and create additional problems related to security, navi- Salmonids 377
gational hazards, predators and servicing. Submersible
netting cages proposed for offshore sites also pose marked differences in visibility, salinity, water tempera-
another challenge in providing fish access to air to facili- ture and oxygen concentration with depth. Stratification
tate swim bladder and buoyancy regulation (Korsoen influences the depth distribution of fish within nets and
et al., 2012). There has been interest in the growth can result in high risk environments.
benefits afforded by faster swimming speeds (exercise)
in high current sites and how this may be artificially Socio‐economic factors also are important considera-
generated (Herbert et al., 2011). tions in site selection. Many sites are located in regions
remote from large urban populations with such opera-
Site selection is important in the provision of the tions providing significant social and economic benefits
correct environmental conditions for the fish, struc- to rural communities through employment, and com-
tural tolerances of the sea cage and moorings and public munity support and service programs. Important site
acceptance. Sites may be used for different purposes in features that affect the efficiency and economic viability
coastal areas. For example, specific age classes may be of the operation include access to the site to deliver
sited to match the requirements of the fish (e.g., nursery equipment, fingerlings or smolt and to remove harvested
sites for smolts) or to minimise the impacts of algal product; availability of suitable workers and their
blooms, predator attack and the spread of disease accommodation; availability of utilities; proximity of
between established grow‐out fish and newly introduced processing facilities, airports and ports; and availability
smolts. of servicing and maintenance facilities. Although these
factors are related to the site requirements for the marine
Site characteristics therefore govern the layout of the farming phase of salmonid culture, they include a
farm, cage size, net depth and management strategies number of the features for site selection that are dis-
used. For example, current speed, water exchange, site cussed in section 3.2.
depth and tidal range may determine the mooring con-
figuration, cage linkage format and net configuration. 17.4.2 Transfer to Sea Farm from Freshwater
These, in turn, determine basic management strategies Smolts or fingerlings are transferred to the seawater
(such as cage servicing from boats or directly from facilities from freshwater at a particular size and at suit-
shore), fish density, type of feeding system and net‐ able times of the year. Smolting species or strains are
cleaning regime. transferred during their ‘smoltification window’, which is
naturally in spring for Atlantic salmon, but variable for
Water temperature is of particular importance in Pacific salmon species. In Tasmania, Atlantic salmon
Tasmania. Sites experience sea temperatures of 8°C to smolt are transferred at 80–150 g (out‐of‐season S½ and
more than 23°C, promoting high growth rates during spring S1) or ~200 g (out‐of‐season S1½). The timing
some seasons but in summer there are conditions at the and length of the ‘smolt window’ vary slightly from year
limits of thermal tolerance. Warm summers and concern to year in relation to environmental conditions such as
about temperature increases associated with climate temperature. During warmer temperatures the duration
change have made this one of the major topics in the of the smolt window tends to be shorter.
industry. This is particularly related to the impacts on:
In the non‐smolting salmonids (e.g., many rainbow
●● prevalence of AGD; trout stocks), the success of transfer is size‐related:
●● fish maturation; larger fish are more adaptable to higher salinities and,
●● food intake and growth; as such, yearling fish of about 300 g are transferred in
●● feed formulations; autumn. Some farmers do not culture rainbow trout in
●● flesh pigmentation; and waters of full seawater salinity, preferring more brackish
●● market acceptance. conditions.
On some leases in Tasmania high summer temperatures In most cases smolts are transferred directly to seawa-
(and associated low DO) reduce appetite, resulting in ter from freshwater, although acclimation regimes or
loss of flesh pigmentation and slow growth (or even slightly brackish water sites are used when salmon pre‐
weigh loss). smolt or large trout fingerlings are transferred. Inclusion
of NaCl (5–10%) in the diet of smolting and non‐smolt-
Water current characteristics vary with tidal flows, ing fish a few weeks before transfer has been used to aid
which in turn influences dissolved oxygen availability. osmoregulatory conditioning.
Some sites experience low current flows while high‐
energy sites may experience current speeds up to 1 m/ A variety of methods are used to assess the timing for
sec (about 2 knots), influencing fish orientation in the transfer. Although fish may display various smolt‐like
cage, growth and even body shape. Water in some sites characteristics, the best indicator is the 24‐hr (up to 72‐hr)
(Macquarie Harbour, for example) may stratify and show 35‰ salinity‐adaptability test, which assesses the ability
378 Aquaculture or weighed during the loading process, with grading
taking place sometime beforehand. To avoid additional
of the fish to osmoregulate successfully after direct handling, the fish are not usually recounted upon arrival
transfer from freshwater to seawater. This approach uses at the sea farm. Average sizes and size range are also
osmolality or sodium measurements in blood, plasma or important because feed size and net mesh size need to
serum and the 24‐ or 72‐hr readings compared with be selected based on size of a particular batch of fish.
baseline data of fish in freshwater (usually ~280–310 In Tasmania the average size of out‐of‐season and spring
mOsm/kg). Smolt are able to regulate ionic concentra- smolts is about 100–150 g.
tions to levels close to baseline but fish not ready for
transfer may show elevated blood concentrations (e.g., 17.4.3 Sea Cage Systems
~380–500 mOsm/kg). Most sea cage are similar in basic structure: a mesh net is
suspended inside a floating collar, which is moored to the
Fish are moved to sea sites in transport tanks on sea floor (Figure 3.6). There are many sea cage shapes,
trucks where they are released via pipes into sea cages construction materials, linkage configurations and sizes.
that were towed inshore. Alternatively, fish can be taken Their form determines management strategies and servic-
to offshore sea cages in barges or boats, or can be airlifted ing practices. Some facilities use moorings that separate
by helicopter. Considerations during transport include individual sea cage to optimise water flow through and
fish density, oxygen concentration and distribution in around nets. Where water currents are not of concern,
tanks, tank ventilation, carbon dioxide de‐gassing capa- sea cages may be positioned in platforms with service
bility, total ammonia concentration and temperature walkways between pens. Some are moored offshore using
differences between freshwater and seawater at the time vessels to access the facility whereas some facilities extend
of release. from the shore with direct access by personnel and vehi-
cles. Individual sea cage sizes vary enormously from small
Transport tank densities up to ~90 kg/m3 are supported 20‐t units to large units that may hold more than 500 t.
by the use of oxygen diffused into the water, the concen- Advances in sea cage technology allow use of larger sea
tration being monitored by in‐tank probes in combination cage or sea cage systems, moored further offshore and
with displays and alarms in the truck cabin. The water possessing a number of features that enable the sea cages
may be de‐gassed to remove carbon dioxide using pumps to withstand offshore conditions, e.g., flexibility, semi‐
and spray‐bars, aeration and tank ventilation. Trips to submersible (Figure 17.10).
seafarms in Tasmania typically take 3–6 hr, which is a
relatively short transfer period.
Fish are normally deprived of food for a few days before
transport to reduce oxygen demand and excretion of car-
bon dioxide, ammonia and faecal solids. Fish are counted
Figure 17.10 Sea cages holding Atlantic salmon (Salmo salar) in Velfjorden, Brønnøy, Norway. Source: Thomas Bjørkan 2010. Reproduced
under the terms of the Creative Commons Attribution Share Alike license, CC-BY-SA 3.0, via Wikimedia Commons.
Solid bag nets were once used but have been Salmonids 379
discontinued.
biofouling is usually most dense on the net immediately
Net bags are generally 5–30 m in depth, the shape below the surface of the water extending down 2–3 m, or
being maintained by metal rings, weights (50–200 kg more depending on water clarity. Biofouling may be almost
each), lead‐core ropes or positive displacement of water non‐existent at sites with poor water clarity (waters high in
(in the case of solid bag net systems). Maintaining the tannins, for example) or widely fluctuating salinity.
shape of open mesh nets is particularly important in pre-
venting ‘bagging’ or loss of shape and volume, which Net‐cleaning practices depend on the site characteris-
occurs through the resistance of biofouled nets against tics, net material and the size of the net. Brass nets used
water currents. Net meshes on sea cages range in size to reduce predation by seals and provide some anti‐
from about 10 mm to 40 mm (bar length), dependent fouling properties (copper) have been tried but did not
upon fish size. They are generally constructed of a woven, afford much resistance to fouling. Rigid materials (rigid
knotless (raschel) synthetic material such as nylon or plastic and metal nets) and large nets are cleaned in place
polyethylene (treated for resistance against UV light), while flexible mesh (nylon and polyethylene) and small
but some farms have tested steel or brass nets (with cor- nets may be replaced by a clean net and removed from
rosion‐protecting anodes) to overcome predator attack the sea cage for cleaning. Cleaning machines utilising
and biofouling. Due to the high costs and ineffectiveness high pressure water and rotating brushes are lowered
in inhibiting biofouling, the metal nets have more vertically down the face of the net to clean the mesh in
recently been replaced by rigid plastic mesh. In Tasmania, place. Nets usually require cleaning more frequently in
nets are stocked with fish to density of about 5–15 kg/m3, summer than in winter.
producing an overall biomass at harvest of 50–500 t/cage,
depending on sea cage design, size and location. 17.4.5 Predation
The type and number of predators on seafarms vary
17.4.4 Biofouling and Net Changing considerably and are site‐specific. In Tasmania, Australian
Biofouling on nets and ropes of sea cages creates problems Arctocephalus pusillus and New Zealand A. forsteri fur
such as increased drag, increased weight, reduced water seals (Figure 17.12) can be a major threat, removing or
flow (exchange), reduced dissolved oxygen availability damaging fish through the nets or creating holes in the
and increased oxygen demand. Bacteria, protists and dia- mesh, which allow stock to escape. Many farms have
toms are early colonisers, followed by macroscopic algae, used physical deterrents such as anti‐predator nets of
hydrozoans (Figure 17.11) and other invertebrates such 10–15 cm bar mesh around individual sea cages or entire
as amphipods (e.g., caprellids). Seaweed and hydrozoan facilities. Others use traps (the seals are relocated), elec-
tronic acoustic deterrents, seal ‘crackers,’ electric fences
or high‐netted fences on each sea cage (Figure 17.13), or
Figure 17.11 Hydrozoan biofouling
growing on a sea cage net. Source:
Reproduced with permission from John
Purser, 2017.
380 Aquaculture
Figure 17.12 Seal resting on the ring float
of an Atlantic salmon sea cage. Source:
Reproduced with permission from John
Purser, 2017.
Figure 17.13 Sea cages equipped with seal and bird protective nets. Source: Reproduced with permission from John Purser, 2017.
steel/brass nets. Double nets reduce water flows and can Salmonids 381
be labour intensive and awkward to handle, so some
farmers use stiffened heavy‐ply or rigid plastic fish nets and the fish encouraged to swim between sea cages as
that are weighted taut to prevent seals from entering the nets are raised.
the nets. Seals that are relocated to other regions after
trapping will sometimes return to the farms within a few Although hand‐operated dip nets may be used on
days, and can be trapped and relocated repeatedly. Seals small farms to move fish, they are impractical on larger
have also developed behavioural strategies to overcome operations or when transferring large numbers of fish.
the deterrents. For example, they may swim with their Instead, large canvas‐lined brail nets, which are lifted
heads above the water to avoid the acoustic deterrents, by cranes, fish pumps or moving devices are used to
jump over handrails to enter the sea cages, gain entry to move fish during grading, harvesting or freshwater
the space between the predator‐exclusion barrier and bathing for AGD.
fish nets or establish territories on sea cage walkways
and sometimes attack workers and divers. Pressure‐vacuum, venturi‐driven or air‐lift pumps
are the most commonly used methods for fish pump-
Even when deterrents are successful in preventing ing; in most cases they are capable of handling fish up
losses of fish, the mere presence of seals may reduce feed to ~5 kg and have a pumping rate of about 20–30 t/hr.
intake and subsequent fish growth. However on some Problems encountered with eye, skin and scale damage
farms where seals cannot gain access to the nets, they can be reduced by system automation, operator experi-
may be seen basking on sea cages and swimming around ence or new designs that do not contain closing valves
the nets removing dead fish through the base of the net in contact with the fish. Many growers also favour
without any apparent effect on the salmon. continuous‐flow pumps over ones on a stop‐start cycle;
in some cases, 2–3 intermittent‐flow pumps may be
Seal nets around individual sea cages also help exclude connected by a manifold to create continuous flows.
diving birds, such as cormorants, which may attack fish One innovative farmer designed and built a fish moving
through the nets. Bird nets are used over sea cages— device based on corral and fish lifting systems; the
particularly smolt pens—to prevent bird attack. Gulls system being capable of rapidly moving grow‐out fish
are always present around farms, scavenging dead fish or of any size at a rate of up to 80 t/hr.
eating feed. Droppings from birds may transfer parasites
and diseases; however, this is area‐specific. Droppings 17.5 Feeds
also cause work surfaces to become slippery—a potential
work health and safety issue. 17.5.1 Characteristics
Feed costs constitute about 40–50% of production costs,
Some farms are troubled by scavengers, such as dog- so much attention has been paid to feed composition,
fish, sharks and eels, which are attracted to dead fish in feed distribution, feeding behaviour, waste levels and
the bottom of nets and their activities may damage feed ingestion. ‘Moist’ and ‘wet’ feeds (such as ground
nets and allow fish escape. Poaching and vandalism trash fish) were used during the early years of salmonid
appear to be universal problems, being addressed by sea farming. With the development of formulated ‘dry’
growers through the use of dogs, night patrols, radar or diets (pelleted feeds), problems of water quality deteri-
electronic surveillance techniques. Perceived problems oration, nutritional deficiencies and feed distribution
from dolphins and large whales do not appear to be a associated with trash‐fish diets were resolved. Further
justified risk, although their short‐term presence, like refinement of dry diets (through the extrusion process)
seals, can stress the fish, in turn reducing food intake has provided significant benefits over steam‐pressed
and growth. pellets in terms of dust content, pellet integrity, uni-
formity of size, lipid content, digestibility, buoyancy and
17.4.6 Fish Transfer on and between Sea Farms sinking rate.
Some companies use fishing boats to tow sea cages Much of the research by commercial feed companies
between lease‐sites for grow‐out and for harvesting. This concentrates on the nutritional content of the pellet,
procedure is slow, the speed dependent upon the swim- particularly the level of lipid and protein, and its digesti-
ming ability of the fish, currents, tides and bagging of the bility. Diets early in the industry contained high protein
net. Relocating fish after transfer into well boats is much levels, mostly derived from fishmeal, and low lipid levels
quicker although it does entail more handling. In other while later diets moved to a higher oil inclusion rates.
situations, fish are transferred from small to larger sea The composition of salmon diets has been developed to
cages during grow‐out and from one sea cage to another support fish at different phases and sizes in the life cycle
because of structural damage or when splitting batches (hatchery, smolt, grow‐out), exposure to different water
of fish. In these ‘swim‐throughs’ the nets are connected, temperatures and potential stress events (e.g., seawater,
382 Aquaculture down to 40 mg/kg for fish larger than 3 kg. This produces
flesh pigmentation levels of 7–10 mg/kg for Atlantic
transfer, high summer temperatures) and to build the salmon and 18–24 mg/kg for rainbow trout. Although
immune system. Typical diets may contain 38–50% laboratory‐based techniques may be used to quantify
protein, 15–35% lipid and 8–13% carbohydrate. Trout flesh pigment levels, they are usually assessed visually
diets tend to have lower energy content than salmon by comparison with standardised colour cards under
diets. Current areas of nutrition research include digest- specific lighting conditions. Pigment deposition is
ibility of carbohydrates; optimisation of lipid level; affected by fish size with small fish having lower capacity,
replacement of fishmeal and fish oils with plant proteins whereas there is loss of pigment due to redistribution to
and oils and animal meals; fish health, performance and egg development during maturation.
welfare associated with fish oil and meal replacement;
and the formulation of diets more suited to salmon Although antibiotic use has been reduced drastically
grown in warmer waters. Feed conversion efficiencies in many countries in recent years, they are used when
achieved during production have steadily improved with required to maintain animal welfare. The drugs are
advances in diet formulation and feeding practices. incorporated into the pellets during manufacture or
Typical FCRs are 0.8–0.9 for initial smolt growth and added later using oil or gelatine‐based coating. Fish from
1.2–1.4 for overall grow‐out in seawater. many Tasmanian seafarms are antibiotic free, using
husbandry techniques and vaccines to prevent or minimise
Feed pellet diameters range from 300 µm to 11 mm, the impact of bacterial diseases.
corresponding to increasing fish size from first feed to
grow‐out (and broodstock). Feeding rates depend on 17.5.2 Feed Distribution
fish stock, water temperature, location, feeding strategy, Farms use various feeding strategies (satiation, restricted,
usable energy content and feed type, but they typically maintenance and compensatory feeding) and feeding
range from ~7% body weight/d for 1 g fry to about ~1% frequencies. Generally, smaller fish require more meals
body weight/d for grow‐out (3–4 kg) fish. per day than larger fish, with particular attention paid to
the initial feeding of newly‐transferred smolt. Feeding
The orange‐pink colouration of wild salmon flesh is response can be influenced by the transfer process,
important to consumers and is produced in farmed fish smolt readiness, density and ability of smolt to begin
by inclusion of astaxanthin and canthaxanthin in the shoaling activity (Pinkiewicz et al., 2011). Pelleted feeds
feed. These carotenoid pigments, essential nutrients to are distributed mechanically or by hand. Hand feeding,
growing fish and broodstock, cannot be produced by the with the assistance of water cannons (Figure 17.14) or
fish and are normally available to wild salmon when they air‐blowers, enables personnel to assess the feeding
feed on crustaceans. Inclusion levels are determined by
companies within regulatory guidelines but are incorpo-
rated into the diet over many months. By way of example,
astaxanthin is included in transfer diets at 60–75 mg/kg
Figure 17.14 Water cannon distributing
feed pellets to smolt in sea cages. Source:
Reproduced with permission from John
Purser, 2017.
response of the fish and other aspects of husbandry, Salmonids 383
such as the presence of dead or diseased fish, general
behaviour and net damage. Hand feeding is, however, Figure 17.15 Rotating distributors for the centralised feeding
labour intensive, which limits the number of meals per system that distributed feed pellets using compressed air from
day or simultaneous distribution of meals to all sea the feed hoppers to sea cages via polyethylene pipes. Source:
cages. Fish are usually fed one to four times per day on a Reproduced with permission from John Purser, 2017.
rotational basis using this method, although smolt may
be fed more frequently. 17.6 Grading and Stocking Densities
Several types of mechanical feeders are used. They 17.6.1 Grading
may consist of storage hoppers (holding from 50 kg to 6 t) Grading is conducted in freshwater and marine facilities,
with feed distributed by spinning discs, vibrating plates, and is needed for stages from fry (section 17.3.6) to
demand feeder pendulums or augers. Pre‐programmed maturity. Grading reduces size variation in batches of
timers or computerised controls usually activate the fish or separates maturing from non‐maturing fish. Low
feeders. Many of these systems operate intermittently size variability also aids other management tasks such as
throughout the day, regardless of fish appetite. Some food pellet size and net mesh size selection and may
farms combine hand feeding with mechanical feeders so reduce the incidence of social and feeding hierarchies.
that the advantages of both are used: observation by staff
of feeding behaviour and numerous simultaneous feeds Usually, the decision to grade fish is made after the
throughout the day. size variability of a sample of fish is determined or at a
particular time of the year when maturing fish can be
Inherent in all of these methods is the potential to identified. Mechanical graders, in conjunction with fish
overfeed or underfeed, both of which can seriously affect pumps are used during size grading, whereas hand grad-
profitability. Technologies have, however, been devel- ing combined with visual assessment is used to separate
oped to address these problems, including adaptive/ the maturing grilse or jacks from the immature fish. It is
demand feeding systems, acoustic detection systems, widely accepted that these mechanical operations inhibit
air‐lift and underwater camera systems. These are used fish growth for days or weeks and some farmers either
to optimise feed distribution to the fish by monitoring avoid grading, combine it with another handling opera-
pellet wastage, fish distribution in the water column or tion or use swim‐through bar graders to separate size
consumption of pellets. groups.
More specifically, adaptive feeders are self‐regulating
and record the amount and time of feed delivery through
the use of computerised controls. They also are being
used to determine, in more detail, the diurnal and sea-
sonal feeding cycles of the fish and feeding patterns in
relation to changes in environmental conditions and
presence of predators. Improved understanding of how
feeding behaviour is affected by life stage and environ-
mental conditions can be used to refine automatic feeder
and hand‐feeding delivery strategies.
