries. When hormone‐induced strip‐spawning is
induction and strip‐spawning, smaller tanks are used. used to initiate ovulation, knowledge of the stage of ovar-
Sex ratios are usually about 1:1. ian development is required to gauge receptivity to hor-
mone treatment and the timing of strip‐spawning.
Broodfish Nutrition Ovarian biopsy using a polyethylene cannula is used, but
The natural diet of flatfish includes a wide variety of fish, backlighting (i.e., using a ‘light table’) is an inexpensive
molluscs, and crustaceans. For most species of flatfish, and effective method that takes advantage of the flat-
there is inadequate knowledge of the nutritional require- fishes’ body conformation to visualise gonadal develop-
ments of broodstock to develop formulated feeds, and ment non‐invasively.
replacing raw or frozen ingredients is therefore a con-
tinuing problem, especially for wild‐caught flatfish, For the Atlantic halibut and for the turbot, females are
which are difficult to wean onto prepared diets. induced to mature and ovulate through photothermal
Hatchery‐raised broodstock are generally fed a commer- manipulation, and strip‐spawning and artificial fertilisa-
cial pelleted feed containing a minimum of 55% protein tion are used to obtain viable eggs. For most species of
and 12–15% lipid which are usually fortified with vita- flatfish, artificial insemination of eggs is typically per-
mins and proper ratios of essential fatty acids EPA, DHA, formed following strip-spawning of females that have
and ARA. Broodstock that have been acclimated to been induced to ovulate using GnRHa administered in
spawn in captivity and weaned to formulated feeds are saline injections or through a sustained‐release choles-
valuable and are difficult to replace. terol‐cellulose pellet, but carp pituitary extract and hCG
have also been used successfully. To supply fertilised
In Asia, moist pellets are manufactured on‐site by mix- eggs on demand, spawning is synchronised among
ing a powdered commercial premix with trash fish prior broodstock by implanting a desired number of females
to extrusion through a feed processor. In China, turbot with oocytes meeting a critical minimum average
broodstock are usually fed chopped trash fish and moist diameter.
pellets boosted with commercial or farm‐specific mix-
tures (e.g., vitamins and essential fatty acids). Fresh or Flatfish males often produce very small quantities of
frozen fish in broodstock diets is a suspected vector for milt and can be difficult to strip. In Atlantic halibut,
pathogens such as viral diseases as nodavirus (VNN) and GnRHa implants are effective in synchronising spermia-
viral hemorrhagic septicemia (VHS) which may be trans- tion, but in southern flounder, hormone implants or
mitted to eggs, larvae, and juveniles. This has increased injections are ineffective, so photothermal conditioning
the impetus for research on broodstock nutritional is the most effective method for stimulating spermiation.
requirements as a basis for formulated dry pelleted diets. In the turbot farming industry in Europe, use of cryopre-
served sperm is reducing the need to maintain male
Photothermal Conditioning broodstock.
To achieve out‐of‐season spawning, accelerated photo-
thermal regimes, in which the annual photothermal Egg Collection and Incubation
cycle is compressed from 12 months to only 4–10 Flatfish eggs are incubated in upwelling tanks to main-
months are effective in advancing maturation and tim- tain them in suspension. In P. olivaceus, hatching rate is
ing of spawning of flatfish, so that spawning may be higher in a darkened room. Live eggs are typically disin-
achieved in less than 12 months to produce viable fected before hatching and eggs are typically incubated at
embryos over a majority of the year. In commercial temperatures near spawning conditions to optimise yolk
hatcheries for turbot in China, 5–6 groups of b roodstock utilisation efficiency, but temperature is increased by
several °C within a few days of hatching to accelerate Marine Finfish Aquaculture 471
metabolism, feeding, growth, and survival.
proportion of hatchery‐reared fish. This is attributed to
20.13.2.2 Larval Culture both genetic and nutritional factors. While these pigment
System Design abnormalities do not affect flesh quality, these fish are
Semi‐intensive larval culture was originally used for com- commercially inferior. For stock enhancement, fish with
mercial production of turbot in Europe and halibut in hypomelanosis (lack of pigmentation on the ocular side)
Norway through the mid‐1990s, where newly‐hatched lar- are more susceptible to predation. The causes of these
vae from indoor incubators are transferred at low densities abnormalities remain unclear but may be related to essen-
to large tanks (50 m3) previously conditioned to provide tial fatty acid nutrition, overall energy intake, iodine and
prey organisms to sustain the fish until harvest, or to out- thyroid hormone levels, photoperiod, and temperature.
door bag enclosures and fed wild plankton and Artemia.
