527
23
Freshwater Decapod Crustaceans
Chaoshu Zeng, John S. Lucas and Paul C. Southgate
CHAPTER MENU 23.5 Freshwater Prawns, 543
23.1 Introduction, 527 23.6 Summary, 547
23.2 Farmed Species, 529 References, 548
23.3 The Chinese Mitten Crab, 530
23.4 Freshwater Crayfish, 536
23.1 Introduction body plan, e.g., in marine and freshwater shrimps the
abdomen is well‐developed (Figure 22.3) while in crabs
23.1.1 Morphology the abdomen in reduced to a flap which remains flexed
The crustacean order Decapoda is characterised by under the body (Figure 23.1).
h aving five pairs of legs, as its name describes. The pairs
of legs of a decapod often vary in form and function from 23.1.2 Habitats
anterior to posterior, with the anterior legs typically Some decapods are terrestrial, except during reproduc
being more involved in feeding. Often one or more tion when they move into the sea to release the larvae
pairs of legs have chelae: pincer‐like structures at the from their eggs, e.g., land hermit crabs and other land
appendage tip that are formed by the terminal segment crabs. The vast majority are aquatic: inhabiting environ
articulating with a projecting ‘finger’ from the second ments from wet soil near stagnant pools, to the intertidal
last segment (Figure 23.1). These anterior chelipeds zone to the abyssal depths of the ocean. They occur in
(legs with chelae) are enlarged in many species, with one salinities from freshwater to hypersaline conditions and,
of the pair being larger than the other. They may also be while having defined salinity ranges, many brackish
larger in males than females and of a different shape. water and coastal species are distinctly euryhaline
Large chelipeds may be used in crushing robust prey (tolerating a wide range of salinity).
such as bivalves, e.g., feeding by portunid crabs such as
the mud crab (Figure 23.1), or in aggression and display 23.1.3 Life Cycles
by males, e.g., Macrobrachium rosenbergii (section 23.5). As described in section 6.4.2, decapod crustaceans grow
Where the anterior legs are highly specialised for feeding in a staircase‐like fashion with smaller and more fre
or display, it is left to the posterior legs to carry the role quent ‘stairs’ at the beginning of growth. The concept of
of locomotion. These walking legs may also be special growth is confusing in that the period of no external
ised, e.g., in swimming crabs the last pair of legs is growth, when the exoskeleton (shell) is hard, the period
specialised as paddles and the crabs swim laterally between moults, is the period when the animal is feeding
when moving rapidly. In other cases, the legs are adapted and laying down tissue. Moulting or ecdysis, when the
for digging into the substrate, as in shrimps. enclosing exoskeleton is shed, and the animal abruptly
expands in size is not a period of tissue growth: the ani
The regular number of paired legs reflects the con mal’s body and appendages are soft and not functioning
servative body plan of decapods. They have a set number normally. Immediately after moulting, the protein tissue
of body segments and associated appendages (Table 23.1).
There is, however, great adaptive variation based on this
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.
528 Aquaculture
Figure 23.1 A mature male specimen of
the mud crab, Scylla serrata, showing its
first pain of legs adapted as huge chelae,
with the larger right‐hand one especially
enlarged for crushing. The next three pairs
of legs are for walking. The fifth pair of
legs, paddle‐like and adapted for
swimming, are obscured except for part of
the left one adjacent to the man’s hand.
The abdomen is much reduced and
evident as a small triangular flap. Source:
Venglois 2012. Reproduced under the
terms of the Creative Commons
Attribution Share Alike license,
CC‐BY‐SA 3.0.
content of the body is relatively low, and the fluid content moulting takes longer and the animal spends longer in a
is high. Large decapods that are harvested commercially phase when it is vulnerable to predation through poor
may be known as ‘empty’ during this period, because of mobility and defence. Some large decapods seek conceal
their relatively low meat content. The high fluid content ment during the period of moulting.
is because the body’s expansion is by rapid intake of fluid,
often by drinking. Fluid intake not only provides the As in most other arthropods, the presence of an all‐
mechanism for expansion of the body after moulting, it enclosing exoskeleton has another profound morpho
also provides force during moulting to split the old exo logical effect: there are no cilia, flagella, or similar
skeleton along pre‐determined lines and push the body organelles on the surface of the skin beneath the exoskel
out of the old exoskeleton through the splits (Figure 6.8) eton. This absence extends to the gametes, which have
no flagellum, and are thus non‐motile. The male crusta
This pattern of growth occurs even in the earliest larval cean must pass sperm to the female in packed masses,
instars, but the process of moulting during larval stages is known as spermatophores, during copulation. This is
very rapid and there is hardly any disruption to feeding. sometimes accomplished while the female is soft,
As the decapod grows larger, the period of moulting and immediately after moulting, and the copulating male
recovering a strong exoskeleton (calcification) after may push the spermatophores into the female’s
Table 23.1 Generalised morphology of decapods crustaceans.