Centralised feeding systems have been used to combine
a number of positive attributes, such as operator control,
visualisation of fish activity, and pellet selection. In these
systems pellets are air blown through polyethylene pipes
(Figure 17.15) from land‐based or barge‐based feed‐
storage hoppers to sea cages. Pellet sizes and delivery
rate can be controlled by an operator in response to fish
feeding response and waste pellets viewed on monitors
(Figure 17.16) via surface and underwater cameras.
Feeding times for individual sea cages can be scheduled
in relation to tidal currents and delivery rates can be
manipulated relative to the response of the fish; as waste
pellets are detected visually the feed rates are reduced.
All of these approaches aim to minimise feed wastage
and optimise feed conversion, thereby reducing costs
and the impact of the farm on the environment.
384 Aquaculture
Figure 17.16 Control room where operators monitor fish behaviour to control the delivery rate of feed pellets to the fish and avoid
wasting feed. Source: Reproduced with permission from John Purser, 2017.
As the task of weight and length sampling can reduce to 5–25 kg/m3. The advantages of lower‐density culture
growth and add to the risk of stress and damage, tech- include improved access to feed pellets and utilisation of
niques have been developed for measuring fish in their food leading to improved growth, improved animal
sea cages without having to handle the fish. This equip- welfare, improved environmental conditions inside the
ment uses the processes of acoustics (incorporating a net, lower incidence of disease and lower concentrations
measurement of the swim bladder), stereo‐camera of waste production and improved survival.
imaging or infra‐red fish imaging to construct size‐
frequency histograms using computer technology. The Initial stocking of smolt into sea cages is much lower,
technology can be used frequently with little effect on at ~0.5–1 kg/m3, although very low densities can be
the fish and is useful for large sea cage systems; however, detrimental as these cause reduced feeding responses
the equipment must be positioned and calibrated correctly leading to poor growth and pin heading.
to be accurate.
17.7 Maturation, Sex Reversal
17.6.2 Stocking Densities and Triploidy
Stocking densities are governed by the species of salmo-
nid reared (e.g., Arctic charr can tolerate much higher 17.7.1 Maturation
densities than other species), site characteristics and Atlantic salmon begin to mature during seawater grow‐
environmental conditions. Fish in sea cages may crowd out from spring/summer and develop gonads ready for
certain zones when environmental conditions are not spawning in autumn/winter. Energy from tissue reserves
uniform, as may happen during periods of water‐column and from food intake is directed towards gonad produc-
stratification. Fish densities can increase up to 20 times tion to the detriment of somatic or flesh growth. Survival
normal densities within the preferred zones (Oppedal of maturing fish in seawater becomes increasingly
et al., 2011). Localized crowding can then impact water more difficult approaching spawning and many fish
quality, particularly dissolved oxygen concentrations. die. In addition, fish develop undesirable characteristics
that reduce their marketability, such as hooked jaws
The trend in recent years appears to favour lower den- (kype) in males, milt and egg development, change of
sities in sea cages with a reduction from ~30–40 kg/m3
body shape and condition, darkening of the skin, loss of Salmonids 385
silver appearance, loss of flesh carotenoid colour and
softening of flesh. The harvest period, therefore, is by maturing fish. The declining quality of maturing fish
determined by growth to an adequate market size prior dictates the completion of harvests of diploid fish by
to onset of maturation. early autumn, in some cases leaving a shortage in the
supply of market fish until smolt of the previous year
Age at maturity varies between species and stocks. reach a suitable size in mid‐winter. The gap in diploid
Fish may mature after one sea‐winter in regions where supplies is partially filled by triploids. Triploidy rates of
higher water temperatures promote faster growth. This 95–100% are currently being achieved in hatcheries,
is referred to as ‘grilsing’ in Atlantic salmon. Strategies to with all‐female stock being used to avoid pseudo‐matu-
deal with grilsing vary between countries. Where there is ration characters seen in triploid males. Triploidy has
a significant proportion of maturing fish, these fish may declined in popularity in many countries, but it is still
be graded from the sea cages and sold before quality used in some industries. Improved culture strategies,
deteriorates. In other areas, such as Australia, fast growth such as use of out‐of‐season smolts combined with
to an average of 3–5 kg is achieved but is also associated photoperiod manipulation, have given growers some of
with almost maturation of almost all fish after one the advantages gained previously from triploidy.
sea‐winter. In this situation, all fish are harvested. At the
other extreme, almost no grilsing occurs in colder 17.7.2 Sex Reversal
regions of the northern hemisphere and the fish remain Sex reversal of fish is discussed in detail in section 7.8.3.
on the farms for up to 3 yr. In salmonid culture, the production of all‐female stock is
a technique to avoid male fish that potentially mature
Restricted feeding at specific times of the year and earlier. It is a multistep procedure that initially produces
photo manipulation using underwater lights are two all‐male fish through the addition of 17α‐methyltestos-
strategies to delay maturation. Restricted feeding in terone in the feed for 70 days (at 10°C) at the first‐feeding
spring may provide a physiological signal to delay the fry stage. Male fish (XY) develop normally, but the female
maturation process through its effect on growth which, fish (XX) develop to also produce sperm and are termed
in itself, may not be desirable. Underwater lights are the ‘neomales.’ These fish must be dissected at maturity
preferred solution and are positioned in sea cages to (usually after 2–3 years) to remove the testes and milt, as
provide constant light to inhibit maturation (principally the neomales do not possess sperm ducts (Figure 17.17).
in out‐of‐season fish), to potentially increase growth and The resultant XX milt is used to fertilise eggs, resulting
to recondition maturing fish. Despite the increased day in all‐female (XX) fish which are grown to market size.
length provided by artificial lighting, feed is not routinely It is essential that the hormone used in this procedure is
offered to fish during the ‘true night’ phase. not offered to market fish, only to the broodstock. It is
for this reason, and the need to use the fish for this
Production of all‐female stock and sterile triploid fish specific task, that neo‐male stock must be identifiable
(particularly all‐female) are strategies to extend availability
of market fish year‐round, overcoming limitations caused
Figure 17.17 Sex‐reversed (partial) female
showing the globular testes and ovary.
Source: Reproduced with permission from
John Purser, 2017.
386 Aquaculture have all improved fish survival and condition. Some of
the more serious diseases that have been encountered
and maintained separately during grow‐out. Neomales worldwide include:
may also be produced by bathing pre‐feeding fry in a
testosterone‐based bath, but this technique results in ●● Viral diseases:
neomales that express milt; a characteristic that may –– infectious salmonid anaemia (ISA); and
cause some confusion with ‘normal’ male fish. –– infectious pancreatic necrosis (IPN).
17.7.3 Triploidy ●● Bacterial diseases:
The triploidy‐inducing process occurs at the fertilised –– piscirikettsiosis (Piscirickettsia salmonis);
egg stage. It may be used on eggs in conjunction with sex –– bacterial kidney disease (BKD; Renibacterium
reversal techniques to produce all‐female triploids or salmoninarum);
separately to produce mixed‐sex triploids. As it induces –– vibriosis (Vibrio spp.):
sterility it can be used to overcome problems normally –– furunculosis (Aeromonas salmonicida); and
associated with maturation. –– enteric redmouth (Yersinia ruckeri).
Eggs at approximately 30 min post‐fertilisation (at ●● Protozoal and crustacean parasites:
10°C) are subjected to heat or hydrostatic pressure shock –– sea‐lice (Lepeopthierus and Caligus); and
for a specific period of time. Details are specific to indi- –– AGD; Neoparamoeba perurans).
vidual species, sizes of eggs and method of shock treat-
ment, but as an example thermal shock occurs at 28.5°C AGD has a major impact on the Tasmanian farmed
for 10 min and pressure shock at ~69 000 kPa (~10 000 salmon industry, contributing up to 20% of production
psi) for 5 min, both followed by re‐exposure to 10°C costs. Once thought to be restricted to Tasmania, it has
water. After this treatment, normal rearing conditions now been detected in 14 countries across six continents.
are used. Although sterility is a characteristic of triploid While its greatest impact is in the Atlantic salmon marine
fish, some male fish display pseudo‐maturation features. farming sector it has been found associated with 15 fish
This may be overcome by producing all‐female triploids; species (Oldham et al., 2016). The increase in production
the eggs are fertilised by sperm from neomales and then costs associated with AGD is primarily due to depressed
subjected to the triploidy process. growth, mortality and the high labour costs that are
associated with frequent bathing of the fish in freshwa-
Triploid fish sometimes suffer from deformities such ter, which is used to reduce the incidence of the disease
as shortened opercula and jaw deformities (‘drop‐jaw’). and its resultant mortalities. Freshwater bathing uses
They also may possess different physical and behavioural tarpaulin liners positioned in new sea cages and filled
characteristics (e.g., flesh characteristics and body shape) with freshwater. Fish are pumped from the sea cages
and show different tolerances to environmental condi- through a de‐watering apparatus to the freshwater bath
tions. As such, alternative strategies discussed above in the tarpaulins, where they remain for a few hours
have been developed to overcome problems associated before the tarpaulins are removed. For much larger sea
with maturation. cage systems, well boats—also used for transporting and
harvesting fish—are used to treat fish.
17.8 Fish Health
Originally experienced only in summer, AGD is now
A number of diseases occur in farmed salmonids: some prevalent throughout the year, mainly at full seawater
are widespread while some are specific to certain regions. sites rather than low salinity (or freshwater flush) locali-
Relatively isolated regions, such as Tasmania, are largely ties which have now been developed to minimise the
‘disease‐free’ in terms of the incidence of serious bacte- incidence of AGD. Bathing frequency depends on yearly
rial and viral conditions. This may in no small measure environmental conditions, but generally is 8–13 times
be due to strict quarantine laws prohibiting the importa- per sea cage per cycle (Kube et al., 2012). Alternative
tion of salmonid stock, gametes and some salmonid treatment and prevention methods involving immune‐
retail products. In general, the incidence of disease in stimulants, food additives, selective breeding and vaccines
farmed salmon is decreasing. Preventative management have been researched for AGD management.
strategies, many of which minimise fish stress, are
favoured over antibiotic treatments. The use of embay- The pathogenic bacterium Vibrio anguillarum has
ment or coastal management strategies with restricted been controlled by the development of a vaccine that is
stock movement between sites, improved diets and administered to the fish as a bath at the freshwater stage.
reduced on‐site stocking densities, together with site Outbreaks of enteric redmouth caused by Yersinia ruckeri
fallowing strategies and the development of vaccines, occur in freshwater and after transfer to seawater; these
can cause ongoing mortality. The disease is controlled
through management techniques, a vaccine and limited
antibiotic treatments.
Salmonids 387
Other health conditions occur occasionally as a con- 17.10 Environmental Issues
sequence of algal blooms, periodic influxes of jellyfish,
inflammatory reactions to the use of certain plant proteins Minimising the negative effects of aquaculture on the
in diets and nutritional problems such as those associated environment and, conversely, the negative effects of the
with vitamin deficiency and food spoilage. environment on the cultured fish are major challenges in
the salmonid industries. Prolonged use of marine sites,
17.9 Harvesting and Products accompanied by poor husbandry practices and poor
siting, may cause ‘souring’: a condition where growth and
The average size of salmonids at harvest is determined by survival decrease and disease incidence may increase. It is
market demand balanced against the cost of production. therefore in the company’s economic interest to carefully
As examples, plate‐sized freshwater trout may be har- choose sites and conscientiously manage sea cages.
vested at 200–400 g, whereas sea‐grown trout may occupy
a different market niche at 3–5 kg. Atlantic salmon may be There are some environmental issues that are common
harvested as one‐winter fish or ‘grilse,’ which may vary to sea cage farming, not only with salmonids, and some
considerably in quality and size (depending on country) other forms of aquaculture. They often lead to opposition
and range from 1.5–6 kg. Fish that are two winters or older to new aquaculture proposals.
or ‘salmon’ are usually 3 kg and above. In Tasmania, 3–4 kg
trout are produced in about 10 months in sea cages while 17.10.1 Solids Pollution
salmon are harvested at about 4 kg, or more, between
12–15 months post‐transfer. Solid wastes from uneaten food and faecal material may
accumulate on the seafloor under the sea cages. Initially
Before harvest, samples may be taken to determine this may be a source of food for fish and increase benthic
quality characteristics such as fat content, flesh coloura- invertebrate productivity, but over time, the oxygen
tion, average size, size range, shape and occurrence of demand increases, and the sediment becomes anoxic,
marks. Fish usually are food‐deprived for a few days prior causing a decline in the diversity of benthic invertebrates.
to harvest to empty the digestive tract which could con- In extreme cases, accumulation of organic matter and
taminate the flesh during gutting and processing. During anoxic conditions lead to the production of hydrogen
the harvest process, fish are crowded (but to maintain sulphide, methane and ammonia gases which may rise
minimal distress), removed from sea cages using fish through the water column as bubbles potentially influ-
pumps or brail nets, then stunned, bled and chilled in ice encing the health of the fish.
slurry, lowering the core temperature to below 3°C to pre-
serve carcass quality (Figures 13.3, 13.4 and 13.5). The ice Sea cages may periodically be moved around the lease
slurry/carbon dioxide combination once commonly used area or rotated between different leases to allow for
in industry to stun the fish produced elevated lactic acid recovery of the substrate. The time required for recovery
and lowered pH levels in the flesh, leading to issues of ranges from a few months for sites with good water flow
gaping and softness. Consequently, carbon dioxide has up to several years for poor sites. Several sites may be
been replaced by techniques which promote a rested used and each site may be used for specific age classes of
harvest: anaesthetic baths using AQUI‐S™ or more com- fish. This production strategy enables sites to be fallowed
monly by percussion stunning. between production cycles. Site rotation and fallowing
are strategies that can be used in conjunction with, not
Approximate product recovery rates from live instead of, sound husbandry practices to manage sites.
Atlantic salmon are 82–86% for head‐on‐gilled‐and‐ Growers are aware that available sites are limited natu-
gutted (HOGG), 60% for skin‐on fillets and 50% for rally and by government regulation and that these need
skin‐off fillets (50%). Salmonid products contain high to be used sustainably.
levels of long‐chain n‐3 fatty acids especially DHA and
EPA, and they are sold around the world as fresh fish, Independent monitoring by government authorities of
whole head‐on, head‐on‐gilled‐and‐gutted fish, fresh sediment condition under sea cages is now standard
fillets, cutlets and portions, frozen HOGG fish, hot and practice in many countries. Visual assessment using
cold smoked sides, portions or whole fish, gravlax underwater video, chemical assessment (e.g., redox
(lightly sugar cured), pâté and rillettes, caviar, heads potential) and biological assessment (benthic in‐fauna,
and ready‐made meals. Beggiatoa mats) are components of such a monitoring
program. While the impact of farming on the substrate
There is an excellent range of products from one has been a focus, growers also closely monitor water
species, Atlantic salmon, and this explains some of the quality parameters such as dissolved oxygen, tempera-
attractiveness of this species to consumers and fish ture, salinity, turbidity, current speed and direction, and
farmers. micro‐algal composition and concentration vertically
through the water column.
388 Aquaculture The equivalent value for rainbow trout was more
than 800 000 t.
17.10.2 Chemical Pollution ●● Salmonids can be cultured entirely in freshwater, as for
Chemical inputs of antifoulants, antibiotics, anaesthetics rainbow trout. However, the culture cycle typically
and disinfectants have been of concern through their involves a freshwater hatchery stage to produce finger-
effect on non‐target fauna and development of microbial lings or smolt, which are then transferred to grow‐out
resistance to antibiotics (Burridge et al., 2010). However, in the sea (Atlantic salmon and rainbow trout).
the use of chemicals has been reduced significantly as ●● The replacement of a high proportion of fishmeal and
antifoulants are replaced by stiffened nets and net‐ fish oil in the diets of cultured Atlantic salmon with
cleaning devices, antibiotics by vaccines, anaesthetics plant meals and oils has been a major development in
by percussion stunning at harvest and a strict control of sustainable production.
disinfectants. ●● Disease has a major impact on production but signifi-
cant advances in biosecurity, vaccine development
17.10.3 Genetics and Disease and prevention strategies using husbandry and site
Escapees from farms as a result of holes in the nets cre- management have reduced the use of antibiotics and
ated by predators and collision by large debris, or by other treatment measures.
accidental release not only incur a financial loss but ●● The development of rested harvests, automated per-
potentially impact native fish through genetic contami- cussion stunning machines, automated processing
nation of wild salmon populations and disease transmis- lines and packaging have optimised product quality
sion to these populations. and shelf life.
●● Atlantic salmon are characterised by its versatility in
17.11 Summary the market place with a diverse range of products
including fresh fish, hot and cold smoked fillets, pâté,
●● Salmonid species are important in aquaculture, rillettes, gravlax, caviar, and pre‐prepared meals.
world capture fisheries and recreational angling. ●● The high level of industrialization involved in sea cage
These species include Atlantic salmon, rainbow culture of salmonids, as with other large‐scale sea cage
trout, Chinook salmon, coho salmon, chum salmon, culture, has raised issues of environmental sustainability.
pink salmon, sockeye salmon, brown trout, brook There are now development plans and management
trout and Arctic charr. strategies that involve environmental monitoring,
guidelines on fish loading and nutrient input, attention
●● Atlantic salmon and rainbow trout are by far the to social license, interrogation of stakeholder values
most important. Total production of Atlantic salmon and whole of system planning.
from aquaculture was more than 2.3 million t in 2014.
References Kube P.D., Taylor R.S., and Elliott N.G. (2012). Genetic
variation in parasite resistance of Atlantic salmon to
Burridge, L., Weis, J.S., Cabello, F. et al. (2010). Chemical amoebic gill disease over multiple infections.
use in salmon aquaculture: A review of current practices Aquaculture, 364, 165–172.
and possible environmental effects. Aquaculture, 306,
7–23. Lien, M.E. (2015). Becoming Salmon: Aquaculture and the
Domestication of a Fish. University of California Press,
Coates, P. (2006). Salmon. Reaktion Books, London. Berkeley.
Haworth, J. (2010). Swimming Upstream: How Salmon
Oldham, T., Rodger, H. and Nowak, B.F. (2016).
Farming Developed in New Zealand. Wily Publications, Incidence and distribution of amoebic gill disease
Christchurch. (AGD)—an epidemiological review. Aquaculture,
Herbert, N.A., Kadri, S. and Huntingford, F.A. (2011). A 457, 35–42.
moving light stimulus elicits a sustained swimming
response in farmed Atlantic salmon, Salmo salar L. Fish Oppedal, F., Dempster, T. and Stien, L.H. (2011).
Physiology and Biochemistry, 37, 317–325. Environmental drivers of Atlantic salmon behaviour in
Korsoen, O.J., Fosseidengen, J.E., Kristiansen, T.S. et al. sea‐cages: a review. Aquaculture, 311, 1–18.
(2012). Atlantic salmon (Salmo salar L.) in a submerged
sea‐cage adapt rapidly to re‐fill their swim bladders in an Pankhurst, N., Purser, G. J., Van Der Kraak, G. et al. (1996).
underwater air‐filled dome. Aquacultural Engineering, Effect of holding temperature on ovulation, egg fertility,
51, 1–6. plasma levels of reproductive hormones and in vitro
ovarian steroidogenesis in the rainbow trout Salmonids 389
Oncorhynchus mykiss. Aquaculture, 146, 277–90.
Pennell, W. and Barton, B. A. (eds) (1996). Principles of Thoen, E., Evensen, O. and Skaar, I. (2016). Factors
Salmonid Culture. Elsevier, Amsterdam. influencing Saprolegnia spp. spore numbers in Norwegian
Pinkiewicz T.H., Purser G.J., and Williams R.N. (2011). salmon hatcheries. Journal of Fish Diseases, 39(6), 657–665.
A Computer vision system to analyse the swimming
behaviour of farmed fish in commercial aquaculture Van de Vis, H., Kiessling, A., Flik, G. et al. (Eds.) (2012).
facilities: A case study using cage‐held Atlantic Salmon. Welfare of Farmed Fish in Present and Future Production
Aquacultural Engineering, 45, 20–27. Systems, Springer, Dordrecht.