These systems are simple to operate, but zooplankton Flatfish hatcheries universally use microalgae for
availability was unreliable, risk of exposure to pathogens intensive larval rearing (‘greenwater culture’), with algae
was greater, and production was unpredictable. pastes and algae substitutes preferred over live algae,
which is labour and space intensive and can potentially
Intensive larval culture is the preferred method used in harbour pathogens. Greenwater is beneficial during the
commercial hatcheries for flatfish where larvae are raised pelagic larval stages to enhance first feeding success,
in indoor tanks under controlled environmental condi- equalise distribution of larvae, and improve larval
tions and live prey and formulated feeds are added daily growth, and promote normal pigmentation patterns. For
to the tanks. At a research scale, flatfish larvae have been greenwater culture, a variety of microalgae and species
successfully raised in small tanks (3–15 L), but tanks of combinations in either live or preserved form are used.
1000–4000 L are typical for pilot production. Research in Atlantic halibut has indicated that powdered
clay is a cost‐effective alternative to microalgae, suggest-
In European turbot hatcheries, flow‐through seawater ing that the physical attributes (light‐shading) may be
systems are generally used, but water can be partly re‐ more important than the biological (immunostimulant,
used. Turbot hatcheries in China use flow‐through sys- antimicrobial, micronutritional) benefits to larvae of this
tems, using natural seawater or saline well water species.
pretreated by mechanical filtration, aeration, UV disin-
fection and temperature adjustment. In these flow‐ Food and Feeding
through systems, sand‐filtered seawater is adjusted to In intensive hatcheries, larvae are generally fed live prey,
optimum temperature (18–19 °C) and then pumped into including rotifers and Artemia nauplii, before weaning to
a head tank before distribution to the larviculture sys- formulated diets. Despite their small initial size, flatfish
tem. Saline well water from deep aquifers is preferred larvae have a sufficiently large mouth gape to feed readily
because it is devoid of pathogens. Researchers are turn- on rotifers and both L‐type or S‐type rotifers are fed,
ing increasingly to RAS for flatfish hatcheries, which usually twice daily.
provide more control of water quality and more consist-
ent production. Inadequate nutrition during the larval and metamor-
phic stages in flatfish may affect normal development,
Hatchery Protocols including eye migration and pigmentation, and survival.
In Atlantic halibut, the period from hatching to first The nauplii and copepodids of calanoid (Calanus) cope-
feeding, can last up to 50 days depending on tempera- pods are a preferred first food for larvae, but since they
ture. During this period, yolk‐sac larvae are held in are not easily produced at a large scale, their biochemical
upwelling cylindro‐conical incubators and typical sur- composition is used as reference for live prey enrichment
vival rates range from 50 to 80%. Strict temperature con- products and for the formulation of compound diets.
trol is used to avoid developmental abnormalities (e.g., Feeding copepods during a critical period (‘copepod
jaw deformities) and mortality. Larvae are kept in near or window’) can enhance normal development, pigmenta-
complete darkness because they are strongly attracted to tion, and survival, while minimising demand. For Atlantic
light during later stages. Salinity affects the buoyancy of halibut, which have a relatively large mouth size,
fertilised eggs and yolk‐sac larvae as well as the growth researchers have achieved good survival, pigmentation
and survival of early larvae before metamorphosis, and and eye migration with an Artemia diet using commer-
salinities above 28‰ are preferred for the larval rearing cially available enrichment products.
of most flatfish species.