Body region Body segments Appendages Typical functions
Head, enclosed by carapace
Thorax, enclosed by 1–2 antennae sensory
carapace 3–5 mandibles, maxillae mastication of food
6–8 maxillipeds collection and mastication of food
Abdomen
9–13 legs (often some locomotion, collecting food, display,
are chelated) aggression
14–18 pleopods swimming, brooding eggs (females),
spermatophore transfer (males)
19 uropods making a tail fan with telson for rapid
backward locomotion with abdomen flexing
Telson
Freshwater Decapod Crustaceans 529
reproductive system via her genital apertures to be Production (Thousand t) 5000
stored in her seminal receptacles. An alternative way 4000
of copulating with hard intermoult females is for the 3000
copulating male to put a sticky spermatophore mass 2000
on the female’s exoskeleton near her genital apertures, 1000
e.g., in freshwater crayfish (section 23.4). In shrimps,
the alternative ways of copulation with soft or hard 0
exoskeleton females are demonstrated in different
s pecies (section 22.5). Marine shrimp
FFrreesshhwwaattMeiertrtceprrnaaycfriwasnbhs
Like many crustaceans, the larvae of marine decapods
are typically members of the zooplankton. The earliest Marine crabs
larval instar of crustaceans is the nauplius, which hatches
from the egg. It has only three pairs of appendages, which Figure 23.2 Aquaculture production of the four main groups of
correspond to antenna 1 and 2, and mandible append decapod crustaceans in 2014. Source: Data from FAO 2015.
ages of the adult decapod. The larva then goes through a Reproduced with permission from John Lucas.
series of moults and instars or stages, adding posterior
segments and appendages, and modifying its append While shrimps have the greatest number of farmed spe
ages to suit the needs of the particular larval instars, until cies and the greatest annual production (although global
it reaches the adult number of body segments. This is the production in recent years is dominated by the whiteleg
pattern of development in shrimps (section 22.5). It is shrimp, Litopenaeus vannamei) (section 22.2.1); the sec
atypical, however, of other decapods. Most other deca ond in global aquaculture production is from a single
pod crustaceans suppress the nauplius stages as a part species of freshwater crab, the Chinese mitten crab,
of embryonic development within the egg. The larva Eriocheir sinensis. Freshwater crayfish are next in impor
that emerges has the adult or near adult number of tance and mainly from one species, Procambarus clarkii,
segments, although its form is often entirely different to the red swamp crawfish. Two species of freshwater
the juvenile and adult (Figure 6.6). In some species, vir prawn, Macrobrachium rosenbergii and M. nipponense,
tually the whole of larval development is suppressed and are next in importance (Figure 23.2).
developed within the egg and near‐juveniles emerge
from the egg at hatching. Apart from the freshwater mitten crab, there is also
production from brackish water and marine crabs
Environment is clearly important for early develop (Figure 23.2). They are from swimmer crabs of the
ment of decapod crustaceans in freshwater. One group, family Portunidae, mainly the mud crabs, Scylla
the freshwater crayfish remain in this environment s pecies (Figure 23.1), and the swimming crab, Portunus
throughout their life cycle and have no free living trituberculatus. They are farmed in a number of Asian
p lanktonic larval instars (section 23.4.3). On the other countries, often by on‐growing captured postlarvae or
hand, the mitten crab and the giant freshwater prawn juveniles for the former species, but using hatchery
have planktonic larval instars, and the sexually mature produced juveniles for the latter species. Particular
individuals move downstream, often through long p roblems with these portunid crabs are their aggressive
d istances, to release their larvae into brackish water. and cannibalistic behaviours, which limit the density
of culture.
23.2 Farmed Species
Not unexpectedly, China dominates the global pro
FAO (2014)1 lists 45 decapod species that are currently duction of decapod crustaceans, with almost 40% of
or have been farmed: shrimp production, all mitten crab production, and a
●● seventeen species of shrimps; high proportion of Macrobrachium species and fresh
●● eight crab species including one freshwater species; water crayfish production. Macrobrachium rosenbergii
●● seven species of freshwater crayfish/crawfish;
●● four species of giant freshwater prawns; and
●● three species of spiny and squat lobsters;
1 http://www.fao.org/fishery/statistics/global‐aquaculture‐
production/query/en
530 Aquaculture in the form of the transitional post‐larval megalopae,
between the final zoeal instar and the first juvenile
is not native to China but an introduced species for crab stage (section 23.3.2; Figure 6.6). This was an impor
aquaculture. Its production boomed during the 1990s tant breakthrough that enabled hatcheries to be estab
due to the widespread diseases of shrimps in China dur lished inland. However, it took time for the new
ing this period. However, the production of the native techniques to be adopted and improved, and it was only
species, M. nipponense, has caught up and considerably after 1990 that the Chinese mitten crab farming industry
exceeded the former species in recent years. Similarly, began to develop rapidly and spread far beyond its
the red swamp crawfish, native to southern USA and natural distribution range (Cheng et al., 2008).