Wild‐Allen, K. and Andrewartha, J. (2016). Connectivity
between estuaries influences nutrient transport, cycling
and water quality. Marine Chemistry, 185, 12–26.
391
18
Tilapias
Victor Suresh and Ram C. Bhujel
CHAPTER MENU 18.7 Nutrition, Feeds and Feeding, 401
18.1 Introduction, 391 18.8 Grow‐Out Systems, 405
18.2 Family, Species and Genetic Variation, 393 18.9 Disease Management, 410
18.3 Ecology and Distribution, 395 18.10 Harvest, Processing and Marketing, 412
18.4 Sex Determination and Reproduction, 396 18.11 Summary, 413
18.5 Control of Reproduction, 397
18.6 Seed Production, 399 References, 414
18.1 Introduction tilapias, but most of it is exported as high‐value, fresh‐
chilled fillets to the USA. Imports of tilapia fillets into
Fish resembling tilapias were featured in paintings in the USA exceeded 190 000 t and were valued at over
the Egyptian tombs of 2500 BCE (Figure 18.1). Some USD 1 billion in 2014.
believe that it shows that tilapias were cultivated in
ancient Egypt. It is also claimed that the fish caught by The remarkable success of tilapias as a farmed fish can
Jesus’s disciples in the Sea of Galilee and fed to the mul- be attributed to three main factors:
titudes were tilapias. Such claims may be disputed 1) Desirable flesh quality. Tilapias have white flesh, with
because of the lack of hard evidence, but there is no
doubt that tilapias are one of the most successfully neutral taste and firm texture. As a result, tilapias
and widely cultured fish of modern times. Global pro- have gained acceptance in a wide variety of human
duction of tilapias in 2014 exceeded 5 million t/yr cultures with differing tastes and food preferences.
(Figure 18.2) making it the second only to the carps as 2) Ease of farming. Tilapias are easy to hold and breed in
the largest species group in production volume.1 China, captivity. They tolerate crowding, relatively poor
Indonesia, Egypt, Bangladesh and the Philippines lead water quality and are relatively resistant to infectious
global production (Table 18.1). diseases. They can be grown in a wide variety of aqua-
culture systems (Table 18.2).
Most tilapias grown in these countries through aqua- 3) They eat algae and detritus naturally produced in cul-
culture are used for local consumption, but there is also ture systems as well as manufactured feeds containing
substantial international trade of chilled and frozen tilapia ingredients derived from plants. They reach typical
products. The largest importer of tilapia is the USA, market size (500–800 g) in about 6–8 months under
where consumption of tilapia has increased more than optimum water temperature (28–30 °C).
five‐fold in the last decade. Consumption of tilapia in the Based on these characteristics and realising the poten-
USA has exceeded that of trout since 1995 and has become tial of the fish as a farmed food, tilapias have been
the most preferred finfish by consumers after tuna and called ‘aquatic chickens’ because they can be farmed as
salmon. Central American countries, particularly Costa easily and economically, and with the same broad mar-
Rica and Honduras, produce relatively small volumes of ket appeal, as chicken.
The ability of tilapias to breed prolifically in captivity
1 All production data in this chapter were obtained from the 2016 without requiring hormone injections was thought to be
FAO Fishery and Aquaculture Statistics FishStatJ database an attractive attribute as a farmed fish. However, it turned
http://www.fao.org/fishery/statistics/software/fishstatj/en out to be a critical problem in producing tilapias to
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.
392 Aquaculture
Figure 18.1 Wall painting on the tomb of Menna, Royal Estate Supervisor. Plate V La Pêche, Peintures Égyptiennes, Orbis Pictus volume
30, Payot Lausanne. Printer: Hallwag S.A. Berne.
6 Table 18.1 Global tilapia production by countries in 2014.
5 SN Country Production (t) Share (%)
Production (Million t/yr) 4 1 PR China 1 698 483 31.6
2 Indonesia 1 040 594 19.3
3 3 Egypt 14.1
4 Bangladesh 759 601
2 5 Philippines 283 937 5.3
6 Vietnam 259 198 4.8
1 7 Brazil 244 483 4.5
8 Thailand 198 728 3.7
9 Others 188 946 3.5
706 230 13.2
Total 5 380 200 100.0
0 Source: Data from FAO (2015).
1970
1980 1990 2000 2010
Figure 18.2 Global production of tilapias in aquaculture, increases competition for food and other resources,
1989–2014. Data from FAO (2015). resulting in slower growth of the originally stocked fish.
Thus, a number of solutions to this problem have been
uniform and acceptable market size (>300 g) due to their developed by researchers and tilapia farmers. Most solu-
early and uncontrolled reproduction in culture systems, tions rely on the production and stocking of all‐male
especially in earthen ponds. Their early maturation and t ilapia. Male tilapias grow faster than females and, there-
frequent reproduction directs a significant amount of fore, all‐male tilapia populations provide an added
physiological energy towards gonadal development and growth factor, besides controlling unwanted reproduc-
breeding activities, and thereby reduces the energy avail- tion and recruitment. Common methods of producing
able for growth (see Figure 8.1). Furthermore, uncon- all‐male tilapias are described in section 18.5.
trolled recruitment of offspring in the culture system
Subsequent sections of this chapter provide a more
detailed account of tilapia biology and culture. Tilapias
Tilapias 393
Table 18.2 Characteristics of tilapia grow‐out culture systems.
System type Extensive Semi‐intensive Intensive Super intensive
Small ponds, Cages, tanks,
Stocking density (no. Ditches, rice fields, backyard Ponds built specifically for tanks, cages, raceways
of animals/m2 or m3) ponds, community ponds, fish farming raceways
Source of seed reservoirs and tanks for >20
(fingerlings) for irrigation 2–5 >5 Own or
stocking ~1 commercial
Reproductive control Own or commercial Own or hatcheries
Fertilisation Wild fish, by‐product of hatcheries commercial All‐male stock
Feeds culture hatcheries None
All‐male stock may be used All‐male stock Complete,
Aeration/water None Manure and inorganic None compounded feeds
exchange None except incidental, fertilisers applied
Culture duration run‐off fertilisation Farm by‐products such as Complete, High
Yield (mt/ha/crop) None except occasional farm rice bran, oilseed cakes or compounded feeds 4–6 months
Market by‐products and household supplementary compound >20
wastes feeds Used frequently Urban, high‐value,
Limited, occasional water export markets
None exchange 4–6 months
6–9 months 5–20
Seasonal 1–5 Urban, high‐value,
~1 Local and national, export export markets
Producers’ own markets
consumption and local, rural
markets
are better understood than most aquaculture species about 10 genera and over 100 species within Tilapiini.
because they have been a focus of research for more than The common term ‘tilapias’ refers to pure species as well
50 yr. In addition, much fundamental research has been as hybrids belonging to the genera Tilapia, Sarotherodon
undertaken on tilapias because of the ease with which and Oreochromis, especially the larger species that are
they can be maintained in the laboratory and because of commercially exploited. The three major genera are dif-
their short production cycle. Much of tilapia culture ferentiated by the way they brood their eggs and larvae:
technology has resulted from understanding specific 1) Tilapias of the genus Tilapia lay their eggs on a sub-
biological characteristics of tilapias. These are summa-
rised in detail in a number of publications such as strate, which may be a depression on the pond bottom
Beveridge and McAndrew (2000), El‐Sayed (2006), Lim or tree roots or submerged vegetation. Both parents
and Webster (2006) and Bhujel (2014). care for the eggs until hatch. Females fan and clean the
eggs with their fins while males guard the territory.
18.2 Family, Species and Genetic 2) Tilapias of the genus Oreochromis lay their eggs in a pit
Variation or nest prepared and guarded by the males. After the
eggs are laid, the female parent incubates the eggs in her
18.2.1 Family mouth. Parental care continues for several days even
Tilapias belong to the family of Cichlidae, a large family after the eggs hatch and the fry are free‐swimming.
of tropical freshwater fish, which have a bilaterally com- Most farmed tilapias belong to the genus Oreochromis.
pressed body and exhibit parental care. Cichlid fish have 3) Tilapias of the genus Sarotherodon are similar to
a wide natural distribution throughout the tropics but the Oreochromis in their reproductive behaviour but both
tribe, Tilapiini, to which tilapias belong, occurred only in parents (or only the male parent) perform mouth
Africa and Palestine until translocations began. There are brooding of their eggs and fry.
Further details of reproduction in Oreochromis species
are provided in sections 18.4–18.6 in this chapter.
394 Aquaculture individuals survived and formed the basis of the Japanese
stock that exists today. About 50 individuals of this
18.2.2 Species Japanese stock were presented to the King of Thailand in
1965 and were placed in a pond at Chitralada Royal
Among the tilapias, members of the genus Oreochromis, Palace. This stock formed the basis of the Chitralada
such as O. niloticus and O. aureus, are favoured in aqua- strain, which has performed exceptionally well under
culture because of their performance under culture con- Thai farming conditions. Similarly, a number of other
ditions (Table 18.3). Among the pure species, O. niloticus strains of O. niloticus exist in Asia and elsewhere. These
(Nile tilapia) is favoured. The exceptional growth of this strains are known by their origin in Africa (such as
species in tropical freshwater conditions is the reason for Ugandan strain or Ghanaian strain) or the intermediate
its success. However, it is less cold tolerant and does not locations from which they were transferred (such as
perform well in higher salinity waters (>15‰). So, in Israeli strain or Taiwanese strain) or the destination in
subtropical waters, the more cold‐tolerant O. aureus which they were further domesticated (such as the
(blue tilapia) is the species of choice. Species such as O. Philippines strain or Chitralada strain).
spilurus, which tolerate and grow at high salinity, are
considered for farming in seawater, particularly in the 18.2.4 Hybrids
Middle East, where freshwater resources are limited.
Mozambique tilapia (O. mossambicus) was the first tila- There are several naturally occurring tilapia hybrids aris-
pia species introduced into various parts of Asia during ing from two or more species sharing a geographic loca-
1950s. It has, however, lost favour because of excessive tion. Some of these natural hybrids are good candidates
reproduction that has created a bad reputation as a fish for aquaculture. Intentional hybridisation for aquacul-
that stunts early in culture and rarely reaches its genetic ture purposes started with the accidental discovery that
potential for growth and ultimate size. It has therefore crossing female O. mossambicus with male Oreochromis
been replaced by Nile tilapia or red hybrids for commer- urolepis hornorum resulted in all‐male offspring.
cial culture. Subsequent research showed that several other crosses
also produce all‐male or predominantly male offspring
18.2.3 Strains (Table 18.4). This was attributed to the differences in sex
determination mechanisms between different tilapia
The wide geographic presence of species such as species (see section 18.4). Hybrids from female Nile tila-
O. niloticus in Africa has led to significant genetic diver- pia and male blue tilapia are widely used in China. The
gence, resulting in distinct subspecies and strains. Their cross yields high male percentage (80–90%), and results
subsequent transfers outside Africa have also provided in fast growth, large size, and tolerance to cold tempera-
opportunities for further development of distinct strains. ture, and a wide range of salinity.
For example, about 200 individuals of O. niloticus
were sent from Cairo to Japan in 1962. Out of these, 120
Table 18.3 Characteristics of Oreochromis species suitable for aquaculture.
Species Growth Critical environmental Suitability
O. niloticus Fastest growing species in tolerance factors
O. aureus many countries. Maximum Highly suitable for farming in
size 2 kg Lower lethal temperature tropical, freshwater and brackish
O. mossambicus Fast growing species. ~12 °C; does not tolerate water systems
Maximum size 2 kg high salinity Best candidate for farming in
O. spilurus Tolerates cold temperatures subtropical freshwater and
Fast growth and large relatively better than most brackish water systems
maximum size (~1.5 kg) species (lower lethal
observed in wild, but temperature ~8 °C) Suitability as a pure species is
stunting common in culture Lower lethal temperature questionable. A good candidate for
Grows fast when young but ~10 °C. Grows well and hybridisation if salinity tolerance is
slows down in adulthood. reproduces under salinities desired in the offspring generation
Maximum size ~1 kg as high as 35‰ A good candidate for mariculure.
Low tolerance to cold
temperatures like most
other Oreochromis species,
but perform extremely well
at high salinities
Tilapias 395
Table 18.4 Tilapia crosses of Oreochromis and Tilapia species that result in all‐male or predominantly male offspring.
Female Male Males in offspring generation (%)
O. mossambicus O. urolepis hornorum 100 in pure strains
O. niloticus O. urolepis hornorum 100 in pure strains
O. niloticus O. nyasalapia macrochir 100 in selected strains
O. niloticus O. variabilis 100 in pure strains
O. niloticus O. aureus 100 in selected strains and
70–80 in mass spawning
O. spilurus niger O. nyasalapia macrochir 100 in pure strains
T. zilli O. andersonii 100 in pure strains
18.2.5 Red Tilapias Tilapia (GIFT) developed by WorldFish in collaboration
One of the significant advances in tilapia farming was the with BFAR (Bureau of Fisheries and Aquatic Resources),
development of ‘red tilapias’ in the 1980s. Most tilapias, Government of the Philippines. The GIFT was developed
particularly O. mossambicus, which was then a widely by crossing four wild and four domesticated strains of
distributed species in Asia, have a dark grey‐black skin O. niloticus followed by combinations of family and mass
colour. The peritoneum of the abdominal cavity is also selections for body weight. Field trials demonstrated that
black in colour. This colouration was deemed unattrac- the first‐generation GIFT line yielded 18–58% larger fish
tive in several markets, resulting in poor consumer compared with local strains of O. niloticus.
acceptance of the fish. Mutants that possessed red skin
were observed in O. mossambicus, first in Taiwan, and GIFT tilapia lines have been transferred to many coun-
later in the USA and Israel. These mutants were devel- tries in Asia and beyond and subjected to further genetic
oped into red O. mossambicus strains (Table 18.4), which improvement through selective breeding. For example,
evoked strong commercial interest in the culture of tila- the ninth generation of GIFT strain referred to as GIFT‐
pias. Red tilapias not only lacked the stigma associated strain Super Tilapia, or GenoMar Supreme Tilapia™, was
with the colouration of the wild‐type tilapias, but also introduced into China in 2001. The GIFT line has now
resembled premium marine species such as sea bream been bred over several generations and been field‐tested
and red snapper. They had the potential to achieve wider in many countries such as Bangladesh, India, Thailand,
consumer acceptance and higher prices in many markets. and Vietnam.
As pure O. mossambicus red strains grew poorly, they
were hybridised with faster‐growing tilapias, such as Additional efforts have also been made towards genetic
O. niloticus, O. aureus or others. As a result, a large num- improvement of tilapias, including transfer of genes. At
ber of red tilapia strains are available for fish culturists. least two lines of true‐breeding transgenic tilapias have
There are differences among the hybrid strains in colour been established. One is an O. urolepis hornorum‐based
intensity, growth rate, and tolerance to low temperature hybrid that expresses a transgenic tilapias growth hor-
and tolerance to high salinity. Because many red tilapia mone gene and grows 55% faster than its non‐transgenic
strains were originally derived from O. mossambicus, counterpart. This was developed in Cuba and has been
they perform well in saline environments but may have approved for use in commercial production in that coun-
slow growth and low tolerance to cold temperatures. try. The other line is an O. niloticus that is transgenic for a
salmon growth hormone and grows 3–4 times faster than
18.2.6 Genetically Improved Tilapias its non‐transgenic counterpart. This line was developed
Despite the impressive growth rates of some strains of in the UK and is yet to be approved for commercial use.
tilapias, such as the Chitralada strain of O. niloticus, the
genetic base of tilapias in many countries used to be 18.3 Ecology and Distribution
rather poor. Genetic improvement by means of selective
breeding, crossbreeding or both has been applied in 18.3.1 Natural Habitats
developing strains of tilapias targeting a specific trait Africa, excluding Madagascar but including parts of the
(mainly growth rate). A well‐documented effort in tilapia Middle East, is the original home of all tilapias (Figure 18.3).
genetic improvement is the Genetically Improved Farmed In general, Oreochromis species are endemic to the cen-
tral and eastern parts of Africa, whereas Tilapia and
Sarotherodon species are more common in the western
396 Aquaculture
The first translocation outside Africa occurred in the
early 1930s, when O. mossambicus was introduced into
Java (part of present‐day Indonesia). From there it was
introduced into much of tropical Asia and eventually
into the Americas. Most of the introductions were
p urposeful; mainly for controlling aquatic weeds and
insect pests, for keeping as aquarium fish, farming or
enhancing fisheries. But a number of accidental and
undesirable introductions have also occurred. For
example, O. mossambicus was introduced into Australia
(Queensland) in the 1970s as an aquarium fish, which
then escaped into natural waters and became estab-
lished as a feral population. Currently, it is regarded as
a pest species that threatens the natural ecosystem it
occupies. Other tilapias that have been deliberately
introduced for farming purposes have also established
their natural populations over a wide geographic range,
include O. niloticus, O. aureus, O. urolepis hornorum,
Tilapia rendalli and T. zillii.
Figure 18.3 An African woman selling cooked tilapia at a roadside 18.4 Sex Determination and
market. Source: Reproduced with permission from Les Torrans. Reproduction
parts. However, species such as Tilapia zillii, Sarotherodon 18.4.1 Sex Determination
galilaeus and O. niloticus have a much larger native range. Sex determination in tilapias is highly complex, with
Another well‐known species, O. aureus, is native to the gender being determined by genetic, environmental and
Nile delta and the Middle East. hormonal factors. Genetic determination is primarily
through sex chromosomes and two different mecha-
Tilapias are considered to have evolved as riverine fish nisms for sex determination through sex chromosomes
that eventually colonised lakes. They can be found in a have been proposed:
wide variety of natural ecosystems, including slow‐moving ●● species such as O. mossambicus and O. niloticus pos-
parts of rivers, floodplain pools, swamps, lakes and coastal
lagoons. They are strictly a warm water species. They stop sess a system similar to humans in which females are
growing at temperatures below 16 °C and do not survive homogametic (XX) and males are heterogametic (XY);
below 10 °C. They survive and grow in brackish waters and ●● species such as O. aureus and O. urolepis hornorum
many species can tolerate, and grow in, seawater. Adult possess a system in which females are heterogametic
tilapias primarily eat plant materials (phytoplankton, ben- (WZ) and males are homogametic (ZZ).
thic algae, macrophytes, etc.) and detritus derived from A cross of the species with different systems results in all‐
plant materials. They are also highly opportunistic feeders male or predominantly male progenies as shown in
that are capable of changing their choice of food items or Table 18.5. Apparently, the male‐determining gene (Z) in
their feeding habits depending on food availability.
18.3.2 Translocations Table 18.5 Sex determination systems in tilapias that result
The ability of tilapias to adapt to a wide variety of in all‐male or predominantly male progenies.
environmental conditions has led to the successful
translocation of many tilapias within and outside Africa. O. mossambicus, female (XX) × O. urolepis hornorum, male (ZZ)
↓
XZ (all‐male hybrid)
O. urolepis hornorum, female (WZ) × O. mossambicus, male (XY)
↓
WX (25% female hybrids)
WY, XZ, YZ (75% male hybrids)
the WZ system dominates the female‐determining gene Lek (Spawning arena) Tilapias 397
(X) in the XY system, whereas the male‐determining
gene (Y) in the latter dominates the female‐determining Ovulation & Oral incubation
gene (W) in the former. Spawning (<2 hrs) (5–10 days)
A number of studies have shown that sex chromo- Nest building & Nursery (10–30 days)
somes are not alone in determining sex in tilapias. Genes Courtship (1–5 days)
in autosomes are suspected of playing a role in determin-
ing sex in O. niloticus and O. aureus. This may explain Feeding & Recovery
the inconsistent results obtained in the production of (14–30 days)
all‐male O. niloticus × O. aureus progeny. Some observa-
tions have been made with respect to the effect of tem- Figure 18.4 Reproductive cycle of Oreochromis species.
perature on tilapia sex determination. Exposure of O.
niloticus fry to high temperature (34–35 °C) results in the females eat little. Finally, the hatched fry are released
significant sex reversal in both directions, whereas that in shallow waters. The female then resumes active feed-
of O. aureus results in masculinisation. Another case is ing, which allows maturation of oocytes in her ovaries.