Before use, rotifers and Artemia are nutritionally
Most cultured flatfishes exhibit abnormal pigmentation enriched to satisfy the requirements of larvae for highly
(pseudoalbinism on the ocular side and hypermelanosis unsaturated fatty acids, taurine and vitamins using either
on the blind side), and incomplete eye migration in a homemade enrichment mixtures (lipids, proteins, vita-
mins and minerals), or different commercial emulsions.
Specific requirements for flatfish larvae have been shown
472 Aquaculture potentially be minimised in flatfish hatcheries by syn-
chronising metamorphosis and settlement through the
for ARA, EPA, and DHA, and live prey are nutritionally use of thyroid hormones which regulate metamorpho-
enriched before feeding. Normal eye migration and body sis in flounder species.
pigmentation in many flatfish are dependent upon
proper amounts and ratios of these essential fatty acids, In Japan, survival of P. olivaceus to 3.0 cm total length
especially DHA and the ratio between DHA and EPA. In is usually higher than 60% and sometimes exceeds 80%,
turbot, the DHA: EPA ratio should be at least 2:1. and similar survival (50–70%) is obtained in Korean
hatcheries for the same species. Overall survival from
A deficiency in vitamin A (a precursor of the retinal egg through metamorphosis typically averages 40% for
pigment rhodopsin) disrupts neuroendocrine signalling southern flounder. In Europe, survival rates in turbot
from the eyes to the brain to produce melanocyte stimu- hatcheries are relatively low, ranging from < 10% to > 30%,
lating hormone and subsequently melanin synthesis, and the critical periods are at first‐feeding and between
resulting in abnormally pigmented flatfish with lower 12–15 dph, when Artemia feeding begins. A mean
market value. Enrichment of rotifers and Artemia with annual survival rate of 20% to 90 dph (1–2 g) is consid-
highly unsaturated fatty acids or vitamin A has been ered to be economically acceptable for commercial tur-
effective in preventing pigmentation anomalies on the bot hatcheries. In China, survival rate of turbot from
ocular side. newly hatched larva to juvenile (2 cm total length) varies
from 0–40% among hatcheries and averages 10–20% in
To ensure that rotifers and Artemia presented to the large hatcheries.
larvae are freshly enriched and that nutrients are not
catabolised, larvae are fed 3 to 4 times daily, flushing 20.13.2.3 Nursery Rearing
uneaten rotifers and Artemia from the tanks before add- System Design
ing a newly enriched batch. In European turbot hatcher- Depending on species and location, different strate-
ies, enriched prey are slowly metered into larval rearing gies are used to optimise growth and survival during
tanks using peristaltic pumps to ensure satiety, while the nursery period, which ranges from the post‐meta-
avoiding overfeeding. Flatfish hatcheries consistently use morphic stages (1–10 g) to the size at which fish are
long photoperiods of 18 to 24 h, feeding throughout the stocked into production tanks (20–150 g) for grow‐
photophase to produce higher larval growth rates and out to marketable sizes. Nursery culture of flatfish is
survival to metamorphosis than those attainable under conducted in land‐based tanks situated in a green-
ambient lighting conditions. Recommended light inten- house or in an industrial building in proximity to the
sities vary with species, and the size, depth, and colour of hatchery.
the rearing tank, density of greenwater used, as well as
type of light (natural or artificial) affect illumination to In Europe, turbot juveniles leave the hatchery at 3–4
the larvae and prey. months (1–3 g) and are raised in a nursery up to 5–20 g,
but sometimes up to 80–100 g, for a period of about 3–6
Larval rearing through metamorphosis generally months. Flow‐through tanks were traditionally used, but
requires from 30–40 days in cultured flatfish, but requires RAS systems using high stocking densities (500–1 000
as many as 80 days at 5 °C in winter flounder. Newly met- fish/m) enable better control of environmental factors,
amorphosed flounder are weaned onto dry feeds (200– biosecurity, and heating and pumping costs. To maxim-
400 µm, 52–55% protein and 12–15% lipid) by co‐feeding ise use of space in nurseries for turbot, shallow RAS
a micro‐pelleted diet (150–450 µm, 52–55% protein and raceways (0.25‐m deep) of various sizes are stacked in
12–15% lipid) and Artemia for 2–3 weeks and gradually tiers of 3 or 4. Closed RAS systems are also commonly
reducing the Artemia ration during this period. In some used for nursery production systems for commercial
flatfish (e.g., Atlantic halibut, California halibut), post‐ hatcheries in Japan.