Mexico, was introduced to China and this country has
become the dominant producer (>90%) of freshwater 23.3.1 Production Status
crawfish through this species. The USA state of Louisiana Chinese mitten crab farming now occurs in all provinces
is particularly noted for its production and special meals and regions of mainland China except the tropical Hainan
of red swamp crawfish, and was traditionally the largest province. It has also been farmed in Taiwan in recent
global producer, but this is no longer the case. years. The most important provinces for the farmed pro
duction of mitten crabs are Jiangsu and Hubei provinces.
23.3 The Chinese Mitten Crab Annual farming production has reportedly reached
823 259 t in 2015, which is a 56‐fold increase on produc
The Chinese mitten crab, Eriocheir sinensis, earned its tion in 1991 (Figure 23.4) (China Fisheries Statistical
name from the distinguishing feature of dense patches Yearbook 2016). Based on statistics from the China
of hairs on its chelipeds (Figure 23.3). The freshwater Fisheries Bureau, in 2001 hatchery production of Chinese
crab species is native to China and is distributed widely mitten crab seed (megalopae) exceeded 200 000 kg/yr for
along the eastern coast provinces in streams and rivers the first time. Subsequent annual production more than
that are connected to the sea. As a medium‐sized crab doubled to reach 522 893 kg in 2003, and to 905 741 kg in
(50–80 mm carapace width as adults), the Chinese mit 2015. Since there are about 140 000 megalopae/kg, this
ten crab has traditionally been regarded as a culinary latest figure amounts to > 1.2 × 1011 megalopae–an astro
delicacy in China. However, during the 1960s and 1970s, nomical number.
the E. sinensis fisheries collapsed due to overfishing and
habitat destruction. This stimulated increased research Despite grow‐out of the Chinese mitten aquaculture
efforts to develop aquaculture of this species in the 1970s occurring all over China, the hatcheries are mainly
and 1980s, with particular emphasis on hatchery tech located in the Yangtze River Delta in southern China,
niques. Successful mass production of crab ‘seed’ in where the majority of megalopae are produced and
hatcheries was reported in both natural and artificial
seawater in the 1980s. ‘Seed’ of Chinese mitten crab are
800
Production (Thousand t) 600
400
200
0 1995 2000 2005 2010 2015
1990
Figure 23.3 Adult male of the Chinese mitten crab, Eriocheir Figure 23.4 Annual aquaculture production of the Chinese mitten
sinensis, showing its ‘mittens’. Source: Reproduced with permission crab, Eriocheir sinensis, in China from 1990s to 2015. Data from FAO
from John Lucas. 2015. Source: Reproduced with permission from John Lucas.
transported to other parts of the country for grow‐out. Freshwater Decapod Crustaceans 531
For example, of 905 741 kg megalopae produced in 2015,
829 047 kg was produced in Jiangsu province located in 23.3.3.1 Hatchery
the Yangtze River Delta. Outside the Yangtze River Delta, Obtaining high quality broodstock crabs is the first step
the most important region for hatchery production of to successful hatchery operation. Ideally, female brood
Chinese mitten crab is along the Liao River in northern stock crabs should be between 125–150 g and males
China, producing 67 500 kg in 2015 (China Fisheries should be larger than 150 g. Only healthy active crabs
Statistical Yearbook 2016). with intact appendages are selected and crabs collected
from lakes and streams are generally preferred to those
23.3.2 Biology from pond cultures. Broodstock nutrition is crucial dur
ing the ovarian maturation period in late September to
The Chinese mitten crab inhabits fresh water streams mid‐November. The diets commonly used to feed brood
and lakes, favouring habitats with clean water and lush stock include fresh natural food, such as trash fish,
aquatic plants. They are omnivorous and nocturnal. Chaeturichthys stigmatia; the razor clam, Sinonovacula
Their diet includes aquatic plants and insects, small mol constricta; and sandworm, Nereis japonicus. Specifically,
luscs, fish, shrimps, and earth worms. Aquatic plants formulated diets supplemented with essential fatty
often make up the bulk of their gut contents, probably acids have also been developed for female broodstock
due to their ready availability. The crab has broad (Wu et al., 2007; 2009).
temperature tolerance and can survive between 1 °C and
35 °C; however, in winter when temperature drops below Following conditioning, male and female broodstock
5 °C, the crabs often hide in holes and feeding ceases. crabs are put together with a female: male sex ratio of
The Chinese mitten crab can tolerate long periods of 2–2.5:1, and brackish water is introduced to initiate
starvation and can survive without feeding for more than mating. The optimal salinity and temperature range for
one month. inducing copulation is 14–20 ‰ and 8–12 °C, respectively.