O. niloticus × O. aureus, a commercially‐produced hybrid After a further 3–4 weeks, she is ready to spawn again.
in Israel. Because of its cold tolerance and, therefore, cul-
ture at relatively low temperatures, significant declines Female tilapias lay their eggs in multiple batches.
in the proportion of males have been observed in succes- Typically, a female lays 8–12 batches per year under
sive generations. The speculation that temperature favourable temperature conditions. In the case of
dictates the sex of tilapia, however, remains controver- Oreochromis species, each batch contains about 1000–
sial. Steroid hormones have perhaps the most significant 2000 eggs. The eggs are large (3–5 mm), heavy and
effect on sex determination in tilapias as well as in many contain sufficient yolk to supply nutrients to newly
other fish. Apparently there is an age (10–15 days post hatched fry for up to 5 days.
hatch) in the development of these species during which
the sex is determined by the level of androgenic and oes- To boost broodstock productivity, the time between
trogenic hormones circulating in the body. Exogenous two successive spawnings may be considerably short-
administration of a specific hormone or its analogue ened by removing the fertilised eggs from a female’s
during this labile period will therefore result in the mouth (Figure 18.5). Once the clutch of eggs is removed,
production of monosex stocks (see section 18.5.2). the female assumes that the eggs are lost, starts feeding
and quickly returns to reproductive mode. This is similar
18.4.2 Reproductive Biology to removing eggs from a chicken to encourage it to lay
more eggs. The eggs removed from the females are incu-
All tilapia species mature early (4–6 months) and repro- bated and hatched in down‐welling jars. After eggs hatch,
duce year‐round under suitable environmental condi- the yolk‐sac larvae are then reared in shallow trays with
tions. Tilapias are perhaps the only major group of fish in clean flowing water under controlled conditions that
aquaculture that breed in captivity without any special ensure high survival of eggs and fry making mass‐scale
inducement or modification to their environment. production of uniform seed possible.
The most common tilapia species, O. niloticus, reaches
sexual maturity at a size of 30–40 g. When mature, 18.5 Control of Reproduction
tilapias can spawn year‐round if the water temperature
stays between 24–35 °C. Typical breeding behaviour of As mentioned in section 18.1, early maturation and pro-
Oreochromis species is shown in Figure 18.4. lific spawning of tilapias in grow‐out systems present
two major problems for tilapia farmers. First, physiolog-
When a mature Oreochromis female is ready to ical energy resources are directed to the processes of
spawn, she visits the breeding arena or ‘lek.’ The breed- sexual maturation and reproduction and become una-
ing arena consists of several males that form well‐ vailable for somatic growth. Second, continuous recruit-
defended, individual nests. After brief courtship, the ment of young tilapias into the grow‐out system results
female lays her eggs while the male simultaneously fer- in increased competition for resources such as space and
tilises the eggs. The female then picks up the fertilised food. A number of methods have been developed to
eggs in her mouth for brooding and leaves the arena. control tilapia reproduction and recruitment. The most
Intensive parental care continues until the fry are large successful methods involve production of all‐male
enough to be on their own. The female stands guard stocks because males grow faster than females in almost
over the free‐swimming fry. If the fry are threatened, all tilapia species.
they return to their mother’s mouth until the threat
passes. Mouth brooding lasts for 3 weeks, during which
398 Aquaculture
Uro-genital pore Anus Ureter Oviduct Anus
Figure 18.6 Male (left) and female (right) tilapia genital papillae.
Figure 18.5 Clutch removal: removing fertilised eggs from a 18.5.1.2 Hybridisation
female O. niloticus mouth in a hapa‐based hatchery. Source: The use of hybridisation to produce all‐male populations
Reproduced with permission from Victor Suresh, 2017. was considered in section 18.4.1.
18.5.1 Monosex Tilapia Production 18.5.1.3 Hormonal Sex Reversal
18.5.1.1 Hand‐sexing General techniques for hormonal sex reversal in fish
Tilapias display distinct sexual dimorphism as they were outlined in Chapter 7 (section 7.8.3). Most com-
become juveniles. The males and females are differenti- mercial all‐male tilapia stocks are produced by treating
ated by means of their genital morphology (Figure 18.6). tilapia fry with synthetic androgens, particularly 17α‐
Males have a single longer and pointed opening which methyltestosterone (MT). The most commonly used
serves as the urogenital pore. Females have two round protocol is to incorporate MT into the fry diet at 60 mg/
openings, one for urinary excretion and another for kg by first dissolving it in 95% ethanol. The MT‐treated
expulsion of eggs in the urogenital papillae. feed is then fed to fry from the first feeding stage for 21
days. Seed stock with 99–100% males can be obtained if
This differentiation becomes more obvious when the the protocol is strictly adhered to. The method is popu-
fish are 10 g and larger. The typical practice is to sex tila- lar because it is the most effective way of controlling the
pia individually before stocking for grow‐out and to select reproduction in grow‐out ponds. In addition, it enhances
only the males for stocking. As this process is labour growth and converted males also grow faster than origi-
intensive and results in wastes of about 50% (females) nal males. Using hormonal sex‐reversal techniques, a
seed, it is rarely practised these days. single hatchery can produce and supply over 30 million
sex‐reversed fry per month (Bhujel, 2014).
Other synthetic androgens such as fluoxymesterone
and trenbolone acetate are also highly effective in pro-
ducing all‐male tilapia stocks. However, MT is the most
popular and widely used androgen. Instead of adding to
the diet, the hormones can also be applied as a dip. Use
of ultrasound at the time of androgen dip application has
shown improvements in masculinisation success, but
this method produces highly variable results and is still
being developed. Use of hormones in sex reversal has
evoked environmental and food safety concerns because
of the potential for hormones to enter water bodies and
the human food chain.
18.5.1.4 Genetic Manipulation
Genetic manipulation of tilapias to produce either mon-
osex or sterile stocks has nearly a 30‐yr history. The
method has been tried as an alternative to hormonal sex
reversal. Triploidy, gynogenesis and androgenesis are
commonly used techniques that have been applied in the
commercial production of tilapias. These techniques and
their benefits and uses are described in detail in sec-
tion 7.8. Chromosome manipulation techniques are not
appropriate for routine production of sterile or monosex
stocks because it is difficult to induce 100% triploidy,
gynogenesis or androgenesis on a commercial scale. Tilapias 399
Furthermore, growth and survival of triploid, gynogenic
and androgenic fish are generally inferior to that of nor- conditions and economic factors. The simplest and
mal diploids during early life stages. cheapest method is to use fingerlings that result as the
by‐product of tilapias grow‐out in ponds or tanks. Any
18.5.1.5 Production of Genetically system that uses both sexes of a tilapia species in grow‐
Male (YY) Tilapias out will inevitably produce tilapia seed as a result of
Production of genetically male tilapias eliminates the natural reproduction. Although reliable technologies
need for using hormones to mass produce tilapia seed. are available to control reproduction through the pro-
The method, however, requires the use of hormonal sex duction of all‐male stock, many small farmers still use
reversal at the initial stages of broodstock development. mixed‐sex stocks in tilapia grow‐out ponds. For them,
It is a laborious and time‐consuming method because of the fingerlings produced in their grow‐out ponds are
the extensive progeny testing involved. But, once a brood- free of cost which can be used to stock for further grow‐
stock population is founded, it can be used in any hatch- out. Some farmers sell to other neighbouring farmers as
ery system by replacing normal males with YY super‐males an additional source of income. Use of mixed‐sex seed is
(section 7.8.3, Figure 7.10). Hatcheries should then exer- good for the farmers who practice partial harvests. This
cise sound broodstock management practices to prevent system of collecting fry, however, has many drawbacks,
genetic contamination of the YY stock. Commercial mainly inefficiency and unreliable supply of uniform‐
stocks of genetically male tilapias are now available; size seed. Some farmers apply hormonal sex reversal,
including the pioneering stock produced by Fishgen Co. but it has very low success rate with the fry collected
Ltd, together with University of Wales, Swansea. This from the ponds. As a result of this inefficient system,
stock has been shown to outperform equivalent mixed‐ development of refined and specialised seed production
sex tilapias (Beardmore et al., 2001). However, results are systems has taken place. These systems may use open
inconsistent and vary from country to country. ponds, tanks or net cages (hapas) in ponds or large water
bodies (Table 18.6).
18.5.2 Recruitment Control
Many resource‐poor farmers choose culturing mixed‐sex 18.6.1 Pond Systems
population of tilapias because of lack of access to reliable
technology to produce 100% monosex population. They Earthen ponds are widely used in the production of
may also prefer to raise mixed‐sex tilapias to produce tilapia fry or fingerlings. The ponds are typically small
their own seedstock for future stocking. To prevent (0.01–0.1 ha) and well‐managed with fertilisation, water‐
over‐p opulation during culture, predators that eat newly level control and careful feeding. Brood fish are stocked
recruited tilapia fry and fingerlings may be used. A num- at low densities (0.5–1 tilapias/m2) with a male‐to‐female
ber of predator species have been tested, including s eabass ratio of 1 to 2–3. Fry and fingerlings are netted out on a
(Lates calcarifer), walking catfish (Clarias spp.), snake- periodic basis (daily, weekly or biweekly). This type of
head fish (Channa spp.), Nile perch (Lates niloticus), mah- system may yield fry at a rate of 0.1–3/m2/day. The fol-
seer (Tor spp.) and some South American cichlid species. lowing factors influence fry yield in pond systems:
To be used reliably, this method requires optimisation of 1) Pond size. The smaller the pond, the better it can be
predator–prey ratios, timing of predator release, number managed and harvested, and therefore this increases
and size of the predator at release. However, it has not its productivity. Ponds of < 1000 m2 are preferable.
achieved much success. Some farmers continue to practice
this method because the predator species fetch higher 2) Harvest interval. More frequent harvests result in
prices in local markets and also some farmers want to removal of the larger seed, thereby reduces cannibal-
reduce the risks by diversifying the species. Also, by waiting ism of younger fry.
until after recruits are produced, the physiological energy
has already been expended by the breeding adults. 3) Stocking density. Lower stocking density typically
Therefore, the growth of stocked tilapias will be hampered. improves broodstock efficiency and produces
larger seed.
18.6 Seed Production
No matter how frequently and efficiently fry are har-
Systems to produce seed stock for tilapia culture vested from breeding ponds, it is practically impossible
vary from location to location depending on local to remove all fry from a pond, which becomes overpopu-
demand for seed, geographic conditions, environmental lated with recruits from early spawns. This results in
increased competition for food and space, which dimin-
ishes seed output. To overcome this problem, the breed-
ing ponds have to be periodically drained to remove all
fish. An alternative to this practice is to seine the pond
and remove all broodstock, which are then transferred
400 Aquaculture
Table 18.6 Comparison of various representative hatchery systems to produce tilapia fry.
Species Pond Tank Hapa
Location
System size (m2) O. niloticus Florida red tilapias O. niloticus
Stocking density (no./m2) Philippines Bahamas Thailand
Size (g) 300–500 34 40, 60 or 120
1 7 6
Sex ratio (F:M) Male and female Male and female 143 Female 100–300, male 100–400
Harvest strategy 50–100
3:1 3:1 1:1 or 2:1
Fry output (no./m2/day) Harvest of fry, Clutch removal every 15–16 Clutch removal every 5–7 days
Female productivity (fry/kg twice per day days and artificial incubation and artificial incubation
female/month) 0.7 91.7 108–141
Source 82.9 3021 3,180
Guerrero (1986) Watanabe et al. (1992) Bhujel (2000); Bhujel et al. (2001)
to another pond. The fry left in the pond are further (Figure 3.6). Brood fish are stocked inside the hapa. Eggs
nursed to a size suitable for stocking. Another alterna- and larvae are regularly collected by means of clutch
tive, practised in Israel, is to construct breeding ponds removal. The hapa can also be designed to have two
with two compartments: a spawning compartment and a nested compartments. The inner compartment has a
fry‐collecting compartment that is built at a lower level mesh that retains the broodstock but allows the fry to
relative to the spawning compartment. The two com- swim to the outer compartment, which is composed of
partments are separated by a sluice gate that retains the fine‐mesh netting. The inner cage, with brood fish, is
broodstock and allows collection of fry with minimal removed every 10–15 days and the fry collected in the
handling. outer cage are allowed to grow to a size suitable for
stocking.
18.6.2 Tank Systems
Concrete, plastic or fibreglass tanks are also used in The pioneering hapa‐based system developed at the
tilapia breeding. A higher degree of control over the Asian Institute of Technology (AIT), Thailand, was
broodstock and seed, as well as the spawning environ- described by Bhujel (2000, 2014) (Figure 18.7). The sys-
ment, is a major advantage (section 18.5.1) in the use tem employs either 40, 60 or 120 m2 size hapas, in
of tanks as breeding systems. Practices such as which male and female tilapia are stocked at 1:1–2 ratio
clutch removal and broodstock reconditioning, which and 5–6 fish/m2 density. Egg removal from the mouths
improve hatchery efficiency, can be implemented in of incubating females is done by gathering them in a
tank‐based systems with relative ease. Tank systems are corner of the hapa. Seed production in the hapas is
typically used when water or land resources are limited. over 100 fry/m2/day. Thousands of private hatcheries
This is because of their high seed output per unit of around the world, especially in Bangladesh, Brazil,
water and land area. The main disadvantage of tank China, Philippines, Thailand and Vietnam, presently
systems is the high cost of initial investment to con- use this system.
struct them.
Keeping broods in hapas helps to maintain the purity of
18.6.3 Hapa Systems stocks. It is cheaper than tank culture, and also flexible. A
Hapa‐based breeding systems provide some of the major disadvantage of the hapa system is that the mesh
advantages of tank‐based systems at a lower cost. A hapa openings (pores) of the hapas are easily fouled. This lim-
is a cage made of netting that can be suspended in ponds, its water exchange and supply of natural food organisms.
tanks or large water bodies such as lakes and reservoirs So, hapas must be pulled out of the water periodically
(once a month is recommended) and sun‐dried for a day
or so then washed. This is a labour‐intensive practice, but
it provides opportunities to rest and recondition the
broodstock, thereby improving productivity.
Tilapias 401
Figure 18.7 Net cages (hapa) used for tilapia fry production. Source: Reproduced with permission from Victor Suresh, 2017.
18.7 Nutrition, Feeds and Feeding Crude protein digestibility and assimilation efficiency of
plant matter (filamentous and planktonic green and blue‐
Thorough reviews of nutrient requirements and feeding green algae) ranges from 50% to 80%.
management of farmed tilapias can be found in Lim and
Webster (2006) and Ng and Romano (2013). 18.7.2 Nutrient Requirements
18.7.2.1 Protein
18.7.1 Diet and Feeding Habits Like most fish species, tilapias require a high concentra-
While tilapias in general are opportunistic omnivores, tion of dietary protein when they are young. Various
there is considerable specialisation in diet in some spe- assessments have reported a wide range of 30–55% crude
cies. Young tilapias are carnivorous and prefer zooplank- protein requirement for young tilapias. What is clear is
ton. As they become juveniles, their diets shift to plant that the protein level required for adult tilapias is a lot
material or detritus of plant origin or both. Phytoplankton, lower than for fry. Field studies show that adult tilapias
benthic algae, macrophytes and periphyton are common grow well when feeds containing 25–35% crude protein
natural foods of tilapias in nature. Oreochromis species are used. In green water ponds with abundant plankton,
feed primarily on microscopic plant materials, whereas 25% crude protein diets are adequate, but for cage and
Tilapia species prefer large plants. Tilapias use a wide tank culture, diets containing 30–35% crude protein are
variety of feeding methods, including visual feeding, suc- required. Feeds containing higher protein levels do not
tion feeding, biting and grazing. add any substantial value in terms of growth. The recom-
mended levels of protein in the diet range from 40–45%
The primary method of feed intake in adult tilapias, for fry to 25–30% for grow‐out, with brood fish requiring
particularly in Oreochromis species, is continuous suc- a slightly higher level (25–35%) than fish intended for
tion, in which food particles are entrapped by filtration as grow‐out (Bhujel, 2014). There may be considerable dif-
water is passed over the gills. The food particles are ferences in nutrient requirements and utilisation among
crushed by the pharyngeal bones and then passed into the different strains of tilapia. Fast growing tilapias—such as
alimentary tract. Tilapias possess a stomach that can reach the GIFT strain—have higher feed intake and feed effi-
extremely acidic conditions (pH < 1) in proportion to the ciency, and utilise diets containing higher protein levels
stomach fullness. This acidic condition lyses plant cells better than the red hybrids.
and prepares food material for further digestion in the
intestine. Tilapias have a long, coiled intestine. Intestinal 18.7.2.2 Energy
pH is 6.8–8.8 and conducive to the action of digestive Although a feed that meets the protein requirements of
enzymes such as trypsin, chymotrypsin and amylase. tilapias is also likely to meet the energy requirements,
Anaerobic fermentation may also occur in the hindgut.
402 Aquaculture 18.7.2.5 Vitamins
The need for vitamin supplementation in semi‐intensive
balancing protein and energy is important in optimising pond culture of tilapias is questionable, because natural
feed cost relative to growth and other production param- foods are rich in many vitamins. However, complete
eters. Optimal protein–energy ratio in tilapias is 110– feeds for tilapias in intensive systems, particularly indoor
120 mg protein/kcal energy when the fish are young. tank systems, require comprehensive vitamin supple-
This is decreased to about 100 mg protein/kcal energy as mentation (0.25–1% of the feed depending upon type of
they grow and reach adulthood. premix) of the kind that is used in complete feeds for
other fish in intensive culture (see section 8.4.5).
Lipids and carbohydrates are cheaper sources of energy
than protein. In general, warm‐water omnivores such as 18.7.3 Feeds and Feeding
tilapias utilise carbohydrates better than lipids. Dietary 18.7.3.1 Feedstuffs
lipid levels above 12% cause reduced growth rates in Tilapias are capable of utilising a wide variety of feed-
tilapias probably due to reduced feed intake, whereas stuffs either as a single feed or as a part of compound
digestible carbohydrates as high as 40% are well utilised. feed. Feedstuffs that are fed to tilapias in extensive grow‐
Among carbohydrates, starch and dextrin are better out systems include rice bran and various other grain
utilised than glucose, whereas cellulose and other fibre by‐products; oil seed residues or oil seed cakes, aquatic
components are not digestible. Inclusion of fibre above and terrestrial plants; and kitchen wastes.
5% causes depressed growth in tilapias.
Numerous feedstuffs, including some of those above
18.7.2.3 Lipids and Fatty Acids plus various animal by‐products, tubers and fermenta-
As noted above, tilapias do not appear to effectively use tion by‐products, are used in compound feeds. Protein
lipids as an energy source. Thus, suggested maximum and energy digestibility for these feedstuffs ranges
lipid levels in the diet for tilapias range from 5% to 12%. between 30% to more than 90% (Ng and Romano, 2013).
Excess lipids also result in substantial carcass and vis- Obviously, based on this range, some feed ingredients
ceral deposition of fats. Vegetable oils such as corn oil are clearly preferred. Other factors that influence the
and soybean oil are superior sources of lipids compared choice of feed ingredients used in feed formulations are
to animal fats. It appears that tilapias require low levels cost, fibre content, amino acid profile, palatability, the
(»1% or less) of linoleic acid (18:2n‐6) and linolenic acid presence or absence of toxins, and the presence or
(18:3n‐3) in their diet. absence of digestive enzyme inhibitors.
18.7.2.4 Minerals Table 18.7 shows examples of some feed formulations
In the typical hard water used in aquaculture, there is for tilapias. Once considered essential, inclusion level of
sufficient calcium to meet the calcium requirements of fishmeal has declined from over 10% to 3% in tilapia feeds.
tilapias. In soft waters, dietary calcium is required. Some tilapia feeds have even been formulated without any
Similarly, a dietary supply of magnesium is important in fishmeal and still perform optimally in most culture sys-
waters that are low in this ion. A summary of nutrient tems. This is a major advantage of tilapias for aquaculture.
requirements, including the minerals, was provided by
Bhujel (2014).
Table 18.7 Model tilapia feed formulations based on ingredient availability and costs in the USA.