metamorphic fish wean quickly, and extended co‐feed-
ing with Artemia is unnecessary. Nursery Protocols
Temperature control is critical for flatfish growth, but
During the process of weaning from live feeds, flatfish optimum temperature may decrease with size. In turbot,
larvae are generally fed microdiets in excess to increase the optimal temperature range decreases with size from
the opportunity to feed, leaving large amounts of uneaten 16–22 °C for 10‐g fish to 16–19 °C for 50 g fish. An
feed on the tank bottom, which can impair water quality. ontogenetic decline in temperature optima also occurs in
Removal of settled organic matter is crucial. Atlantic halibut and in P. olivaceus.
Grading and Harvest Sex differentiation of flounder is believed to be strongly
Growth variation during the hatchery phase is consid- influenced by temperature around the time of metamor-
erable, and as flounder metamorphose and settle to the phosis, with high culture temperatures favouring male
bottom, cannibalism of smaller fish by larger individu-
als is common. Grading by size is critical to prevent
cannibalism. Growth variation and cannibalism may
development. In southern flounder, optimum tempera- Marine Finfish Aquaculture 473
ture to produce the highest percentage of females is
approximately 23 °C, so water temperature should be 20.13.2.4 Grow‐out
held as close to 23 °C as possible until the fish reach System Design
75 mm in length. Flatfish are to varying degrees euryha- The unique characteristics of flatfish that must be
line, and salinity is an important consideration for man- considered by culturists during the grow‐out phase of
agement of nursery and grow‐out facilities. Euryhaline production are their preference for the tank bottom and
ability provides the culturist with flexibility in the man- their low level of activity, which affect tank design and
agement of inland hatcheries where a continuous source hydrodynamics, stocking densities, and water quality in
of seawater is not available. the microenvironment of the demersal fish. Basic
approaches to flatfish grow‐out are using land‐based
During the nursery period, turbot juveniles are fed dry tanks or raceways, or in cages deployed at sea. Many flat-
pellets (50–52% protein and 12–13% lipid) delivered fish, such as turbot, halibut, and Japanese flounder are
automatically and continuously during the photophase. cultured in outdoor land‐based tanks or in indoor tank
These diets incorporate fishmeal and fish oil as the main RAS. In general, flounder prefer low light intensities and
protein and lipid sources to avoid essential fatty acid can develop skin ulcerations when left in tanks exposed
deficiency. During the nursery stage, survival averages to direct sunlight.
over 80% and fingerlings reach 20–30 g in 6 months, with
feed conversion ratios as low as 1.0. For most flatfish spe- Along the northern coast of China, land‐based turbot
cies, culturists either use commercial diets for coldwater production tanks are held in greenhouses, preferred for
marine species (~50% crude protein, ~10–15% lipid), or their low construction cost and ease of temperature con-
manufacture diets in‐house. To reduce diet costs and trol in the winter. Concrete tanks are used. A few cage‐
improve sustainability, many researchers are focusing on culture operations exist on the southern coast of China
alternative protein sources to fishmeal. In summer floun- where the water temperature permits seasonal produc-
der, 40% soybean replacement for fishmeal reduced pro- tion. Cage culture reduces the expense of pumping water
duction cost by 14%. and facility construction and produces faster growth
rates than tank‐culture, but flatfish cages that can with-
At the end of the nursery stage, turbot are graded by stand the strong wind and currents in coastal waters are
size using machines designed for grading fruits. The needed.
most common market size for grow‐out farms is about
20 g. At this stage, turbot are often vaccinated against In Europe, turbot are grown in land‐based tanks and
vibriosis and furunculosis, but they can also be vacci- raceways usually situated in industrial buildings.
nated against diseases caused by Flexibacter and Recirculating systems are replacing flow‐through sys-
Streptococcus. Fish are transported to grow‐out farms by tems in Europe but are mechanically and biologically
ground or air transportation. In southern flounder, fin- complex and require continuous water quality control.