Hard sandy or muddy substrate is provided to facilitate
The Chinese mitten crab is catadromous; they spend the attachment of newly extruded eggs to the female
most of their life in freshwater but must migrate to the abdomen. Soon after brackish water is introduced, the
sea to breed. In the wild, the sexually mature crabs begin crabs will pair, and mating and spawning ensue. Egg‐
migrating downstream in late autumn and females attain carrying crabs may be found the day after mating and,
ovarian maturity in tidal estuaries. After mating and after a week, 70–80% of females carry eggs. Most females
spawning, the extruded eggs are attached to the female’s spawn within two weeks of mating. Such a spawning
pleopods. Females may continue seaward, overwintering induction process helps generate synchronised spawning
in deeper waters but returning to shallow water in the and enables hatcheries to arrange the most suitable time
spring for the hatching of their eggs. for rearing larvae. The fecundity of Chinese mitten crabs
is relatively high, with females of 100–200 g producing
Larval development of the crab occurs in brackish 200 000–900 000 eggs.
water. The newly‐hatched larvae are the planktonic first
instar zoea (Zoea I). They go through five zoeal instars After spawning, female crabs carry their eggs on their
(Zoea I to Zoea V) before metamorphosis into the mega pleopods beneath their abdomen while the embryos
lopa stage, which is crab‐like, but swims with its abdomi develop. This takes 2–4 months depending on water
nal appendages. This life cycle is similar to that of the temperature that can be manipulated in the hatchery to
portunid marine crab, Scylla serrata (Figure 6.6). either speed up or slow down embryonic development.
Megalopae migrate with tides upstream and metamor
phose to become the first stage juvenile crabs, which Three major larval culture techniques, i.e., indoor
become benthic. The juvenile crabs continue migrating intensive and outdoor semi‐intensive or extensive, have
inland into various freshwater systems where they will been developed for the Chinese mitten crab:
grow until they reach sexual maturation with a terminal
moult. The crabs undergo 15 moults over a period of 23.3.3.2 Indoor Intensive Larval Culture
about two years to reach the terminal moult, which indi Indoor intensive larval culture is mainly carried out in
cates sexual maturity and maximum size. indoor concrete ponds or tanks with temperature con
trol. A typical pond size is about 5 × 5 × 2 m, and tem
23.3.3 Culture Methods perature is normally controlled at 18 °C for Zoea I but
increased by 1 °C as larvae moult to each next zoeal
The production cycle for E. sinensis normally takes two instar. It is therefore about 24 °C by the time larvae moult
years and involves three distinct culture phases: to megalopae. Microalgae, live prey such as rotifers,
hatchery, nursery and final grow‐out. Artemia nauplii, and copepods (harvested from the
wild), as well as frozen rotifers and egg yolk, are com
monly used to feed the larvae. The initial stocking den
sity is typically 200 000–500 000 larvae/m3, and megalopa
532 Aquaculture concentrations of 200–400 thousand cells/mL), larvae
can moult to Zoea II in about 5 days without additional
production is usually 150–500 g/m3, or 20 000–70 000 feeding. If microalgae are not growing well, Zoea I and II
megalopae/m3. Survival is generally 10%–15%. larvae may be given supplementary feeds, such as soy
bean milk and dry powder of Spirulina. From Zoea III
There is usually limited water exchange during larval onward, larvae are fed mainly live Artemia nauplii, as
development from Zoea I– Zoea III; however, a higher well as frozen adult Artemia and copepods harvested
percentage of water is exchanged after larvae reach Zoea from the wild (section 9.6). The yield of megalopae is
III and, as larvae reach megalopa stage, water is usually 15–30 g/m3 for semi‐intensive systems.