Ingredient Semi‐intensive ponds Intensive ponds Intensive tanks
(26% protein) (32% protein) (36% protein)
Soybean meal 38.3 48.5 50.8
Wheat middlings 4 20 18
Fishmeal 4 6 12
Corn 50.8 22.6 16.5
Dicalcium phosphate 1 1 0.8
Vegetable oil 1.5 1.5 1.5
Vitamin mix 0.2 0.2 0.2
Mineral mix 0.2 0.2 0.2
Source: Modified from Lovell (1998) with permission from Kluwer Academic Publishers.
18.7.3.2 Feed Forms and Sizes Tilapias 403
Tilapias accept feeds as dry meal, moist meal and pellets.
Although dry meal is suitable for feeding to fry, neither not sufficient to sustain growth, so complete feeds
dry nor moist meals are appropriate for feeding to larger are required for further growth. As stocking densities
fish in intensive culture systems. A considerable portion increase, growth plateaus occur with smaller sizes of
of such feeds is wasted. Complete feeds that incorporate fish, so that complete feeds must be introduced earlier
high‐quality ingredients must be pelleted or extruded to in the culture cycle. The potential of complete feeds to
minimise waste. Such processing also enables easy han- increase growth of tilapias in semi‐intensive pond cul-
dling, storage and distribution of the feed by the farmer. ture was demonstrated by Edwards et al. (2000) in a
study where O. niloticus juveniles of ca. 25 g initial
Particle size is an important consideration in selecting weight were stocked at 4/m2 in 200‐m2 fertilised ponds
feeds for tilapias, which prefer smaller feed particles than for 4 months. The ponds were subjected to one of the
many other cultured fish species. Unlike other species following treatments:
that swallow whole feeds, tilapias tend to chew large par- ●● (F): fertilisation (4 kg N urea + 2 kg P triple superphos-
ticles. These are repeatedly taken into the mouth and
ejected until they are reduced to an appropriate size. phate, TSP);
This results in leaching of the nutrients and wasting of ●● (F + E): fertilisation + energy (pelleted cassava starch +
feed. Table 18.8 presents the appropriate particle forms
and sizes recommended for feeding tilapias of different lipid);
body sizes. ●● (F + E + Pr): fertilisation + energy + protein (fishmeal
18.7.3.3 Feed Input and soybean meal);
The extent to which natural foods are available to tila- ●● (F + E + Pr + P): fertilisation + energy + protein + phos-
pias influences the amount and quality of feed input. In
ponds, the amount of natural foods available to individ- phorus (as dicalcium phosphate);
ual fish depends on a number of factors such as soil fer- ●● (F + E + Pr + P + V): fertilisation + energy + protein +
tility, the type and the amount of fertilisers added, and
the number and weight of fish stocked. Tilapias stocked phosphorus + vitamins.
at small size (<10 g) and low density (1–2/m2) typically Growth was significantly improved as each nutrient type
grow very well on natural foods, and pond fertilisation was added into the feeding protocol, except for the
may be sufficient to meet the nutrient requirements for v itamins. Average daily growth rates were:
growth. However, once they reach 40–80 g, satisfactory ●● 14 kg/ha for the (F) treatment;
growth cannot occur on natural foods alone. At this ●● 22 kg/ha for the (F + E) treatment;
stage, supplementary feeds are needed to attain good ●● 43 kg/ha for the (F + E + Pr) treatment;
growth rates. As natural foods are high in protein, feeds ●● 55 kg/ha for the (F + E + Pr + P) treatment;
rich in energy, such as rice bran, are ideal supplemen- ●● 55 kg/ha for the (F + E + Pr + P + V) treatment.
tary feeds. As the fish grow further to a larger size, The increase in growth rate with the addition of vitamins
e.g., > 300 g, natural foods and supplementary feeds are was not different to the response to being fed with phos-
phate supplementation alone; evidence that natural
Table 18.8 Feed forms and particle sizes recommended foods available to the animals in semi‐intensive culture
for tilapias. provide sufficient vitamins.
Body size (g) Particle size Recommended form 18.7.3.4 Feeding Allowance
diameter (mm) There are two options in practical feeding of fish. One is
<1 Meal to feed the fish to satiation and the other is to feed a
1–2 0.5–1 Crumbles restricted ration. Best growth is normally achieved by
2–30 1–1.5 Crumbles feeding to satiation. But satiation levels are not necessar-
30–100 1–2 Pellets/extruded ily the most economic feeding levels, because food con-
2.4 particles version at satiation levels is often poor. Also, it is difficult
100–250 Pellets/extruded to determine satiation levels in fish because food con-
3.2 particles sumption occurs in the water medium. This may lead to
250 to market Pellets/extruded overfeeding, which is wasteful and deleterious to water
size 4.8 particles quality. As a result, restricted rations are recommended
for feeding fish. The choice between satiation and
restricted feeding should be based on the protein and
energy density of the feed. Although restricted feeding of
high‐protein, high‐energy diets is beneficial, low‐pro-
tein, low‐energy diets have to be fed at satiation levels to
meet the nutritional requirements of the species.
404 Aquaculture Table 18.11 Desirable water quality for tilapia culture.
As discussed in an earlier section, natural availability Water quality parameter Desirable level
of foods also determines feed allowance, and feeding at
half satiation in fertilised ponds may produce similar Temperature 26–32 °C
growth rates and yield as that supported by full satiation Dissolved oxygen >3 ppm
feeding. Other factors that must be considered when Total ammonia <1 ppm
determining feeding allowance include: pH 6.5–8.5
1) Body size. As a fish increases in size, it is obvious that Alkalinity >20 ppm
Hardness >50 ppm
the absolute amount of feed it can consume increases. Salinity 0–20‰
However, the amount of feed it can consume per unit
of body weight decreases. Recommended feeding Reduced feeding levels are recommended whenever
allowances for different body sizes are provided in water quality problems are anticipated or encountered.
Table 18.9. Adverse weather conditions such as high winds and
2) Water quality factors. Feeding allowances presented heavy rainstorms cause changes in water quality in pond
in Table 18.8 are for tilapias grown at optimum tem- systems. Heavy algal blooms in pond systems, which may
perature conditions (26–32 °C). Feed consumption in be due to high feeding rates, can cause severe oxygen
tilapias decreases with decreasing water temperature depletion. In such events, feeding is suspended until
and ceases at 16 °C. Appropriate reductions in feeding conditions improve.
allowance will be required under such conditions
(Table 18.10). Reductions in feeding allowance are High stocking densities mean high feed input to the
also required when water temperature increases above culture system. This leads to dissolved oxygen depletion
the optimum level (32 °C). At such conditions, dis- and high ammonia levels. Stress due to poor water qual-
solved oxygen levels decrease and the toxicity of ity leads to poor feed consumption and conversion. So,
ammonia increases in culture systems. So, feeding lev- culturists using high stocking densities must use devices
els must be lowered at high water temperatures too. such as aerators and mixers or water exchange to
m aintain water quality at or above acceptable levels
Table 18.9 Feeding allowance and frequency for tilapias at different (Table 18.11). In static ponds, feed application must not
body sizes. exceed 120–130 kg/ha/day.
Body size (g) Daily feeding allowance Feeding frequency 18.7.3.5 Feeding Frequency and Time
(% of body weight) (no. of meals/day) In their natural habitat, tilapias are known to eat contin-
<1 uously through the day, so multiple feedings may be
1–5 30–10 8–12 beneficial. Fry, which eat up to 16% of their body weight
5–20 10–6 6 every day, need to be fed 8–12 times a day. This fre-
20–100 4 quency is reduced as they grow (Table 18.9). At the
>100 6–4 3–4 grow‐out stage, two or three meals per day are sufficient
4–3 2–3 for optimal growth. Daytime is the best time to feed
3–2 tilapias. In their natural habitat, they eat during the day,
with little or no feeding activity at night.
Table 18.10 Feeding allowance as modified by water
temperature. 18.7.3.6 Feeding Method
Hand feeding, although labour intensive, is considered to
Temperature (°C) % of normal daily be the best method to feed tilapias because it allows the
feeding allowance farmer to observe their feeding responses. It is essential
32–35 that the feed is distributed evenly over the water surface
24–32 80 to allow all the fish to feed. Tilapias are socially aggres-
22–24 100 sive and tend to develop social hierarchies in which one
22–20 individual dominates others and appropriates more feed.
20–18 70 Uneven distribution of feed will result in dominant indi-
18–16 50 viduals occupying places that receive the most feed and
<16 30 eventually lead to large variation in fish size at harvest.
20
No feeding
Tilapias 405
Figure 18.8 Automatic feeder used in tilapia cage farming in Vietnam. Source: Reproduced with permission from Sena De Silva, 2017.
Automatic feeders and demand feeders are useful for the yield potential of tilapias, they are important to the
feeding fish in cage culture, especially when access to farmers because they provide inexpensive animal pro-
cages is difficult or time‐consuming. They are also useful tein to the farming families and some supplemental cash
in large farms that would require extensive manpower to income.
feed the fish or when manpower is prohibitively expen-
sive. Automatic feeders are becoming widely used in 18.8.2 Semi‐Intensive Pond Systems
many parts of the world (Figure 18.8). Some farmers Semi‐intensive pond systems represent a vast improve-
use demand feeders in cages in SE Asia. The various ment over using extensive systems of production. The
methods for feed distribution in aquaculture systems are ponds are intentionally constructed for aquaculture.
outlined in section 8.8. Stocking as well as harvesting is planned. Seed is produced
on the farm or purchased from specialised hatcheries.
18.8 Grow‐Out Systems Methods to control reproduction in grow‐out are applied.
As in other semi‐intensive pond culture, fertilisation of
18.8.1 Extensive Systems ponds is carried out. Feeds, prepared on‐farm or at a feed
Extensive systems for tilapias include a broad range of mill, are used. Annual yield typically ranges from 3–6 t/ha,
culture units and practices, including backyard ponds, but some well‐managed systems may yield up to 10 t/ha.
roadside ditches, irrigation canals, reservoirs, rice fields The majority of global tilapia production comes from
and wastewater treatment ponds (Table 18.2). These sys- semi‐intensive pond systems.
tems are mostly located in the tropics and operated by
poor rural farmers for their subsistence livelihoods. They Semi‐intensive tilapia culture systems can be used
use basic aquaculture technology and under‐utilised effectively to satisfy the needs of subsistence farmers as
land, water or other facilities. Stocking is irregular and well as the increasing desire of small‐scale farmers to raise
may consist of small tilapias harvested from the wild. No production and to increase cash income. Considerable
intentional fertilisation or feeding is carried out and research has been directed towards understanding the
annual yields are normally below 1 t/ha. Although such scientific basis of fish and primary productivities in semi‐
systems are quite under‐productive when compared to intensive tilapia pond systems, and it has resulted in a vast
improvement of our knowledge of optimising pond inputs
such as fertilisers and feeds.
406 Aquaculture for supplementary feeding in semi‐intensive pond cul-
ture of tilapias:
18.8.2.1 Pond Fertilisation
Tilapias can be grown inexpensively by applying fertilis- 1) Provision of feeds that complement the natural pro-
ers in pond to enhance the growth of natural foods (sec- ductivity of the ponds. In this approach, the animals
tion 4.4.2). However, the ideal levels of nitrogen (N) and are provided with supplementary feed (0.5–2% bio-
phosphorous (P) in pond water to sustain production of mass) throughout the grow‐out period.
phytoplankton are difficult to estimate. In general, an
N/P ratio of 10:1 is recommended because this is the 2) Commencement of feeding once fish growth plateaus
ratio between nitrogen and phosphorus in most phyto- on natural foods alone. Beginning feeding at a
plankton. An N level of 1.3 ppm and P level of 0.15 ppm is moderate size (100–200 g) may be more economical
recommended by some. Others favour a higher level of N than feeding throughout the grow‐out period starting
(15–30 N to 1 P) to discourage the growth of nitrogen‐ at smaller sizes.
fixing blue‐green algae, which are low in nutritive value
to fish, and to encourage the growth of green algae and 18.8.3 Polyculture
diatoms, which have a high nutritive value. Daily loading
rates of 4 kg N/ha and 1 kg P/ha are optimum for semi‐ Polyculture of tilapias with other fish species is practised
intensive tilapia ponds. Daily N loading rates higher than in many countries (Wang and Lu, 2016). Traditional
4 kg/ha, however, may be counter‐productive as ammo- polyculture is based on the premise that various species
nia may increase to toxic levels. Phosphorus is added at a stocked together utilise different trophic niches that
relatively high rate (1.5–2 kg P/ha/day) to new ponds exist in a pond and therefore produce more biomass than
because P is rapidly lost to pond soils. The high level of P if they were stocked alone in monoculture (section 2.3).
fertilisation is also applicable to ponds in acid‐sulphate Tilapias have been grown with carps in the Asian
soils to compensate the loss due to sequestering action polyculture systems (extensive and semi‐intensive
of the soil. ponds) for many decades. Similarly, tilapias have been
grown along with common carp in semi‐intensive pond
The recommended levels of N and P may be applied systems in Israel. When shrimp monoculture in South
in the form of organic fertilisers, such as livestock and Central America was affected by a number of viral
manures or crop residues, or as inorganic fertilisers. diseases in 2000s (sections 10.5.2.1 and 21.1.2) tilapias
Manures have traditionally been used in Asian aquacul- were stocked with shrimp in brackish water ponds.
ture as fertilisers. Manures contribute other trace Reduced incidence of shrimp diseases in ponds stocked
elements in addition to supplying N, P and C. with tilapias is attributed it to the role of tilapias in
Furthermore, they also play a role in the detrital food stimulating algal and bacterial populations that improve
chain. However, the levels of N and P and the N/P ratio water quality in shrimp ponds.
of most livestock manures are way below the require-
ment. Excessive application of manures is required to The suitability of a given species in polyculture
fulfil the requirements that may result in severe oxygen depends on its compatibility with other species, and
depletion in the water and accumulation of organic tilapias have been shown to be compatible with some
matter in the pond bottom, which ultimately reduces carp and other fish species. However, in polyculture, tila-
yields. So, it is recommended that ponds are fertilised pias and other fish species are stocked at low densities:
with livestock manures at lower rates together with 5000–10 000 fish/ha compared to 30 000–40 000 fish/ha
inorganic fertilisers to compensate for the nutrient are stocked in semi‐intensive monoculture of tilapias.
deficiency. One particular strategy that has proved Some studies and field experience suggest that tilapias
effective is to apply chicken manure at a rate of 200– are not appropriate species for polyculture at high
250 kg (dry‐matter basis)/ha per week and to supple- densities. Tilapias are typically more aggressive in their
ment it with urea and TSP at weekly rates of 28 kg N/ha feeding and tolerate crowding and poor water quality
and 7 kg P/ha, respectively. At a stocking density of conditions better than most tropical aquaculture species.
three tilapias/m2, this fertilisation regime provided an
extrapolated annual net yield of 8–11 t/ha. When tilapias fetch attractive prices in the local or
export markets, it is probably more profitable to grow
18.8.2.2 Supplementary Feeding them at high densities in monoculture than at low
The rationale and principles of supplementary feeding densities in polyculture. In many countries, such as
have been covered in detail above (section 18.7.3). Taiwan and Israel, tilapia farming began as polyculture
Supplementary feeding is important in semi‐intensive but has eventually developed into intensive monoculture.
pond culture of tilapias, and most nutrients required in Tilapia polyculture is more desirable, however, when a
complete feeds are also required in supplementary feeds farmer requires production of a variety of species for the
(Edwards et al., 2000). In practice, there are two options market and where the other species used in polyculture
Tilapias 407
Figure 18.9 Tilapia culture integrated with duck houses in Zambia. Faeces and uneaten food fall, or are washed, into the ponds housing
tilapia. Source: © FAO Aquaculture photo library.
also fetch an attractive price. In rural Southeast Asia, integrated system in Thailand, and much of the produc-
polyculture of tilapias with Indian carps and silver barb tion was attributed to the inefficient feeding of ducks
is practised because the latter also fetch an attractive that resulted in feed wastage. In rural Nigeria, small
price in the local markets. In Bangladesh, almost all farmers fertilise their tilapia ponds with excreta from
grow‐out farmers raise tilapias in polyculture with Indian their chicken farms. The ponds serve an important pur-
carps and pangasius catfish for the same reason. Some pose in being the source of water for the farm crops and
carnivorous species such as sea bass, snakehead and for poultry in the dry season. Ponds integrated at 1000
walking catfish are also grown in polyculture with tila- chickens/ha received an excreta load of 3600 kg/ha/
pias with a view to controlling tilapia recruits (sec- month (dry‐matter basis), which resulted in an extrapo-
tion 18.5.2), and at the same time to generate additional lated net yield of 18.25 t/ha of an African catfish species
income from them. and 14.9 t/ha of O. niloticus. Integrated aquaculture
practices are further discussed in Chapter 2 (section 2.4).
18.8.4 Integrated Farming
Tilapias play an important role in integrated agriculture– 18.8.5 Intensive Pond Systems
aquaculture systems in Asia. Integration of tilapia farm- Semi‐intensive pond systems in the tropics are typically
ing with pig, chicken and duck production systems is stocked at a rate of 2–5 fish/m2, and they yield an average
practised mostly in China and SE Asia. Typically, hous- of 3–6 t/ha per crop, as previously indicated. In areas
ing for the livestock is constructed adjacent to or above where land or water or both are limited, or climatic con-
the tilapia ponds (section 2.4; Figure 18.9). The pond, ditions restrict the growing season to less than a year, it
therefore, receives manure, urine and uneaten feed from is desirable to achieve very high productivity by using
the livestock system on a regular basis. An extrapolated higher stocking densities. Experimental culture of tila-
net fish yield of 10 t/ha/yr was reported in a tilapias/duck pias in earthen ponds at stocking densities of 5–10/m2
408 Aquaculture
Figure 18.10 Nile tilapia culture at Ranupakis Lake, Lumajang, East Java, Indonesia. Source: W.A. Djatmiko 2007. Reproduced under the
terms of the Creative Commons Attribution Share Alike license, CC‐BY‐SA 3.0, via Wikimedia Commons.
has demonstrated that intensive tilapia farming is feasi- of using cages for tilapia grow‐out is that it minimises
ble in earthen ponds. Such intensive pond systems, how- unwanted recruitment as most eggs drop through the
ever, must be managed to maintain adequate water bottom of the cages (although the stock are still engaged
quality, otherwise significant retardation in growth and in energy‐wasting reproduction). Commercial cage cul-
food conversion will occur. For management purposes, ture of tilapias is rapidly expanding in China, Colombia,
the ponds must be small (<0.5 ha) and designed to drain Bangladesh, Brazil, Indonesia, Thailand, the Philippines,
and fill effectively within a short period. Aerators are Vietnam and many other countries (Figure 18.10).
used to maintain desirable dissolved oxygen levels, espe- Reservoirs built for irrigation and hydroelectric power
cially during the critical late night and early morning generation are used in many locations to grow tilapias
hours. Adequate circulation of the water must be pro- sustainably in cages (Moura et al., 2016).
vided to minimise accumulation of organic waste in the
pond bottom. There may also be daily exchange of a part The cages may be made of locally available bamboo,
of the water to remove organic debris accumulating on netting, etc., or constructed from commercial‐grade
the pond bottom. In Israel and Taiwan, where intensive materials such as PVC and steel floated with plastic or
pond systems were developed, the production systems iron drums. A wide range of cage sizes are used. But large
are connected to a large reservoir that serves as a water cages (>1000 m3) are hard to manage. Such cages are typ-
treatment body. Wastes accumulating on the bottom of ically stocked at 20–25 tilapias/m3 and yield about 1 kg
ponds are flushed into the treatment ponds, rivers or fish/m3 per month. For intensive production, smaller
reservoirs periodically by means of water exchange. cages (>500 m3) are preferred and stocking densities are
Tilapias and carps are stocked in the reservoir at low usually more than 100 tilapias/m3. The typical yield in
densities to harvest the algae and thereby reduce nutri- such systems exceeds 2 kg fish/m3 per month. In Asia,
ent load in the water. Yields ranging from 10 to 30 t/ha the most common cages are either 5 m × 5 m or 6 m × 4 m
per crop are possible in intensive pond systems. with a depth of 2–3 m. Farmers stock 40–100 fish and
harvest 20–40 kg fish/m3 in about 5–6 months.