gerling stocking densities of about 700 fish/m2 are rec- Flat‐bottomed cages submerged in coastal areas or float-
ommended to reduce cannibalism and to promote ing cages are also used for grow‐out or to hold large tur-
growth. Cannibalism can be controlled by grading by bot prior to marketing, and sea cages are being tested in
size and frequent feeding. Fingerlings may need to be North West Spain.
graded 3–4 times during the few months it takes them to
grow from 2 g to 10 g. In Japan, land‐based tanks with flow‐through seawater
are the primary system for grow‐out of P. olivaceus, repre-
Hatchery‐reared flatfish exhibit behavioural deficien- senting 75% of production area in 2005. Approximately
cies, presumably resulting from genetic changes related 300 to 400 farms throughout Japan each produce about
to domestication and environmental experiences in cap- 16 t of fish per year. Typical land‐based flounder farms are
tivity, which make them poorly‐equipped to survive in sited seaside, with tanks either installed indoors or cov-
the wild. Compared to wild individuals, flatfish raised in ered with shade cloth. A few farms use tanks with bottoms
a hatchery tend to spend more time swimming, lack cau- covered with sand which produces fish without hypermel-
tion, have poor concealment skills, and show different anosis on the blind side to improve market value.
feeding behaviour. Hatchery fish can be provided with
substrate characteristic of the release site to allow fish to Land‐based coastal facilities are also used in Korea to
develop cryptic behavioural skills (burial and pigmen- produce P. olivaceus in flow‐through tank systems.
tation) and to reduce their vulnerability to predators. Seawater is pumped directly from the open sea into the
Other techniques, such as rearing at low density with head tanks and subsequently supplied to the fish tanks
sandy substratum, use of a diet of live mysids, and after treatment. Each farm produces an average of 110 t
predator‐exposure have been tested successfully in the per year.
laboratory.
In North America, startup commercial flatfish
p roduction facilities use RAS (see Figure 20.3) to enable
production in inland areas without a continuous source
of seawater. In Mexico, where commercial production of
474 Aquaculture Growth variation is typically observed during nursery
culture and grow‐out of flatfish, related to inter‐fish
flatfish is beginning, ambient seawater water tempera- aggression and disproportionate acquisition of food by
tures of 14–25 °C along the Baja peninsula are considered more aggressive individuals. To reduce these effects, fish
favourable to both summer flounder and California hali- are graded by hand with the aid of hand nets or mesh
but culture in both flow‐through and RAS systems, and sorters during the nursery stage and with mechanical
startup farms plan to target the large southern California graders, grading tables, or automatic machines during
market. grow‐out. Fish are separated into several size classes;
generally, twice during grow‐out.
In North America, Atlantic halibut may spend the
entire grow‐out cycle in a land‐based tank system or may Environmental Conditions
be moved to net pens for final grow‐out to market size. Optimal environmental conditions for subadult and
Although shallow tanks are considered to be more cost‐ adult flatfish are likely to be different from juveniles.
effective for flatfish production, Atlantic halibut grow For example, optimum growth temperature of Atlantic
faster in deep (1.25‐ to 3‐m deep) tanks, as shallow water halibut decreases with size from 11–14 °C at 0–20 g to
impedes access to pelleted feeds and increases inter‐fish 9–11 °C for fish of 400–1000 g. High mortality during
aggression. Atlantic halibut have also been produced in the summer affecting mainly larger size fish is well
surface cages, generally 3–7 m deep of a variety of designs known in P. olivaceus farms in Japan. In China, diseases
and materials, with a rigid base to prevent sagging when are precipitated at high temperature on turbot farms
stocked with fish. Sheltered conditions are important for and water temperature in turbot tanks is maintained
rearing flatfish in pens and cages, because currents and from 11–18 °C all year round.
waves cause excessive swimming activity. Shade netting
is used to prevent excessive exposure to sunlight which Low‐salinity tolerance is an advantage to inland‐
can cause mortality. based culture, since ground water or geothermally‐
heated water sources may be used for fish production.