exchanged twice daily. Antibiotics, such as tetramycin or
tetracycline, are often used. The optimal salinity range The ponds for extensive larval culture are often rectan
for larval rearing is 20–25‰, although megalopae can be gular and usually built in high intertidal zones. As such,
reared in salinities between 10–30‰. Both natural salt a 1.5 m deep channel (loop channel) is dug around the
water or specially formulated artificial seawater can be perimeter of each extensive pond, which buffers the
used. The latter is mainly for the inland areas and incurs pond water from abrupt temperature fluctuations asso
higher costs; therefore, it is less commonly used. To ciated with tides, since fluctuations in temperature may
acclimatise megalopae to freshwater, salinity reduction lead to mass larval mortality. Twenty to 50 days prior to
typically begins 3 days after the majority of larvae have stocking with larvae, ponds are disinfected by applying
become megalopae and salinity is reduced to < 5‰ by 1500 –2000 kg of lime (CaO)/ha or 750–1000 kg bleach
the time megalopae are 6–7 days old. The whole larval ing powder (Cl > 30%)/ha. The ponds are then filled with
culture cycle, including the time for megalopa acclimati 40–50 cm of filtered seawater about 7 days prior to
sation, is 22–24 days. Megalopae of 6 to 7 days old, stocking larvae and may be fertilised to stimulate algal
weighing ca. 140 000 megalopae/kg, may be sold to farm growth. Normally little water exchange is carried out
ers for nursery culture in freshwater. during larval culture. Initial stocking density is generally
less than 10 000 larvae/m3. Live rotifers, Brachionus sp.,
23.3.3.3 Outdoor Larval Culture are the main feed for all larval instars except Zoea I (not
Outdoor larval culture is mainly carried out in earthen fed). Zoea II and III larvae are fed about 35–40 kg of
ponds without temperature control. The earthen ponds rotifers (wet weight)/ha/day to maintain a density of
are normally built near estuarine areas, ideally with 2000–3000 rotifers/L. Rotifer feeding increases to
smooth hard clay bottoms, and capable of taking in both 70–80 kg/ha/day and 120–130 kg/ha/day at Zoea IV and
saline water (20–25‰) and freshwater. This outdoor lar V, respectively. At later larval instars, especially for Zoea
val culture technique has set a new hatchery trend in V and megalopae, rotifers may be supplemented with
China in recent years and become very popular because frozen copepods or Artemia. The rotifers used to feed
it requires fewer facilities (e.g., buildings, heating and the larvae are often reared in earthen ponds next to the
aeration systems). It is also substantially cheaper to setup larval culture ponds, with a 1:1 ratio of pond areas.
and run, and is easier for farmers to operate. In addition, Additional rotifers can also be purchased from farmers
antibiotics are not used in such systems and the quality who specialise in producing rotifers in earth ponds to
of megalopae produced is believed to be generally more supply the mitten crab hatcheries. The rearing of rotifers
robust. They are therefore favoured by the crab farmers. is largely based on fermented organic fertiliser and in a
This method has recently become the dominant hatch period of 20–35 days, 900–1 000 kg can be produced per
ery production method, producing the majority of mega hectare. The yield of megalopa is low and variable from
lopae for farming in China. extensive larval culture, ranging from 1–7.5 g/m3.
The outdoor larval culture technique can be further The major features of different larval culture methods
divided into two types: semi‐intensive and extensive. for the Chinese mitten crab are summarised in Table 23.2.
The former generally uses small ponds of 400–700 m2
equipped with aeration, while the latter is conducted in 23.3.3.4 Nursery
bigger ponds of 1–1.5 ha without aeration. Production The hatchery‐produced megalopae sold to nursery farms
of megalopae per unit volume of water is higher for the are normally transported in wooden boxes. The wooden
former, but the costs are also higher (Table 23.2). boxes are about 60 × 46 × 10 cm in size with an opening
Outdoor larval culture takes place mainly during mid‐ on each side to allow air exchange. The bottoms and the
to late‐spring when water temperature ranges between sides of the boxes are lined with mesh net to prevent
10–23 °C. escape. Prior to transport, the boxes are soaked in water
for 12 hr and a layer of clean aquatic plants or wet towel
For semi‐intensive larval culture, the typical ponds are is laid to provide moisture and avoid accumulation of
either square or round, with ca. 1.5 m water depth. Initial megalopae in one area. Each box can be loaded with
stocking density is 20 000–30 000 newly‐hatched zoeae/
m3. If the ponds are well fertilised with a good microal
gae bloom (often Isochrysis sp. and Platymonas sp. at
Freshwater Decapod Crustaceans 533
Table 23.2 Main features of three different larval culture techniques for the Chinese mitten crab, Eriocheir sinensis, in China.
Outdoor culture
Culture methods Indoor intensive Outdoor semi‐intensive Outdoor extensive
Culture ponds Concrete ponds or tanks Earthen ponds Earthen ponds
Pond areas (m2) 12–30 400–700 10 000–15 000
Stocking density 200 000–500 000 20 000–30 000 ≤10 000
(ind./m3 of newly‐
hatched Zoea‐1) Algae, egg yolk. Artemia Algae, soybean milk, Live rotifers (the main diet) and
Diets of Zoea 1– 5 larvae nauplii, rotifers and copepods Artemia nauplii algae
Artemia nauplii, frozen adult Artemia nauplii frozen adult Live rotifers (the main diet), frozen
Diets of Zoea 5 and Artemia, and copepod Artemia and copepods adult Artemia, and copepods
megalopae Yes No No
Antibiotic used? Only for Zoea 1– 2 Yes Sometimes
Probiotic use? 150–500 15–30 1–7.5
Megalopae yield (g/m3) 10–15 5–10 2–4
Survival to megalopae (%) 600–1200 500–1000 300–500
Cost for producing 1 kg of
megalopae Variable good good
(in Chinese Yuan)* 22–24 28–30 28–30
Megalopa quality
Duration of larval culture 18–24 10–23 10–23
(days) (controlled) (not controlled) (not controlled)
Temperature (°C)
* Yuan is approximately 0.15 USD.