18.8.6 Cages 18.8.7 Raceways, Tanks and Water Recycle
Cages provide the opportunity to grow fish in manageable Systems
units in small to large public water bodies such as lakes, Intensive culture of tilapias in raceways is practised
reservoirs, and the open ocean, as well as running water when there is an abundant supply of gravity‐fed running
bodies such as rivers and irrigation canals. An advantage water. There are a handful of commercial projects in
Central America which grow tilapias in raceways. The Tilapias 409
source of water includes rivers, irrigation canals and res-
ervoirs for hydroelectricity generation. The raceways are Alternatively, it may involve a sophisticated recirculating
typical of this culture system, being generally long and system with components for the removal of solid waste,
narrow, concrete‐lined and having water exchange rates soluble nitrogenous compounds, addition of oxygen, and
in the range of 300–2400% per day. High stocking den- disinfection of the water. These systems are generally
sity (>50 fish/m3) and biomass (>20 kg/m3) are used. used in temperate regions of the world, particularly the
Typical yields of more than 40 kg/m3 per 6 months are USA, for commercial production of tilapias. In many
possible in raceway systems. Raceways may also be used cases, the water for these systems is derived from either
for intensive rearing of tilapias in arid regions where lim- geothermal springs or power plant effluents. The sys-
ited water supply has to be utilised for multiple purposes tems are generally housed within a greenhouse or a
(Figure 18.11). s imilar enclosure to conserve heat. Systems may also be
coupled with hydroponic production of vegetables,
Rectangular, square, octagonal or circular tanks, lined such as lettuce or tomato, which takes advantage of the
with concrete or plastic, are also used in intensive tilapia nutrient‐rich effluents from the tilapia culture units.
farming (Figure 18.12). Stocking densities and yields are
as high as those in raceway systems, but the tank systems 18.8.8 Growing Tilapias in Saline Waters
are commonly used in conjunction with a water recircu- The ability of tilapias to tolerate and grow in saltwater has
lation system to minimise water use. The recirculation resulted in the development of commercial tilapia grow‐
system may involve exchange with an extensive pond for out systems that utilise brackish or seawater (Suresh and
waste removal as described earlier in section 18.8.5. Lin, 1992). Although semi‐intensive culture of tilapias in
Figure 18.11 Net‐partitioned raceways to raise tilapia fingerlings. Source: Reproduced with permission from Dr S. R. Alballaa, 2017.
410 Aquaculture
Figure 18.12 Concrete tanks for growing tilapias intensively in Saudi Arabia. Source: Reproduced with permission from Dr S. R. Alballaa,
2017.
brackish water ponds is now widely practised in Egypt, has been a steady increase in the incidence and severity
Ecuador, and the Middle East, there are only a handful of of diseases in intensive tilapia culture systems during the
projects of experimental nature involving intensive tila- last few years. Common infectious and parasitic diseases
pia culture in seawater in the Caribbean islands and the of tilapias are discussed in general texts on tilapia aqua-
Middle East. Tilapias cultured in these systems have culture (Beveridge and McAndrew, 2000; El‐Sayed,
achieved growth rates and yields that are similar to tilapia 2006; Lim and Webster, 2006); bacterial and viral dis-
cultured in equivalent freshwater systems. In Ecuador, eases of tilapias are presented in detail by Plumb and
tilapias replaced, or supplemented shrimp stocked in Hanson (2011).
brackish water ponds when shrimp monoculture was
affected by various viral diseases. Tilapia production in 18.9.1 Bacterial Diseases
shrimp ponds grew so rapidly in late 1990s that Ecuador Streptococcosis due to Streptococcus species, particularly
became the largest supplier of fresh tilapia fillet to the S. iniae, and S. agalactiae, has emerged as a serious threat
USA market in 2000. Average tilapia yield in brackish to intensive farming of tilapias worldwide. Infection
water ponds is 7 t/ha achieved in 370–408 days. results in septicaemia and neurotropic disease and causes
cumulative mortality ranging from 30 to 50%. Early clini-
18.9 Disease Management cal signs are anorexia, lethargy, loss of orientation and
erratic swimming. Later, the fish exhibit exophthal-
Tilapias are far more tolerant of adverse water quality mia, and deformed back and haemorrhages in the
conditions and other stress factors and are less prone to periorbital intraocular area and base of fins and perianal
diseases than most other cultured fish. However, there region. Adverse changes in water temperature are usually
associated with the onset of disease. Parasitic infections Tilapias 411
predispose fish to streptococcal infections.
18.9.3 Fungal Diseases
Motile Aeromonas septicaemia due to Aeromonas Secondary infections due to the water mould Saprolegnia
hydrophila and related species is another common dis- parasitica are common in many fish species, including
ease of tilapias. Clinical signs include frayed fins, haem- tilapias. Infections occur after injury and particularly
orrhaged skin and fins, inflamed skin and fins, scale when water temperature drops below the optimum. It is
loss, ulcerations on the body, head and mouth, liver a common problem in hatcheries, affecting eggs and
pale, with small red spots and dark‐red spleen. Motile reducing hatch rates.
Aeromonas infections occur in freshwater. Poor water
quality, cold temperature and skin injury may facilitate 18.9.4 Parasite Infestations
infections. The mortality is typically chronic with low The protozoan parasite, Ichthyophthirius multifiliis (com-
daily losses. mon name, Ich), can cause severe mortalities in tilapias
and other freshwater fish (section 11.5.5). This parasite is
Other bacterial infections include vibriosis (due to most lethal at water temperatures between 20 °C and 23 °C,
Vibrio species), edwardsiellosis (due to Edwardsiella so it is not a problem when tilapias are farmed in their
tarda) and columnaris (due to Flavobacterium columnare). normal warm water temperatures. Other ciliated protozo-
Recently, a rickettsia‐like organism identified as Francisella ans that affect tilapias are Trichodina, Trichodinella,
species has also been associated with high tilapia mortali- Chilodonella, Apiosoma, Ambiphrya and Epistylis.
ties in Central America. Non‐specific clinical signs, such Common monogenetic trematodes such as Dactylogyrus
as erratic swimming, anorexia, anaemia, exophthalmia species and Gyrodactylus species, and parasitic crusta-
and high mortality are displayed. Infected fish have ceans such as Lernaea, Ergasilus and Argulus species, have
enlarged spleen and kidney that contain white nodules. been observed in tilapias. Tilapias grown in seawater are
The disease causes mortality of about 50%. Clinical signs highly susceptible to an ectoparasitic marine monogenean
of most bacterial infections in tilapias are quite similar, so flatworm, Neobenedenia melleni. Although most parasites
it is necessary to isolate, culture and identify the pathogen do not cause mortality, they predispose the fish to other
for diagnosis and treatment purposes. serious infections such as streptococcosis, because they
damage the scale, skin, fins or gills.
18.9.2 Viral Diseases
18.9.5 Disease Management
Lymphocystis and infectious pancreatic necrosis‐like Tilapias are among the hardiest of farmed fishes with
virus have been known to occur in tilapias, but neither respect to disease resistance, yet epizootics with eco-
poses a major disease threat. However, a newly emerging nomic implications do occur. Disease prevention is
viral disease—Tilapia Lake Virus Disease (TiLVD)—has always better than trying to treat an outbreak once it has
caused large losses of young fish in at least eight coun- started. Keys to reducing the incidence of diseases in tila-
tries on three continents and has become the most seri- pia culture include:
ous disease of farmed tilapias (OIE, 2018). ●● Maintain the best possible water quality;
●● Maintain prudent stocking densities and standing
Tilapia Lake Virus is a novel RNA virus in the family
Orthomyxoviridae. It was first reported in wild and crops;
farmed fish in Israel, and was named for the location ●● Use high‐quality feeds and control feeding;
(Kinneret Lake, or the Sea of Galilee) from which it was ●● Disinfect the water supply and equipment used in the
first isolated (Eyngor et al., 2014). Losses attributed to
TiLV have been documented in farmed Nile tilapia, culture facility;
hybrid Nile × blue tilapia, and wild Sarotherodon gali- ●● Remove dead and moribund fish quickly from the cul-
laeus, although host susceptibility may be wide within
the tilapias. The virus does not cause disease in humans. ture system;
●● Handle tilapias gently during stocking, sampling, etc.; and
The disease affects mainly young fish during the warm- ●● Use prophylaxis during and after handling to aid wound
est times of the year and losses can be very high (>90%)
in affected populations. The disease is highly communi- healing.
cable and easily spreads from fish to fish. Clinical signs Diseases are also better managed by understanding the
include ocular abnormalities (cloudiness in the eye and requirements of the disease agent. Tilapia hatcheries use
ruptured lenses), skin ulceration, loss of appetite and salt water at 5–10‰ to control ciliate protozoan para-
abnormal behavior (lethargy and loss of schooling behav- sites. Marine flatworm may be controlled by the use of
ior). There is no treatment and impacts must be man- low‐salinity water. Although this type of treatment is
aged through strict biocontrol measures on the farm, possible in a land‐based system, it is impossible or very
regional, and national levels to control the spread of the
disease from affected populations (OIE, 2018).
412 Aquaculture to the water. As with antibiotics, some of these therapeu-
tants may not be legal in some countries.
difficult for sea cages, which must be towed into low‐
salinity water, if this is feasible. So, a novel method of 18.10 Harvest, Processing
using tropical cleaner fish such as the cleaning goby and Marketing
(Gobisoma genie) and the neon goby (Gobisoma ocean-
ops) has been found effective in reducing the parasite Harvest size of tilapias varies from 150 g to more than
load in such conditions. 600 g, depending upon the market requirements. Some
markets, such as in the Philippines, prefer smaller size
18.9.6 Prophylaxis tilapias because the typical portion size is a whole fish
Considerable success has been achieved in vaccinating per person. So, a family of four or five members prefers
tilapias against Streptococcus spp. (Klesius et al., 2006). to buy four or five fish weighing a total of ~1 kg for a
The vaccine is prepared by culturing the infectious meal. Larger harvest sizes are required for filleting.
organisms, and by killing them in formalin. Researchers Tilapias have relatively low dressing yields: only 50–55%
have found that the most effective vaccine incorporates of the fish is available as dressed carcass and 25–30% as
not just the killed cells, but also the culture medium in fillets. So a tilapia weighing more than 500 g is required
which the infectious organisms are grown. This vaccine to produce a fillet weighing 100 g.
is called an extra‐cellular products (ECP) vaccine.
Seining is the most common method used to harvest
The most effective delivery of vaccine is by injection into tilapias from ponds. It is difficult, however, to harvest
muscle or the peritoneal cavity. Optimum body size for tilapias by seining alone because they tend to jump over
vaccinating tilapias is 1–5 g. However, their effectiveness the seine or escape underneath the seine. Partial or
and the effort needed to inject each fingerling have been complete draining of the ponds is required for a complete
questioned. An immersion bath in the vaccine is also used harvest. Tilapias reared in more intensive systems are
for primary vaccination. A booster delivery of the vaccine relatively easier to harvest because of the smaller size of
is provided via feed for 21–30 days following the bath. the system and the higher fish density.
Tilapias vaccinated in this manner are protected against
infections for 9–12 months, and typically have 85–95% Tilapias reared in ponds often develop an off‐flavour
lower mortality compared to unvaccinated tilapia. problem due to metabolites of bacteria and blue‐green
algae that thrive in nutrient‐rich ponds. This problem is
Bacterial diseases are usually treated using medicated solved by stopping feeding and flushing water through
feeds. Antibiotics that have been used include florfenicol, ponds 3–7 days ahead of harvest. Alternatively, the fish
oxytetracyline, Romet® (a potentiated sulphonamide con- could be harvested and stocked in tanks with a flow‐
taining Sulphadimethoxine and ormetoprim), erythro- through water supply.
mycin and amoxicillin. Not all of these drugs are legal to
use in feeds for fish used in human consumption in all Harvested tilapias may be sent directly to the market
countries. External parasites can be treated with chemi- or to a processor for further processing and packaging
cals, such as copper sulphate, formalin, chloramine‐T, (Figure 18.13). When market conditions dictate that the
potassium permanganate or hydrogen peroxide applied
(a) (b)
Figure 18.13 Tilapias sold in diverse markets: (a) at pond side in Bangladesh. (b) in a seafood counter in Europe. Source: Reproduced with
permission from Dr Kevin Fitzsimmons, 2017.
tilapias are sold alive, extreme care must be exercised in Tilapias 413
harvesting and transporting the fish. Typically, the fish
are transported in metal or plastic holding tanks with accepted by other nutritionists who point out that the
adequate aeration. Fish for further processing may also overall fat content of tilapias is low, and therefore only
be transported alive or in ice. Tilapias are processed in a fatty acid levels cannot be considered as the criteria to
number of different ways depending upon market compare with oily fishes such as salmon. More impor-
requirements. The whole fish may be cleaned and frozen tantly, recent studies showed that tilapias reared in semi‐
whole or frozen as fillets. However, fresh‐chilled prod- intensive systems have relatively higher levels of n‐3 fatty
ucts fetch higher prices than frozen products in most acids compared to the tilapias intensively reared in tanks
markets. For chilling, the fish may be gutted and fed with pellets (Karapanagiotidis et al., 2006).
deheaded before refrigerated packing, or converted into
fillets. Fresh‐chilled products have a shelf‐life of 10–15 18.11 Summary
days post slaughter.
●● The common name ‘tilapia’ refers to members of the
Market value of tilapias ranges widely. Although whole Cichlidae family in the genera Tilapia, Sarotherodon
tilapias in a local market in a developing country may and Oreochromis. Most farmed tilapias belong to the
cost less than USD 1/kg, the retail price of fresh whole genus Oreochromis, including O. niloticus (Nile tilapia),
tilapias in a developed country may exceed USD 10/kg. O. aureus (blue tilapia), O. mossambicus (Mozambique
This enormous range of prices provides opportunities tilapia) and various hybrids among these and other
for producers as well as processors to maximise their Oreochromis species. Tilapias are native to Africa,
returns by keeping their operations flexible, which, in including parts of the Middle East. They are tropical,
turn, is beneficial from an economic perspective. freshwater fish that do not survive below 10–15 °C.
Producers may serve the entire spectrum of the market
or target a specific market niche and optimise their ●● Global production of tilapias exceeded 5 million t/yr in
resources to meet the needs of the chosen niche. 2014: second only to the carps in production volume.
Major tilapia‐producing countries are China,
Comparative nutritive values for tilapias, salmon and Indonesia, Egypt, Bangladesh and the Philippines.
chicken breast (Table 18.12) show that tilapias have a
healthier fatty acid profile than chicken breast meat. ●● Tilapias have desirable flesh quality and have many
However, the nutritive value of tilapias for humans is positive attributes as a farmed fish. Tilapias are easy to
regarded as low by some nutritionists, based on data that breed in captivity, they tolerate crowding and poor
the fishes have low levels of n‐3 fatty acids and high lev- water quality, and are relatively resistant to infectious
els of n‐6 fatty acids. This assessment is not widely diseases. They grow quickly to market size in a wide
variety of aquaculture systems.
Table 18.12 Selected nutrients provided by 100‐g raw portions each of tilapia, farmed Atlantic salmon, and chicken
breast meat.
Nutrient Tilapia Farmed Atlantic Chicken breast
salmon meat
Energy (kcal) 96 208 263
Protein (g) 20.08 20.42 14.7
Total lipid (g) 1.70 13.42 15.75
Total saturated fatty acids (g) 0.77 3.05 3.26
Total monounsaturated fatty acids (g) 0.65 3.77 6.48
Polyunsaturated fatty acids (g)
0.21 0.9 3.2
1. Linoleic acid (n‐6) 0.043 0.167 0.14
2. Linolenic acid (n‐3) 0.003 0.06 0
3. Arachidonic acid (n‐6) 0.007 0.862 0
4. Eicosapentaenoic acid (n‐3) 0.113 1.104 0
5. Docosahexaenoic acid (n‐3) 50 55 41
Cholesterol (mg)
Source: Data from Nutrient Data Laboratory of the United States Department of Agriculture.
https://www.nal.usda.gov/fnic/usda‐nutrient‐data‐laboratory.
414 Aquaculture fishmeal, which is a significant advantage of tilapias
aquaculture.
●● Tilapias mature quickly (4–6 mo) and reproduce pro- ●● Tilapias are more tolerant of adverse water quality
lifically in ponds. Uncontrolled reproduction causes conditions and are less prone to diseases than most
stunted, slow‐growing populations. Solutions include other cultured fish. However, there has been a steady
laborious inspection and hand‐sorting to select only increase in the incidence and severity of diseases in
males for stocking, hybridisation between certain spe- intensive tilapia culture systems. Diseases can be
cies to produce all‐male populations, masculinising fry treated with antibiotics or therapeutants. Disease inci-
with synthetic androgens, and various types of genetic dence can be reduced by maintaining good culture
manipulation to produce either monosex or sterile conditions and using high‐quality feeds.
stocks. ●● Harvest size of tilapias varies from 150 g to more than
600 g, depending upon the market requirements.
●● Tilapias are opportunistic omnivores and grow well in Tilapias have relatively low dressing yields: only
fertilised ponds, either in monoculture or polyculture 50–55% of the fish is available as dressed carcass and
with other fish—particularly various Chinese and 25–30% as fillets. Harvested tilapias may be sent
Indian major carps. Production can be increased by directly to local markets or to a processor for further
supplemental feeding with various agricultural by‐ processing, packaging and transportation to domestic
products. The nutritional requirements of tilapias are or international markets.
well‐known and precisely formulated compound
feeds can be used for grow‐out in intensive systems.
High‐performance feeds can be formulated without
References Klesius, P. H., Evans, J. J., Shoemaker, C. A. et al. (2006).
Streptococcal vaccinology. In: Lim, C. and Webster,
Beardmore, J. A., Mari, G. C. and Lewis, R. I. (2001). C. D. (Eds) Tilapia: Biology, culture and nutrition.
Monosex male production in finfish as exemplified by Food Products Press, New York.
tilapia: applications, problems, and prospects.
Aquaculture, 197, 283–301. Lim, C. and Webster, C. D. (2006) Tilapia: Biology, Culture
and Nutrition. Food Products Press, New York.
Beveridge, M. C. M. and McAndrew, B. J. (2000). Tilapias:
Biology and Exploitation. Springer, Dordrecht. Lovell, T. (Ed) (1998). Nutrition and Feeding of Fish.
Springer, Dordrecht.
Bhujel, R. C. (2000). A review of strategies for the
management of Nile tilapia (Oreochromis niloticus) Moura, R. S. T., Valenti, W. C. and Henry‐Silva, G. G.
broodfish in seed production systems, especially hapa‐ (2016). Sustainability of Nile tilapia net‐cage culture in
based systems. Aquaculture, 181, 37–59. a reservoir in a semi‐arid region. Ecological Indicators,
66, 574–582.
Bhujel, R. C. (2014). A Manual of Tilapia Business
Management. CAB International, Wallingford. Ng, W‐K. and Romano, N. (2013). A review of the
nutrition and feeding management of farmed tilapia
Edwards, P., Lin, C. K. and Yakupitiyage, A. (2000). Semi‐ throughout the culture cycle. Reviews in Aquaculture,
intensive pond aquaculture. In: Beveridge, M. C. M. and 5, 220–254.
McAndrew, B. J. (Eds.) Tilapias: Biology and
Exploitation. Pp 377–403. Springer, Dordrecht. OIE (World Organisation for Animal Health). (2018).
Tilapia Lake Virus (TiLV)—A Novel Orthomyxo‐like
El‐Sayed, A‐F. M. (2006). Tilapia Culture. CAB International, Virus. OIE Technical Disease Card. Accessed 11
Wallingford. March 2018. http://www.oie.int/fileadmin/Home/
eng/Internationa_Standard_Setting/docs/pdf/A_
Eyngor, M., Zamostiano, R., Kembou Tsofack, J.E., TiLV_disease_card.pdf.
Berkowitz, A., Bercovier, H., Tinman, S., Lev, M.,
Hurvitz, A., Galeotti, M., Bacharach, E. and Eldar, Plumb, J. A. and Hanson, L. A. (2011). Health Maintenance
A. (2014). Identification of a novel RNA virus lethal and Principal Microbial Diseases of Cultured Fishes,
to tilapia. Journal of Clinical Microbiology, 52, 3rd edition. Wiley Blackwell, Ames.
4137–4146.
Suresh, A. V. and Lin, C. K. (1992). Tilapia culture in saline
Karapanagiotidis, I. T., Bell, M. V., Little, D. C. et al. (2006) waters: a review. Aquaculture, 106, 201–226.