Stocking and Splitting From the juvenile stages, most cultured flatfish are
Even at low stocking densities, many flatfish species euryhaline and can tolerate a wide range of salinities. In
aggregate in layers on the tank bottom rather than southern flounder, for example, growth of fingerlings
spread out across the available space, an innate behav- (~125 g) to an average market size (~600 g) in low‐salin-
iour associated with concealment in their demersal ity (0.5‰) groundwater was not different from growth
habitat for both predator avoidance and predation. in full strength seawater (36‰). Salinity tolerance may
This behavioural trait suggests that these fish could vary with age/size. For example, growth of California
potentially be raised under very high stocking densi- halibut early juveniles was unaffected at salinities rang-
ties; however, water circulation and quality deteriorate ing from 5 to 30‰, but older juveniles are not as
in and around the layers of these sedentary fish. adaptable.
Because of this behaviour, flatfish culturists often
measure stocking density in terms of percentage of Substrate has an important influence on flatfish health.
bottom coverage (PCA = percent ratio of total fish ven- Improper substrate has been associated with skin lesions
tral area to total tank bottom area), or kg/m2 rather in many species which decrease carcass quality and
than per unit volume (kg/m3) as for round fish. For growth. For example, incidence of skin lesions decreases
California halibut, better growth was achieved at 100% when Atlantic halibut, summer flounder, or P. olivaceus
PCA compared to 200 and 300% PCA. As flatfish grow are raised on a sand substrate compared to a smooth
and increase in body depth, the maximum recom- fibreglass substrate.
mended stocking density increases.
Inappropriate lighting in indoor tanks may also con-
Since flatfish do not fully use the water column as do tribute to abnormalities in hatchery‐reared flatfish.
round fish, a major challenge of intensive flatfish pro- When southern flounder raised under low light are
duction is that of maximising the use of vertical space in exposed to increased light intensity 1 week post‐hatch,
facilities that are limited in area. Raceways have been partially albino fish develop more normal pigmentation.
used for flatfish culture, and these may be stacked to The effects of illumination are complex, related to the
maximise use of vertical space. In Atlantic halibut, how- type of light used, intensity, tank colour, and water depth.
ever, raceway culture was problematic due to a reduction Excess light can be deleterious; for example, Atlantic
in water quality along the length of the raceway. halibut cultured in shallow raceways and sea cages with
Researchers have used in‐tank shelving to maximise the insufficient UV protection become sunburned. Cataracts
use of vertical space in relatively deep, conventional are common in Atlantic halibut and might be caused by
tanks. However, except for the Atlantic halibut, which excess UV light, although other environmental or nutritional
readily occupy such shelves, few flatfish species volun- factors may be involved.
tarily occupy in‐tank shelving.
Diet and nutrition Marine Finfish Aquaculture 475
Optimal levels of dietary protein for cultured flatfish
range from 45–65%, with efficient feed conversion ratios After the nursery stage, mortality of southern flounder
below 1.5 for formulated pelleted diets. The exceptional is minimal during the rest of the grow‐out cycle until the
feed conversion is probably related to naturally low fish reach market size. Survival of Japanese flounder
metabolism and a sedentary life style. In Europe, throughout the grow‐out period varies from farm to
extruded pellets formulated for turbot were developed in farm and ranges from 60 to 80%.
France during the early 1980s and are now commonly
used for commercial grow‐out. These diets have a high 20.13.2.5 Diseases
protein (50–54%) and moderate lipid content (about In general, cultured flatfish are susceptible to a host of
12%). The dietary energy content of flatfish diets is gen- pathogens commonly afflicting other intensively cul-
erally lower than that of other farmed fish species. In tured finfish, and severity and range of pathogens
Europe, high‐lipid (20%) finishing diets are used for tur- increase with the level of intensification and production.
bot when specific markets demand a higher flesh fat An increasing number of viral infections have been
content. reported in a variety of flatfish, including turbot, P. oliva
ceus and Atlantic halibut. Viral infections, usually severe
In China, disease and pollution have caused the turbot in young fish, are often asymptomatic in older fish which
farming industry to transition from raw minced fish to transmit the virus vertically to offspring and horizontally
moist pellets to commercial feeds. Currently, imported to cohorts. Since no drugs or commercial vaccines are
commercial dry pellets are formulated specifically for available to treat viral infections, control depends on
turbot, and research institutes and companies are devel- biosecurity, but this is difficult with flatfish since cultur-
oping high‐quality feeds for turbot and other flatfish in ists still depend on wild‐caught fish with an unknown
China. In Japan and in Korea, P. olivaceus are fed com- history of virus exposure.