Source: Reproduced with permission from Chaoshu Zeng.
about 0.5 kg of megalopae and 5–10 boxes can be stacked The majority of coin‐size crabs are 7th–8th juvenile
together. If conditions permit, the temperature during stage crabs.
the transportation should ideally be controlled between
14–18 °C. Using this method, megalopae survival can be The nursery ponds are generally rectangular and
near 100% if the transportation time is less than 12 hr or from a few hundred square metres to 0.25 ha in area. If
about 90% if it is about 24 hr. the first and second stages of nursery culture are in sep
arate ponds, the ponds for the first stage nursery are
The nursery phase of Chinese mitten crab culture smaller. The second stage nursery can also be con
takes 5–8 months and can be divided into two stages. ducted in rice fields with appropriate modifications
The first stage lasts about 20–30 days, during which (Figure 23.5). Firstly, structures to prevent escape and
hatchery produced megalopae are cultured in earthen access by predators (e.g., frogs and toads) must be built.
ponds to reach the 2nd–5th crab stages with a weight This is normally done by setting up a mesh fence of
between 0.1–0.2 g. The size of such juvenile crabs is simi about 1 m high on the edges of either ponds or rice
lar to that of soybeans; therefore, they are named bean‐ fields (Figure 23.5). Secondly, an encircling channel
size crabs. The second stage nursery is to grow bean‐size needs to be dug around the perimeter inside the fence.
crabs to bigger 3–10 g juveniles that are ready for stock The channel is typically 1 m wide and 60–90 cm deep.
ing into grow‐out ponds or enclosures. The second nurs This deeper channel serves as a r efuge for the crabs on
ery stage takes several months and can either use the hot days. For both the first and second stage nursery,
same ponds that were used for the first nursery stage or aquatic macrophytes, such as Vallisneria spiralis,
the bean‐size crabs may be stocked to other ponds or Hydrilla verticillata and Elodea sp., are usually planted
rice fields, which is more common. The sizes of juvenile prior to stocking, and serve as both food and shelters
crabs produced at the end of the second nursery stage for the crabs.
are similar to that of coins or buttons, therefore, they
are known as coin‐size crabs or button‐sized crabs. The initial stock density for the first nursery stage is
about 100 megalopae/m2 or 7.5 kg/ha. When megalopae
534 Aquaculture
Figure 23.5 Nursery culture ponds for Chinese mitten crabs. Source: Reproduced with permission from John Lucas.
are first stocked, the water depth is normally maintained grow‐out of Chinese mitten crabs occurs mainly in three
at 20–30 cm, but this is gradually increased by 10, 15 forms, i.e., pond, net enclosure, and rice field culture.
and 20–25 cm when crabs moult to the 1st, 2nd, and 3rd
crab stage, respectively. The maximum water level is Pond grow‐out uses earthen ponds and the size of the
70–80 cm. ponds is generally between 0.6–2 ha with a water depth
of 1.5–1.8 m. Fences similar to those of nursery ponds
During the nursery phase, crabs feed on natural diets, (Figure 23.5) are erected to prevent escape and access by
including plankton, aquatic plants and small benthic ani predators. Prior to crab stocking, the ponds are normally
mals that grow naturally in the ponds or rice fields. disinfected with lime (2000–3000 kg/ha) and 10 days
Supplementary feeds, such as corn, wheat, pumpkin, and after the disinfection, aquatic plants, such as Vallisneria
minced trash fish, as well as formulated feeds are also spiralis, Hydrilla verticillata, Ceratophyllum demersum,
provided to enhance their growth. Potamogeton maackianus, and Myriophyllum spicatum,
may be introduced to the ponds to grow. Meanwhile, one
A major problem during the nursery culture of Chinese month or so prior to crab stocking, live mud snails,
mitten crabs is the precocious puberty of some juvenile Bellamya purificata, a favourite food for mitten crabs,
crabs. It is common that 15–30% of crabs harvested may be stocked at the rate of 3500–4500 kg/ha and left to
from nursery ponds show precocious development. reproduce in the ponds. Finally, fertilisation using fer
Such crabs, weighing only 15–35 g, have reached their mented organic fertilisers is often applied 10–20 days
terminal moult (i.e., maximum size) and will not grow before crab stocking to increase the natural biomass
any further. Therefore, they have very low or no market inside the ponds.