Polyunsaturated fatty acid content of wild and farmed
tilapias in Thailand: Effect of aquaculture practices and Wang, M. and Lu, M. (2016). Tilapia polyculture: a global
implications for human nutrition. Journal of Agricultural review. Aquaculture Research, 47, 2363–2695.
and Food Chemistry, 54, 4304–4310.
415
19
Catfishes
Craig S. Tucker, Aaron A. McNevin, Les Torrans and Brian Bosworth
CHAPTER MENU 1 9.4 Clariid Catfishes, 431
1 9.1 Introduction, 415 19.5 Summary, 433
19.2 Pangasiid Catfishes, 415
19.3 Ictalurid Catfishes, 421 References, 434
19.1 Introduction blood of other fishes. Some of the smallest vertebrates
(<15 mm) are catfish, as well as some of the largest of
Catfishes are esteemed and popular food fish, with fishes (the giant Mekong catfish Pangasianodon gigas
important commercial and subsistence fisheries in can exceed 300 kg).
Europe, Asia, Africa, and North and South America. The
popularity of catfishes as food stimulated rapid develop- Species grown for food primarily come from five
ment of catfish aquaculture since 1980. Approximately f amilies: Pangasiidae (shark catfishes), Ictaluridae (North
4.5 million t of various catfishes were produced in 2014, American freshwater catfishes), Clariidae (air‐breathing
ranking catfishes third only to carps and tilapias as the catfishes), Bagridae (bagrid catfishes) and Siluridae
most commonly farmed fishes in the world.1 (sheatfishes). In addition to species grown for food,
dozens of freshwater species are treasured aquarium
The order Siluriformes (catfishes) is a wonderfully fish. This chapter focuses on catfishes that have been
diverse group of fish. The order has about 35 families studied most extensively for food fish aquaculture: the
and comprises 2500 to 3000 species, depending on con- pangasiids, ictalurids and clariids.
stantly changing systematics. About 10% of all fish spe-
cies are catfish and catfishes are found on every continent 19.2 Pangasiid Catfishes
except Antarctica. The common name derives from sen-
sory barbels around the mouth that bring to mind a cat’s The family Pangasiidae comprises 2–5 genera and
whiskers. Catfish lack true scales but the skin of some 20–30 species. Pangasiid catfishes are native to the Indian
species is covered with bony plates. The leading edges subcontinent, southern China and Southeast Asia through
of the pectoral fins (and usually the dorsal fin as well) the Indonesian archipelago to Borneo. Two species,
have defensive locking spines, which may be venomous. Pangasius bocourti and, especially, Pangasianodon hypoph-
Most species have an adipose fin. Catfishes are mostly thalmus, have quickly become globally important aquacul-
bottom‐feeding, river‐dwelling omnivores but the order ture species.
includes two families with marine members. Among the
more unique species, there are cave dwellers, air breath- Growth of pangasiid aquaculture has been spectacular,
ers, wood eaters and parasitic catfish that feed on the especially in Vietnam. In 2000, total Vietnamese pangasiid
production was 135 000 t. By 2014 production was more
1 All production data in this chapter were obtained from the 2016 than 1.1 million t. Most Vietnamese production is traded
FAO Fishery and Aquaculture Statistics FishStatJ database http:// internationally with little domestic consumption. The
www.fao.org/fishery/statistics/software/fishstatj/en fish is also grown in Indonesia (ca. 418 000 t in 2014),
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.
416 Aquaculture below about 15 °C. Tra have well‐developed gills and a
modified swim bladder that functions as an air‐breathing
Bangladesh (ca. 361 000 t), Cambodia (45 000 t), Thailand organ: traits important for survival under highly inten-
(ca. 24 000 t), Myanmar (ca. 18 000 t), Malaysia (12 000 t) sive pond culture conditions.
and other southern Asian countries for local consumption
and trade; global pangasiid production in 2014 exceeded Tra migrate upriver for spawning during seasons of
2 million t. This section summarises P. hypophthalmus high precipitation and flooding, but live downstream in
aquaculture in Vietnam, which dominates global catfish deeper riverine habitats for most of their life. Migration
production. Additional information is found in Dung distances in the Mekong River can be several hundred
et al. (2008), Phan et al. (2009), Bui et al. (2010), Nguyen kilometres. Tra are benthopelagic omnivores. Young fish
(2013) and Phu et al. (2015). eat insects, algae and zooplankton; larger tra prey on
19.2.1 Biology crustaceans and other fish. Tra reach sexual maturity at
The Vietnamese name for P. hypophthalmus is ‘Cá tra 2 or 3 years old. Mature fish can grow to 1.3 m and up to
nuôi’ and P. bocourti is ‘Cá ba sa’, but because ‘Cá’ is the 50 kg, with females reaching a larger size than males.
Vietnamese word for fish, the two species are referred to Wild populations are currently considered endangered
as ‘tra’ and ‘basa’. Both species are used in aquaculture, by the International Union for the Conservation of
but tra is the preferred species because it is a facultative Nature because of overfishing and river flow changes
air‐breather, is more fecund, has higher survival in the related to dams.
nursery phase, and grows faster than basa. Other names
for tra include striped catfish, swai and panga. 19.2.2 Aquaculture
Before 1995 tra farming was considered a small‐holder
Tra have a relatively small, depressed head and a long, livelihood but is now almost exclusively an intensive,
laterally‐compressed body (Figure 19.1). The dorsal fin is export‐oriented activity. Fish initially were grown in
conspicuous and far forward on the body, inspiring cages suspended in rivers or net pens (fenced enclo-
another common name, ‘shark catfishes.’ The anal fin is sures) that isolate a section of river (Figure 19.2). As
relatively long, and the adipose fin is small. They have farmers expanded and intensified production, farming
two pairs of barbels: one pair each above and below the increasingly relied on ponds, which now account for
mouth. Young tra have a black stripe along the lateral more than 95% of total tra production. The switch from
line and a long black second stripe below the lateral line. cages to pond‐based systems began in about 2001 and
Tra are native to the large river systems in Thailand was related to disease losses and slower growth of fish
and Vietnam. They have been introduced to Indonesia, in cages. These production instabilities were caused by
Haiti, the Dominican Republic, Malaysia, China, Brazil impaired water quality in the Mekong River. Impaired
and Bangladesh. Tra tolerate salinities from 0‰ to 15‰ water quality was partially self‐inflicted as rapid expan-
but salinities below 7‰ provide best growth. Best growth sion of cage and net pen culture caused locally high
occurs between 25–34 °C and pH 6.5 to 8.5. Tra will not loadings of organic matter, but degraded environmental
survive prolonged exposure to water temperatures quality was also related to water‐flow restrictions
caused by upstream dams.
Figure 19.1 Tra catfish (two left fish) and rohu carp in a market,
Can Tho City, Vietnam. Source: Reproduced with permission from Grow‐out ponds commonly are operated with high rates
Bill Daniels, 2017. of water exchange, 30 to 100% of pond volume exchanged
per day, which effectively makes them flow‐through sys-
tems rather than ponds. Pond‐based systems are variously
sized but all are operated at a high level of intensity.
19.2.2.1 Culture Cycle
The typical tra culture cycle begins with broodstock
procurement. Low fecundity during the cool season
(November to January) results in most hatcheries operat-
ing from February to October, and March through August
is the best time for reproduction. Broodfish are induced to
spawn, eggs are incubated in a hatchery and larvae are
transferred to enriched nursery ponds. Fry remain in the
nursery ponds for 2–3 mo, in either one or two stages.
After the nursery phase, fingerlings are moved to grow‐
out systems where they are fed for about 6 mo before
reaching market size of about 0.8–1.5 kg.
Catfishes 417
Figure 19.2 Cages used for tra farming in the Mekong River. Source: Reproduced with permission from Aaron McNevin, 2017.
19.2.2.2 Hatchery Practices conical hatching jars with up‐welling water to keep eggs
Tra aquaculture originally relied on wild‐caught juveniles suspended. Eggs hatch within 24 hr and the yolk sac is
to initiate the production cycle. Even after a ban on the absorbed in another 24 hr. Larvae are transferred to
catch of wild‐caught seed in 1994, the practice was com- nursery systems just before the yolk sac is fully absorbed.
mon until the late 1990s. With the development of inten-
sive grow‐out production systems, there has also been a 19.2.2.3 Fingerling Production
rapid growth in hatcheries and nurseries. The first tra Most tra production is not vertically integrated because
hatcheries were started by former operators of nurseries of the industry grew from an activity initially dominated by
wild‐caught seed. State‐owned hatcheries were then estab- small‐holders. Although some hatcheries have nursery
lished to maintain the genetic integrity of broodstock and facilities, most fry‐to‐fingerling culture is accomplished
to improve hatchery production, but the private sector is by separate operators. Most nursery operators use a
currently producing most of the seed for the industry. 1‐stage nursery from larvae to fingerlings, but some use
a 2‐stage system (larvae to fry and fry to fingerling).
Broodstock are typically developed from hatchery
stock and replaced every 2–4 yr. Broodfish weigh Earthen nursery ponds are 0.1–0.5 ha with an average
5–10 kg. Hatcheries begin producing fry after the water depth of 1.5–2.0 m. Ponds are prepared by drying,
November through January cool season. Spawning is liming, filling with water filtered through a mesh sock to
induced by a series of human chorionic gonadotropin exclude predators and adding live zooplankton as a food
(hCG) injections. On average, females receive 4–5 hCG for the young fish. Larvae are stocked at 500–800 m2.
injections over 3 days, increasing from about 500 to Water is usually not exchanged during the nursery phase
3000 IU/kg. Milt and eggs are stripped from broodfish because water exchange could introduce predators and
and mixed in large bowls. Fertilised eggs are incubated in wash out food items.
418 Aquaculture daily for fish greater than 800 g. Average annual produc-
tion is 300 to >800 t/ha, with a desired harvest weight of
Food is provided during the first weeks of culture by 0.8–1.5 kg/fish. The climate in Vietnam allows for
adding live zooplankton. Zooplankton are added to approximately 1.3 crops/yr.
ponds at 20–30 kg/ha, and nursery operators can buy
bulk lots of zooplankton from farmers who culture them, The extraordinary productivity of tra pond farming is
or they can collect them from ditches and canals in the attributable to the year‐round growing season, the use
surrounding areas. Formulated feeds are offered after of deep ponds with high water exchange rates, and the
about 2 weeks. Survival rates range from 10 to 30% over hardiness and air‐breathing ability of the fish which
this nursery phase. In the 2‐stage nursery process, fish allow intensive culture. Mechanical aeration is seldom
are thinned after about 30 days to a density of approxi- used in tra farming because the fish, being facultative
mately 200–300 fish/m2 and achieve a survival of about air‐breathers, are very tolerant of low dissolved oxygen
30%. Fingerlings are typically transferred by boat to concentrations and water exchange alone provides ade-
grow‐out operations when they reach 15–30 g. quate dissolved oxygen. Water exchange also removes
nitrogenous waste products and reduces or eliminates
19.2.2.4 Grow‐out algal‐related off‐flavours. Farmers often judge how
Since 2013, there has been an increasing trend of con- much water to exchange based on their feeding rate,
solidation in the tra grow‐out sector. Most fish are grown fish appetite, fish behaviour or water colour. Water
in intensive pond farming using formulated feeds and exchange rates increase as fish grow: daily water
high rates of water exchange. Production intensification exchange is infrequent during the first two months of
and consolidation is driven by the export market that farming and increases to 30–100% of pond volume per
requires a reliable and consistent supply of fish. Further, day near harvest. Water exchange is accomplished
traceability is becoming a mandate for market entry and using large electric, or more commonly, diesel‐powered
is more challenging for small‐holders to achieve because pumps (Figure 19.3).
they have less control over the supply chain.
Harvesting is done almost exclusively by hand with
Tra grow‐out ponds range from 0.5–1.2 ha and average seines (Figure 19.4). The entire fish crop is harvested at
4 m in depth. This is considerably deeper than most one time. Pond depth must be decreased by at least half
other aquaculture ponds. Deep ponds with high embank- to allow efficient harvest. After harvest, the remaining
ments reduce the risk of fish escape during floods and pond water is discharged into the environment.
the increased volume allows high stocking densities. Harvested fish are loaded onto boats by hand and
Fingerlings are added to grow‐out ponds at 45–75 fish/m2 transported to processing plants that are strategically
and feed is provided at 2–5% of body weight per day. located on river banks to decrease time from harvest to
Three feedings per day are provided for fish less than processing.
100 g, twice daily for fish between 100–800 g, and once
Figure 19.3 Pumping water from a river
into a distribution channel to supply water
to tra culture ponds. Source: Reproduced
with permission from Aaron McNevin,
2017.
Catfishes 419
Figure 19.4 Harvesting tra from a pond in
Vietnam. Source: Reproduced with
permission from Aaron McNevin, 2017.
19.2.3 Nutrition and Feeds Table 19.1 Typical composition of a feed used for tra
(Pangasianodon hypophthalmus) grow‐out.
Dietary requirements of tra are not as well‐known as for
other common aquaculture species. Dietary protein Ingredient Content
requirement for maximum growth ranges from 25–38%
depending on culture stage: fish from 5–50 g require Fishmeal (%) 12.0
34–38% protein in the diet; from 50–100 g, 32–34%; from Soybean meal (%) 22.5
100–300 g, 30–32%; 300–500 g, 28–30%; and fish over Wheat flour (%) 12.5
500 g require 24–26% protein (Glencross et al., 2011). Rice meal (%) 10.0
Rice bran (%) 22.0
Feeds for tra have changed as rapidly as the industry Cassava (%) 19.0
has grown. Prior to 2000, most producers used low‐qual- Fish oil (%)
ity feeds prepared on‐site from agricultural by‐products 2.0
and wild‐caught fish. The goal of using farm‐made feeds Source: Adapted from Nguyen, 2013.
is not to attain maximum nutrient utilisation efficiency
but rather to grow fish at a lower cost than possible when meal, blood meal, and meat and bone meal because of
purchasing feed from a trader or vendor. Although farm‐ fishmeal’s high cost. A typical feed formulation is
made feeds are still used in the industry, the proportion provided in Table 19.1.
of farms using manufactured pelleted feeds for grow‐out
is increasing yearly. This is a sign of the development of a 19.2.4 Infectious Diseases
more industrialised scale of tra farming. Intensification of tra farming has been accompanied by
an increase in the incidence and severity of infectious
During the 1990s most food fish producers prepared disease outbreaks. Bacterial diseases caused by
farm‐made feeds using trawl‐caught fish not directly Edwardsiella ictaluri, Flavobacterium columnare and
used for human consumption (trash fish) mixed with a Aeromonas spp. are the most common causes of fish loss.
variety of products such as eggs, soy, rice, blood, house- Losses are also caused by a variety of protozoal and
hold vegetables and vitamin premixes. These feeds pro- metazoan infections. Disease losses vary widely from
duced poor feed conversion ratios compared with fish farm to farm and seasonally. Every farm experiences dis-
grown on manufactured, pelleted feeds. Feed type also ease losses of some magnitude and cumulative losses
impacts pond effluent quality because of better nutrient during the grow‐out phase vary from 30–60%. High
retention when using manufactured feeds. incidence of infectious diseases and high mortality
rates have been associated with high stocking rates, poor
The main ingredients of tra pelleted feeds are fish-
meal, soybean meal, rice bran, blood meal and meat and
bone meal. The quantity of fishmeal used in feeds range
from 3–20%; feeds for smaller fish have higher fishmeal
levels. Many producers replace fishmeal with soybean
420 Aquaculture 19.2.4.3 Disease Treatments
The general approach to disease treatment in tra
quality of the water supply and the ease of pathogen aquaculture is the same as in most other types of
transfer among farms. Ease of pathogen transfer is facili- aquaculture, particularly in the early stages of
tated by the shared water supply, proximity of many indi- industry development: medicated feed therapy is
vidual ponds and farms, and the high water‐exchange used to treat bacterial diseases and water‐soluble
rates in ponds. chemicals, such as copper sulphate are used to treat
external parasites. A notable feature of Vietnamese
19.2.4.1 Bacterial Diseases aquaculture, however, is the extremely wide variety of
The bacterium Edwardsiella ictaluri causes bacillary antibiotics, disinfectants, parasiticides, and probiot-
necrosis of Pangasius (BNP), the most important disease ics that are used. For example, 28 antimicrobials were
of farmed tra. Infections may occur in all ages of tra, but authorised in 2012 for use in Vietnamese aquaculture,
highest mortalities are in fingerlings. Highest incidence which is far higher than most other countries. Also,
of BNP is during the cooler, rainy season. The disease is drugs and chemicals are often misused, primarily
caused by the same bacterium that causes enteric septi- because industry development has outpaced the
caemia of catfish (ESC) in channel catfish. Antibacterial availability of fish disease diagnostic services and
drugs added to feed are the most common treatment for many farmers lack the technical training required to
BNP, although misuse has caused widespread resistance diagnose diseases and make informed treatment
to several commonly used drugs. Vaccines have been choices. There are signs that the situation is
recently developed for use in treating BNP. improving, as larger‐scale producers increasingly
have staff with formal fish health training and farms
Motile aeromonad septicaemia (MAS) is caused by have formal health management plans. These
several bacterial species of the genus Aeromonas (most changes are occurring primarily in response to the
commonly A. hydrophila, A. sobria or A. caviae). The incentives associated with environmental certification
disease is also called red spot disease in tra and haemor- programs.
rhagic septicaemia in channel catfish. It is the second to
BNP as the most common bacterial disease of farmed One of the greatest challenges for an emerging food
tra. As with BNP, this infection is common at the begin- source is to develop and maintain a reputation as a safe,
ning of the wet season. Feed‐delivered antibiotics are the quality product. This has been hampered in Vietnam
most common treatment for MAS, although disease because of the use of chemicals and antibiotics that are
incidence and severity can be significantly reduced by not approved in many importing countries or are
simply reducing fish stocking density and maintaining banned in Vietnam. Due to lack of technical knowledge,
good water quality. small‐holder farmers are particularly likely to misuse
drugs and chemicals. Health management practices
19.2.4.2 Protozoan Parasites and the implications of drug and chemical misuse in tra
Parasitic infections collectively are second to BNP as the aquaculture are reviewed by Rico et al. (2012) and Phu
most commonly reported cause of disease in tra (Phan et al. (2015). In 2014, the Vietnam government banned
et al., 2009). Parasitic infections cause reduced growth, the use of 23 antibiotics and therapeutic chemicals in
predispose fish to bacterial diseases or kill fish. aquaculture.
External infections of gills or skin by ciliated protozo- 19.2.5 Processing
ans (Trichodina spp., Apiosoma spp., Epistylus spp., and
others) or by monogenetic trematodes (Thaparocleidus Tra are typically harvested at 0.8–1.5 kg/fish, which
spp., Dactylogyrus spp., Gyrodactylus spp., and others) yields two ~150–250 g fillets. There are few products
are extremely common but cause problems only when produced for export other than fillets. However, by‐
infestations are heavy. They may occur when fish are products from tra processing are used for various domes-
predisposed by crowded conditions or poor environ- tic foods, pastes, and meals. All filleting is done by hand
mental conditions. They are especially problematic in because fillet quality is better than when machinery is
the nursery phase. Incidence and severity of external used for skinning and filleting. Reliance on hand‐
parasite infestations is seasonal, with heavier infestations processing means that many jobs are created by the
during the rainy season or periods of cooler weather. processing sector. There is little differentiation between
External parasite infestations are treated with copper tra and basa at processing plants or in marketing, and
sulphate or formalin added to the water. both species are similarly processed (Figure 13.15),
packed, and sold as one product, pangasius.
A variety of microsporidean, myxosporidean, nema-
todes, digenetic trematode and other parasites are found
on or in tra. In most cases, these parasites cannot be
treated or are of unknown pathogenicity.