mercial pelleted diets that have high protein (48–56%)
and low lipid (6–14%) for the first few months, and then Bacterial diseases are precipitated by stress from over-
are fed moist pellets and raw fish, either whole or as crowding, low dissolved oxygen, high ammonia, trans-
ingredients for the moist pellets. port, or high temperature. Disease prevention and
treatment protocols differ from farm to farm but with a
In Japan and Korea, studies have indicated that a signifi- common theme of limiting the use of antibiotics.
cant proportion of fishmeal protein can be replaced by sev-
eral plant and animal protein sources (e.g., soybean meal, In the US, external parasites such as Argulus spp. (sea
feather meal, meat and bone meal, corn gluten meal, malt lice) are common in wild broodstock and have caused
protein flour, fermented fisheries by‐products and soybean severe anaemia and haemorrhagic skin lesions in captive
curd residue mixture) in the diet of P. olivaceus. summer and southern flounder. Marine Ich Cryptocaryon
Combinations of multiple ingredients and inclusion of irritans is a ciliate that can cause skin and gill damage
feeding stimulants are most effective in reducing dietary and also kill a large number of fish rapidly but can be
fishmeal protein without amino acid supplements. In North treated in the euryhaline southern flounder by lowering
America, work with Atlantic halibut and southern and the salinity of the water below 3‰. Marine Ich has also
summer flounder have also demonstrated that a significant been reported in cultured Japanese flounder and turbot.
fraction (approximately 40%) of the fishmeal protein can be Turbot are highly susceptible to parasites Trichodina and
replaced with soybean meal protein (Alam et al., 2011). Uronema, and formalin baths once a month are used to
control infection.
Growth and survival
Growth rates documented for most species of flatfish are 20.13.3 Harvesting, Processing,
moderate, vary considerably among species, are highly and Marketing
variable from site to site, and are dependent on tempera-
ture. Turbot grow quickly in comparison with other spe- In Europe, asphyxia in air or on ice are not appropriate
cies of flatfish. In Europe, turbot farms using heated or for euthanasia of farmed turbot according to animal wel-
geothermal water to maintain temperatures between fare protocols, so harvested turbot are chilled rapidly
14–19 °C routinely raise turbot to 1 kg at 18 months and and then bled, but electrocution or a percussive blow to
3 kg at 3 yr. In China, turbot juveniles about 10 g can the head are also practised. Fish are transported on ice to
grow to market size of 500 g in 7–9 months in green- processing units and are usually marketed whole and
house systems. In Japan, P. olivaceus fingerlings (1–3 g) fresh, but a market for fillets is developing in Europe, and
grow to 0.5 kg in 9–10 months and 1 kg in 14–16 months. a market for live turbot is developing in Asia and in
From the egg stage, mixed‐sex populations of southern Europe. Private companies pre‐condition and package
flounder reached 600 g in 16 months. live turbot for survival up to 2 days without water to
provide maximum freshness while reducing shipping
costs. Demand is higher than supply, so there is minimal
476 Aquaculture that summer flounder culture will thrive in colder water
conditions in their country, whereas other species, such
competition between farmed and wild turbot, which are as southern flounder, will do better in warmer water
larger and command a higher market price. In France, conditions.
quality labels (e.g. ‘turbot label rouge’) certify high qual-
ity and traceability. Production efficiency of turbot farming in China can
be improved by decreasing the price of juveniles, auto-
The majority of the turbot farmed in China are mar- mation to lower labour and feed costs, better disease
keted as live fish for domestic consumption in large met- management, and improving genetics and marketing.
ropolitan areas near the east coast of China, but this Availability of saline well water, pollution of the coastal
exotic species is becoming popular throughout the coun- environment, and product safety have emerged as con-
try. Turbot are harvested between 500 to 750 g and straints to industry growth, and the application of closed
packed in polyethylene bags containing seawater and recirculation aquaculture systems will be important for
oxygen. Water temperature is maintained between the industry to expand along the northern Chinese coast.