value. Research has shown that such a phenomenon is
linked to genetics, culture environment (e.g., high water The stocking density of coin‐size crabs for pond cul
temperature) and nutrition (Wu et al., 2010); however, ture is normally about 7500 crabs/ha and they are often
techniques are yet to be developed to effectively control polycultured with various freshwater fish and shrimp,
its occurrence. which may be stocked at different times. The important
consideration for fish species selection for polyculture is
23.3.3.5 Grow‐out that their feeding habits should complement rather than
Depending on the farm and location, either later in the compete with Chinese mitten crabs. Over the culture
year before winter sets in or early in the following year, period, water quality needs to be closely monitored,
the coin‐size crabs harvested from nurseries are stocked DO should be about 5 mg/L, pH 7–8.5 and Secchi disc
for grow‐out to market size of between 80–200 g. The reading 50–80 cm. The yields per hectare per year are
Freshwater Decapod Crustaceans 535
Figure 23.6 Rice (paddy) field culture of Chinese mitten crabs in northern China, showing rice field newly stocked with coin‐sized crabs.
Source: Reproduced with permission from John Lucas.
variable, depending on intensity of polyculture, but they market size crabs, although higher yields of close to
are usually close to 1000 kg of market‐sized crabs, 1000 kg/ha have been reported.
together with twice that weight of various freshwater
fish and shrimp. The paddy‐field culture systems integrating rice pro
duction and Chinese mitten crab grow‐out are more
Net enclosures (hapas) have been used for grow‐out in commonly practiced in northern China (Figures 23.6
many inland lakes in China. Polythene with mesh sizes of and 23.7). Rice fields need modifications for such
1–2 cm is a common net material. The nets are fixed in purposes, which include setting up fences, digging
place with bamboo stakes. The net walls are folded perimeter channels and planting aquatic plants, simi
inwards and held on to the bottom with heavy rocks, lar to those for nursery culture described above. One
causing them to sink into the mud. The upper edge of of the main d ifferences between the two is that the
the net is typically 50–60 cm above the water level. channel needs to be deeper than for nursery culture, at
Site selection is important for net enclosure culture and about 1.5 m. In addition, a small pond (100–200 m2
suitable sites must have good water quality, slow water with 1.5 m depth) is often dug for acclimatisation and
flow, stable water level as well as suitable depth (1–2 m); temporary culture of coin‐size crabs. It can also be
and, most importantly, abundant submerged aquatic used for temporary storage of market‐sized crab dur
plants and high benthos biomass. ing harvesting.
Stocking density for net enclosures range from Stocking density ranges from 1–1.5 coin‐size crabs/m2
1500–9000 crabs/ha. For some enclosures, crabs can for the paddy‐field culture. As the paddy‐fields grow rice
totally rely on the natural food. For others with lower simultaneously, the water depth is normally kept low at
natural biomass, the mud snail, Brachmia purificata, 5–10 cm. Water needs to be exchanged more regularly
may be stocked at 6000–7500 kg/ha prior to crab stock due to low levels and extra care needs to be taken to
ing and sometimes again after stocking. Other supple avoid large fluctuations in water temperature. As the
mentary diets including chopped trash fishes, and natural benthic biomass in the rice fields is relatively low,
cooked corn and wheat may also be provided at a food the crabs need regular feeding with supplementary feeds,
ration of 7–8% crab biomass/day. Survival is normally such as corn, wheat, trash fish, trash shrimp or mud
about 40–50% for net enclosure grow‐out. The method snails, once or twice daily. These feeds are normally
normally yields higher profitability because water quality cooked to avoid fouling water in the shallow system.
is better, the crab can utilise abundant natural foods and, With proper management, rice field culture can often
due to lower stocking density, crabs can grow to larger achieve yields of 300–450 kg/ha, and up to 750 kg/ha.
sizes with substantial high market values. Generally, the Although crabs will feed on rice plants, they also feed on
yield from net enclosure culture is about l50–450 kg/ha nuisance insects and weeds, and may even improve rice
536 Aquaculture
Figure 23.7 Rice (paddy) field culture of Chinese mitten crabs in northern China, showing rice plants are ready for harvesting. Source:
Reproduced with permission from John Lucas.
production. As such, the integrated culture system pro that are commercially important (Holdich, 2002). Among
duces rice that is largely ‘organic’ with higher market farmed species:
value; hence the economic benefits are substantial. ●● Astacus astacus is mainly farmed in Europe.
23.3.4 Market and Marketing ●● Pacifastacus leniusculus is farmed in Northern
The Chinese mitten crab is largely consumed domesti
cally in China (Figure 23.8) although it is also exported to America and Europe.
countries or cities that have large ethnic Chinese popula ●● Cherax destructor, C. albidus, C. quadracarinatus and
tions, such as Singapore. Female crabs with well‐
developed ovaries and large crabs normally fetch C. tenuimanus are mainly farmed in Australia.
substantially higher prices. ●● Procambarus clarkii, the red swamp crawfish2, is by far
23.4 Freshwater Crayfish the most important species. While the native distribu
tion of P. clarkii is north‐eastern Mexico and south‐
23.4.1 Farmed Species central USA, particularly in Louisiana, the species has
Freshwater crayfish have been an item of human food been introduced widely to other parts of the USA and
for thousands of years. However, of more than 500 rec many countries worldwide. As a result, this species is
ognised species, there is only a small number of species now the most widely distributed freshwater crayfish in
from the genera Astacus, Procambarus and Cherax the world and has become an important freshwater spe
cies for both fisheries and aquaculture (Huner, 2002).