19.2.6 Future of Tra Aquaculture Catfishes 421
Tra aquaculture in Vietnam has moved from a largely
cage‐based, open‐water production system to earthen Mexico, the Russian Federation, Brazil, and Cuba. Hybrid
ponds with high water exchange rates. Problems associ- catfish accounted for less than 1% of United States catfish
ated with water exchange, such as pollutant discharge aquaculture in 2000 and less than 25% of in 2012, but con-
and lack of biosecurity, will be incentives to develop sys- tributed more than 50% in 2015. Few hybrid catfish are
tems with less reliance on water exchange to maintain currently produced outside the USA.
good farming conditions. Diseases are a major concern
for the sustainability and profitability of the Tra catfish Essentially all channel and hybrid catfish grown in the
farming sector in Vietnam; and maintaining the current USA are produced in ponds and consumed domestically.
farming intensity and reliance on high water exchange Many (perhaps half ) of China’s channel catfish are grown
will likely result in the spread of more disease that may in cages or pens placed in large reservoirs or rivers, and a
have a dramatic effect on production. Increased disease variable but significant proportion of Chinese produc-
incidence may also have indirect effects on markets tion is exported, primarily to the USA. In 2008, almost
related to illegal or inappropriate use of therapeutic 10% of Chinese production was exported, but exports
drugs and chemicals. Consolidation of the industry may fell to less than 2% in 2012. Information is scarce on
assist in the drive for more responsible practices because farming techniques for channel catfish grown in China
there is a greater investment at stake. or elsewhere, so this chapter will focus on ictalurid aqua-
culture practices in the USA.
A further challenge as the Tra industry matures is the
reputation of the species as being an inexpensive ‘white- 19.3.1 Biology
fish’ alternative. Although this reputation has aided in Channel catfish are native to rivers draining to the Gulf
initial market development in European nations, the of Mexico in the USA, Mexico, and Central America; and
Vietnamese seek to sell products with an enhanced north to the Great Lakes and Hudson Bay drainages. It is
image and higher price that are produced with greater a popular sport fish and has been introduced throughout
traceability and adherence to sustainable production North America and elsewhere.
practices. Certification programs have helped the indus-
try in this regard and a commitment by the Vietnamese Channel catfish have moderately depressed heads and
government to have a large portion of the industry certi- rounded to laterally compressed bodies. They are white
fied has helped maintain market share. Of course, certi- on the undersides, shading to greyish blue or olivaceous
fication comes with added expenses of standard adoption to nearly black dorsally. Young fish have irregular dark
and auditing fees, and it remains to be seen if the effort to spots on their sides. Eight barbels, four dorsal and four
shift the reputation of tra to a more responsibly pro- ventral, are located around a sub terminal mouth.
duced fish will bring with it greater economic returns. Pectoral and dorsal fins contain sharp spines. The anal
fin is short, rounded, and contains 24–30 rays.
19.3 Ictalurid Catfishes
Channel catfish thrive in a variety of habitats: from
The exclusively North American family Ictaluridae com- clear, swiftly flowing streams to sluggish rivers, lakes and
prises seven genera with at least 45 species. Many are ponds. They are bottom‐dwelling opportunistic omni-
fine food fish and important in local capture and recrea- vores. Young fish feed primarily on detritus, aquatic
tional fisheries. Channel catfish (Ictalurus punctatus), insects and zooplankton; adults feed primarily on aquatic
blue catfish (I. furcatus) and their interspecific hybrid are insects, freshwater crayfish and small fish. Age at sexual
important in aquaculture. maturity varies from 2–12 yr, depending on fish strain
and the length of the growing season (fish generally
Prior to 2000, nearly all ictalurid aquaculture took place mature faster in warmer climates). In nature, 2–4 yr may
in the USA and channel catfish was the only species be required to reach a weight of 0.5 kg, although growth
farmed. Since that time, channel catfish aquaculture rate depends on temperature and food availability.
developed rapidly in China and the hybrid channel × blue Channel catfish may live for over 20 yr and attain weights
catfish accounts for an increasing proportion of United in excess of 20 kg.
States production. In 2014, ~394 000 t of ictalurid catfish
were produced globally, with China producing ~249 000 t. Channel catfish evolved in a temperate climate and are
United States ictalurid aquaculture peaked in 2003 at adapted to grow and survive over a wide temperature
slightly greater than 300 000 t but decreased to ~139 500 t range. Optimum water temperature for growth is
in 2014. Minor amounts of channel catfish are grown in 25–30 °C, but fish can survive at temperatures from just
above freezing to ~40 °C. Growth is slow at temperatures
less than 15 °C and feeding activity essentially stops at
temperatures below ~10 °C. Salinity tolerance varies with
life stage. Eggs tolerate salinities as high as 16‰ but tol-
erance decreases to 8‰ at hatching and then increases to
422 Aquaculture of maturity (> 5 yr) of blue catfish females make produc-
tion of the reciprocal hybrid less efficient.
an upper salinity tolerance for adults of ~12‰. Growth
of adults is slowed at salinities above ~6‰. Environmental requirements of hybrid catfish are sim-
ilar to those of channel and blue catfish, but hybrids are
The blue catfish is a close relative of channel catfish slightly more tolerant of low dissolved oxygen than chan-
and has potential for exploitation as a farmed species in nel catfish. Hybrids are superior to blue catfish but simi-
its own right. But the main interest in blue catfish stems lar to channel catfish in tolerating handling during
from its contribution to the genotype of hybrids with harvest and transport. Hybrids feed better at cooler
channel catfish. The native range of blue catfish is similar water temperatures than either parent species.
to that of channel catfish, although blue catfish were not
native to rivers draining north into the Great Lakes and 19.3.2 Aquaculture
Hudson Bay. Blue catfish resemble channel catfish, but Taken as a whole, channel catfish possess a combination
adults have a smaller head and a longer, less‐rounded of biological and cultural attributes that make them excel-
anal fin with 30–36 rays. Blue catfish are sexually mature lent fish for large‐scale aquaculture in warm‐temperate
at an older age and larger size than channel catfish. For climates. Channel catfish rarely reproduce in culture
practical purposes, however, channel and blue catfish ponds (owing to the absence of nesting sites), so the farmer
have similar habitat and environmental requirements. has control over pond populations. But they are easy to
spawn under proper conditions and large numbers of fry
Hybrids between channel and blue catfish can be made are readily obtained using simple hatchery methods. Fry
using either species as the maternal or paternal parent. are relatively large and accept manufactured feeds at first
However, the F1 hybrid between the ♀ channel catfish feeding; fish do not require special food at any life stage.
and ♂ blue catfish is used nearly exclusively for commer- Channel catfish are hardy, tolerate a wide range of tem-
cial aquaculture (unless otherwise noted, ‘hybrid catfish’ peratures and environmental conditions, and adapt well to
will hereafter refer to the F1 ♀ channel catfish × ♂ blue all commonly used culture systems, although essentially
catfish). Colouration, fin ray counts, and caudal and anal all channel and hybrid catfish produced in the USA are
fin shape are intermediate to parent species. Compared grown in earthen ponds (Figure 19.5).
to hybrids from mating ♀ channel catfish and ♂ blue cat-
fish, hybrids from the reciprocal cross have slower
growth and are more similar to the blue catfish in appear-
ance. In addition, the large size (> 4 kg) and advanced age
Figure 19.5 Channel catfish farm in northwest Mississippi, USA. Source: Reproduced with permission from Danny Oberle, 2017.
Hybrid catfish are increasingly popular because of their Catfishes 423
consistently better growth, survival, and meat yield rela-
tive to channel catfish. Hybrids grow about 20% faster, Brood fish are maintained at relatively low standing
have 10–30% higher survival during both fingerling and crops (less than 2500 kg fish/ha) to provide good
grow‐out phases of production, and have 1–2% higher environmental conditions: overcrowding suppresses
meat yield. Physiological feed conversion efficiency is spawning. Brood fish are inspected every year or two,
about the same as channel catfish but ‘on‐farm’ feed con- and large fish are culled and replaced with smaller,
version is better because of the hybrid’s disease resistance younger brood fish. Female channel catfish spawn once a
and higher survival. The main disadvantages of the hybrid year, but males can spawn two or more times. Therefore,
are the increased cost and labour associated with produc- stocking more females than males makes more efficient
ing fry and difficulties in size‐grading fish during harvest. use of pond space. A good sex ratio in brood ponds is two
males for every three females.
The remainder of this chapter focuses on production
practices used in channel and hybrid catfish farming in Brood fish nutrition is important because a poor diet
the United States. Additional information is provided by may result in poor egg quality or reduced spawning suc-
Tucker and Hargreaves (2004). cess. Fish are fed a nutritionally‐complete manufactured
feed daily when water temperatures are above 15 °C.
19.3.2.1 Production Cycle Some producers stock forage fish into brood ponds to
Channel and hybrid catfish farming is conducted in five provide food in addition to manufactured feeds.
phases:
1) Broodfish spawn in the spring when water tempera- Channel catfish reproduction is controlled by seasonal
changes in water temperature. Cool water (less than
tures increase above 20 °C. ~15 °C) for 1 month or more stimulates gametogenesis.
2) Fertilised eggs are incubated in hatcheries until they A slow rise in water temperature to 20–25 °C initiates
spawning in the spring. Water temperatures of around
hatch, and fry remain in the hatchery for a week or 25–28 °C are considered optimum for spawning.
more.
3) Fry are transferred to a nursery pond and fed daily Channel catfish are provided with an enclosed nesting
through the summer and autumn. site for spawning. Containers are placed in the brood
4) Fingerlings are harvested in late autumn or winter pond shortly before water temperature is expected to
and transferred to grow‐out ponds. rise into the range for spawning. Spawning occurs over a
5) Fish are harvested when they reach a size desired for period of several hours as several layers of adhesive eggs
processing (0.5–1.0 kg). are deposited. Females of 2–5 kg typically lay between
In the catfish‐producing areas of the south‐eastern USA, 6500–9000 eggs/ kg body weight. Once spawning is com-
where water temperatures are below 20 °C for about plete, the male chases the female from the nest and
5 mo of the year, 15–18 mo are required to produce a guards the egg mass. Nesting containers are checked
market‐size catfish from an egg. every 2 or 3 days for eggs (Figure 19.6). Eggs are ~4.5 mm
Events described above imply that a clearly defined in diameter and are initially light yellow, becoming
production cycle exists which, like terrestrial crops, is brownish yellow with age. Spawning success (percentage
determined by seasonal water temperature variation. of females spawning) ranges from 40–80% each year
Although seasonal changes in water temperature regulate and depends mainly on the condition and age of the
fish reproduction and growth, market demands are such female brood fish and water temperatures during
that there is no well‐defined schedule for producing the spawning season.
market‐sized fish. Broodfish spawn and fry are produced
in spring, but fingerlings are stocked into grow‐out Methods used in fry production are the main differ-
ponds throughout the cooler months of the year and ence between the channel catfish and hybrid catfish
marketable fish are harvested year‐around to meet the production. Pond spawning to produce channel catfish
needs of processing plants. On most farms, ponds con- fry is efficient, simple, and economical. Although hybrid
tain fish of various sizes throughout the year. catfish fry can be produced by placing female channel
catfish and male blue catfish in ponds and allowing them
19.3.2.2 Reproduction to spawn, the percentage of females that spawn is low
Although channel catfish may mature sexually at 2 yr, and fry production is too inconsistent to meet the needs
when weighing as little as 0.3 kg, they must be at least 3 for commercial farming. Commercial hybrid catfish fry
years old and weigh at least 1.5 kg for reliable spawning. production is based on hormone‐induced ovulation of
Fish 4–6 years old, weighing between 2 kg and 4 kg, are channel catfish females, manual ‘stripping’ of eggs and
considered prime spawners. fertilisation of eggs with sperm from blue catfish males.
Female channel catfish are removed from brood ponds
when water temperatures are conducive to natural
spawning. Females are selected based on external
characteristics indicating the female is ‘ripe’ and near
424 Aquaculture
Figure 19.7 Channel catfish sac fry ~ 2 days post‐hatch. Source:
Reproduced with permission from Les Torrans, 2017.
Figure 19.6 Channel catfish egg mass taken from a container
used as an artificial nesting site. Source: Reproduced with
permission from Les Torrans, 2017.
ovulation. Blue catfish males are held in ponds separate Figure 19.8 Channel catfish swim‐up fry ~ 7 days post‐hatch.
from the channel catfish females. Males are removed Source: Reproduced with permission from Les Torrans, 2017.
from the pond, euthanised and the testes are removed
and macerated. Sperm is suspended and stored in a p rovided by surface agitators or by air or oxygen bub-
physiological saline solution and can be held at tempera- bled through air stones.
tures of 2–5 °C for 2–3 days. Sperm from one male is
used to fertilise eggs from 8 to 10 females. Sac fry are initially reddish‐gold (and thus called ‘red
fry’ by some farmers; Figure 19.7). Over a 3‐ to 5‐day
Females are held in oxygenated, flow‐through r aceways period after hatching, they absorb the yolk sac and turn
at 25–28oC during hormone induction and ovulation. black. At that time, fry (now called swim‐up fry or ‘black
Females are induced to ovulate with either luteinising fry’, Figure 19.8) swim to the water surface seeking food.
hormone‐releasing hormone analogue (LHRHa) or pitu- Swim‐up fry are fed 6–12 times per day for good survival
itary extract (carp or catfish). Hormone injection sched- and growth. Fry feeds are generally dry, finely ground,
ules vary, but usually involve a two‐injection protocol: a nutritionally complete feeds containing at least 50%
low concentration ‘priming’ dose the first day, followed crude protein. Fry are fed in the hatchery for 2–10 days
by a higher concentration ‘resolving’ dose the second before they are transferred to a nursery pond.
day, after which females ovulate within 24–48 hr.
Ovulating females are anaesthetised, and eggs are manu- Fertilised hybrid catfish eggs are either allowed to
ally stripped into a plastic container. Sperm are then adhere in a gelatinous mass and hatched in a similar way
added to the eggs, followed by addition of water to acti- to channel catfish egg masses or are prevented from
vate sperm and fertilise the eggs. sticking by addition of Fuller’s earth and hatched in large
‘hatching jars’ that resemble the McDonald jars used in
19.3.2.3 Hatchery Practices trout hatcheries. Major differences between hybrid and
Channel catfish hatcheries are simple facilities that use
single‐pass, flow‐through tanks for egg incubation and
fry rearing. Water temperature is 25–28 °C for best
results. Eggs hatch in 5–8 days depending upon water
temperature. At hatching, the fry (called sac fry at this
point) fall or swim through the wire‐mesh basket and
school in the corners of the tank. Sac fry are easily
siphoned into a bucket and transferred to a fry rearing
tank. Aeration in hatching and rearing tanks is
channel catfish hatcheries are the increased space and Catfishes 425
water‐flow requirements associated with holding chan-
nel catfish females for ovulation and the lower percent- 19.3.2.5 Grow‐out
age hatch of hybrid eggs. Percentage hatch for hybrid In contrast with cultural practices used in hatcheries and
eggs is about half that for channel catfish eggs, so roughly nursery ponds, which are relatively standardised across
twice as much water flow is needed. the industry, management of grow‐out ponds varies
greatly from farm to farm. In the early years of the catfish
19.3.2.4 Nursery Pond Management industry, before 1980, most farmers used some variation
After a brief stay in a hatchery, fry are stocked in nursery of the ‘single‐batch’ cropping system, in which only one
ponds at 200 000–400 000 fry/ha. Nursery ponds are ini- year‐class of fish is present in the pond at a given time.
tially fertilised to provide abundant natural foods because Fingerlings were stocked, grown to market size (usually
fry are difficult to feed the first several weeks after stock- 0.4–0.8 kg) and then completely harvested before the
ing. Fry begin accepting manufactured feed 2–3 weeks pond was restocked with new fingerlings to initiate the
after stocking. Fish are initially fed a finely ground, high‐ next cropping cycle. Fish were either harvested at one
protein feed (40–50% crude protein); feed particle size is time or harvested in two to four separate harvest events
increased as fish grow, and feed protein level is decreased. spaced over several months. After as much of the crop as
possible had been harvested by seining, the pond was
The same nursery pond protocols are generally used either drained and refilled, or restocked without draining
for hybrid catfish fry. However, due to the hybrid’s better to conserve water and decrease lost production time
survival and faster growth, some farmers harvest about between crops.
half the fingerlings in late midsummer and move them to
another pond. The process of splitting fingerling popula- After 1980, the catfish industry was expanding past the
tions reduces biomass density and allows faster finger- point where sales were primarily to local markets, and a
ling growth. new system, called multiple‐batch cropping, was developed
to provide a year‐round supply of market‐sized fish to
Fingerlings 5–9 months‐old are harvested from nurs- meet the demand of new regional and national markets.
ery ponds in the autumn, winter, and early spring for In the multiple‐batch system, a single cohort of finger-
transfer to grow‐out ponds. Channel catfish fry survival lings initially is stocked. The faster‐growing individuals
to the fingerling stage exceeding 75% is considered very are selectively harvested using a large‐mesh seine and
good. Hybrid fingerling survival is better, and often fingerlings are added to replace fish that are harvested or
exceeds 90%. Hybrid fingerlings are usually graded by lost to predators and diseases. The process of size‐
size before stocking in grow‐out ponds; channel catfish selective harvest and understocking continues for years
fingerlings are not usually graded. After all fingerlings without draining the pond. After a few cycles of harvest
have been harvested, the nursery pond is drained and and understocking, the pond contains a continuum
allowed to dry. of fish sizes ranging from recently stocked fingerlings
(20–40 g) to fish over 1 kg (Figure 19.9).
Figure 19.9 Channel catfish of mixed sizes
harvested from a pond under the
multiple‐batch cropping system. Note the
range of fish sizes, from ~ 0.4 to 1 kg/fish.
Source: Reproduced with permission from
Craig Tucker, 2017.
426 Aquaculture much aeration as conventional ponds or 2) split ponds.
Split ponds (Figure 19.10) are constructed by dividing an
The single‐batch cropping system is still used by some existing catfish pond into two unequal basins separated
farmers and remains common in areas where watershed by an earthen levee. Fish are confined in the smaller
ponds are used. Some watershed ponds are too deep to basin (usually about 15–20% of total water area) while
allow harvest without draining the pond, making it nec- the larger basin serves as a waste‐treatment lagoon.
essary to raise single crops of fish interrupted by pond A high‐volume pump circulates water between the
drawdown and draining. Single‐batch cropping is also lagoon and fish‐holding basin during daylight and aera-
used as the final stage of a 3‐phase production system tors maintain adequate dissolved oxygen in the fish‐
wherein fingerlings are grown to ‘stockers’ weighing holding basin at night (Tucker et al., 2014). Fish densities
100–200 g/fish in the second year, and stockers are grown of 25 000 to 35 000 fish/ha are used in intensive pond
to market‐sized fish in the third year. The single‐batch systems.
system is also commonly used when growing hybrid cat-
fish, which are more difficult to size‐grade at harvest Despite considerable variation in fundamental pro-
than channel catfish. duction variables, daily management of grow‐out ponds
is similar from farm to farm. When water temperatures
The other important management decision that farm- are above ~15 °C, fish are offered an extruded floating
ers must make, besides choice of cropping system, is fish feed of 26–32% crude protein. Feed is dispensed from
stocking density. There is no consensus on the best stock- mechanical feeders that are mounted on, or pulled by,
ing density, and this is evident from the wide range of vehicles. Usual practice is to feed fish once daily to near
stocking densities used in the industry, which varies from satiation based on visual assessment of fish feeding activ-
fewer than 10 000 fish/ha to more than 25 000 fish/ha. ity. Daily feed allowances in traditional grow‐out ponds
average 75–125 kg feed/ha during the late spring to early
Since 2010 many farmers have dramatically intensified summer period of maximum feeding activity and
production by using hybrid catfish and more intensive between 200–300 kg/ha, or more, in intensive pond sys-
pond‐based production systems. The new systems pro- tems. Feeding activity declines as water temperatures
vide the best environment to exploit the genetic poten-
tial of the hybrid catfish. Two types of intensive systems
are used: 1) smaller ponds (1–2 ha) with 2–3 times as
Figure 19.10 A split pond used for hybrid channel × blue catfish production. Water circulates between a 0.4‐ha fish‐holding basin and
a 1.4‐ha waste‐treatment lagoon through two open channels. A large, slow‐turning paddlewheel in the right‐hand channel pumps
water from the fish basin at the bottom of the photo into the lagoon. Water returns to the fish basin through the channel on the left.
Two 7.5‐kW paddlewheel aerators in the fish basin provide supplemental dissolved oxygen. Source: Reproduced with permission from
Danny Oberle, 2017.
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