7–8 °C during live transport to market, either by truck or
airline. Aquaculture of P. olivaceus began in the mid‐1970s in
Japan, and commercial production increased dramati-
In North America, Atlantic halibut are bled immedi- cally in the 1980s from 648 t in 1983 to a peak of 8583 t in
ately post‐mortem by incision of a major artery during 1997, a level that exceeded the annual commercial fish-
gutting or removal of gill arches, as the presence of blood ery catch in Japan. However, production gradually
veins in the fillet detracts from appearance and taste. decreased to 2600 t by 2014 due in part to competition
The fillet yield of halibut is typically around 55%. The from flounder imports from Korea. In Japan, P. olivaceus
traditional market for wild halibut is based on large fish maintains a high market price—2 to 3 times higher than
(5 to 10 kg) sold fresh and in the form of steaks. However, for yellowtail or red sea bream.
with the availability of farmed product, fish as small as
750 g are being sold to restaurants at higher prices. Start‐ Aquaculture production of P. olivaceus in Korea
up farms are targeting high‐value niche markets, includ- increased from the 1037 t in 1990 to a peak of 54 674 t in
ing sushi chefs, with live transport to optimise quality. 2009—an increase attributable in part to government
policies favouring production of high‐value species. In
20.13.4 Industry Status and Challenges 2014, production of P. olivaceus declined to 42 133 t.
Most farmed P. olivaceus are consumed in Korea, with
In Europe, turbot was selected for aquaculture in the some exported to Japan, USA, and Taiwan.
early 1970s in the United Kingdom and France due to its
value and its high potential growth rate under intensive In Japan, labour costs account for almost 20% of total
culture conditions. Global turbot production increased fingerling production costs for P. olivaceus, and labour‐
from 656 t in 1990 to 71 851 t in 2014, with China (84%) saving methods are needed to improve production effi-
the main producer, followed by Spain (11%), Portugal ciency. Diseases are a serious problem on P. olivaceus
(5%), France (0.4%) and the Netherlands (0.3%). The pri- farms, and the selection of disease‐free spawners is
mary European market is Spain, with much smaller mar- needed to avoid transmission from broodstock to larvae
kets in France, Italy, and Germany. There is market and juveniles. In Korea, where P. olivaceus farming has
demand for whole fish, and fillet markets are developing. intensified, there are growing concerns about pollution
Development of the turbot aquaculture industry in
Europe is limited by the high price of juveniles, mainly of public waters related to the discharge of effluent from
due to relatively low larval survival, and to limited access flounder farms into the sea. To reduce nutrient dis-
to seawater and conflicts with tourism. charge, diet development and improved methods for
effluent treatment are needed.
Turbot was also introduced into China from the United
Kingdom in 1992, with commercial‐scale juvenile pro- A summer flounder industry began in the USA in 1995
duction by 1999 in the Shandong province along the with the development of a commercial hatchery in New
northern coast, where the first grow‐out systems were
built in greenhouses using deep saline well water. Fish Hampshire and several grow‐out facilities, but little prod-
were initially marketed live in large cities along the uct was produced. Juveniles were first exported in 2003 to
southeast coast and within 10 yrs, developed into one of China, which now has a growing summer flounder indus-
the main mariculture industries in China, with yearly
production of over 60 000 t. China produced about try, and subsequently in 2006 to Mexico, which is also
76 000 t of flatfish (six species) in 2005 of which 50 000 t developing an industry. A hatchery for Califonia halibut
were turbot. In 2003, summer flounder juveniles were was constructed in Ensenada, Mexico, a joint effort
shipped from the USA to China, which now has a grow- between a government research and education centre
ing summer flounder industry. Chinese scientists expect
and local commercial interests, to produce juveniles to
support farms to supply the southern California market.
Pilot‐scale Atlantic halibut farming efforts are under-
way in North and South America, including a site in
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