2 ‘Crawfish’ is used for this species, but it is a freshwater crayfish like
the other species treated here, and will tend to be identified as a
freshwater crayfish in this text.
Freshwater Decapod Crustaceans 537
Figure 23.8 Chinese mitten crabs, Eriocheir sinensis, for sale individually and in gift boxes. Source: Reproduced with permission from
Chaoshu Zeng.
Figure 23.9 Female red swamp crawfish,
Procambarus clarkii, with newly
independent juveniles that have detached
from her abdominal appendages
(pleopods). Source: Reproduced with
permission from Chaoshu Zeng.
23.4.2 Production Status dramatically reduced due to the outbreaks of crayfish
The noble crayfish A. astacus is a species widely distrib plague (section 10.5.2.2) in the past century.
uted in Europe and it has been an object of trade and
commerce in the continent for more than 2 000 years. The red swamp crawfish, P. clarkii (Figure 23.9) has
It is recognised as a delicacy and widely used in been commercially farmed in its native USA since 1950s
French cuisine. However, its abundance in Europe has and is now farmed in most states in the southern USA.
By 1986, the area of farming had reached 50 000 ha with
538 Aquaculture largest quantity. It was estimated that prior to 1990 the
annual fisheries harvest was only a few thousand tonnes,
average annual harvests of 30 000 t or more in most years. but by 1995 it had increased dramatically to 65 500 t/yr
However, in the 1990s production declined to < 8000 t, and by 1999, almost 100 000 t/yr. The substantial increase
largely due to two major factors: in P. clarkii fisheries production was largely driven by the
1) Large volumes of peeled crayfish meat imported from establishment and rapid growth of the processing indus
try, which produced peeled crayfish meat (tail meat) for
China were sold for prices below USA production export to the USA and Europe, during the early 1990s.
costs. For example, during the 3 years from 1992–1995, the
2) Dry weather patterns led to a major reduction in both crayfish tail meat exported to the USA increased by 8
wild and farmed crayfish production in Louisianan times; and in 1999 out of the ca. 100 000 t/yr production,
(Huner, 2002). at least 70 000 t was channelled into export. The large
More recently, production in the USA increased again volumes of cheap tail meat imported to USA from China
as imports from China declined and it was > 60 000 t seriously impacted the P. clarkii farming industry in the
in 2014. USA (above). Meanwhile, over‐exploitation of P. clarkii
Beyond the USA, P. clarkii has been farmed on a lim in China led to a sharp decrease in the wild stocks. The
ited basis in Spain, France, Italy, and Zambia; however, decrease in wild crayfish stocks and capture harvests
an explosive growth in aquaculture production of the generated much interest in aquaculture of the species
species in mainland China in the past decade has dwarfed with massive growth in aquaculture production after
the production from these countries (Figure 23.10). As a 2000 (Figure 23.10): aquaculture production of P. clarkii
consequence, the following sections will mostly describe in 2003 was 44 000 t; it increased to 364 000 in 2008 and
its production in China. reached 723 207 t in 2015.
P. clarkii was introduced to mainland China from
Japan in 1929. Established local populations were first While prior to 2000, P. clarkii production in China
confirmed in Jiangsu and Anhui provinces in southern was mainly for export, since the turn of the century
China. Harvested wild P. clarkii began to appear in there is a new phase that is driven by a dramatic increase
domestic markets in the 1950s and by the 1960s and in domestic market demand. This is largely attributed to
1970s it had become commonly known in the market. the creation of several very popular brand‐named
Meanwhile, wild populations of P. clarkii had become culinary delicacies for P. clarkii, such as ‘spicy small
widespread along the middle and lower reach of the lobster’, ‘aromatic small lobster’ and ‘savory whole small
Yangtze River, and it became a dominant species in lobster’. There was also a very successful marketing
w etlands of the region. Harvests of wild P. clarkii also strategy of renaming the crayfish as ‘small lobster’ and it
grew to become one of the most important freshwater is now consumed in small to large restaurants all over
fisheries in China with Jiangsu province producing the the country. The sharp increase in domestic market
demand has seen the price of P. clarkii increases dra
800 matically and even the processing industry for export
has diminished as it is now more profitable to sell the
600 China whole, live crayfish to domestic restaurants than to
Production (Thousand t/yr) export their meat.
400
Several native species belonging to the genus Cherax,
200 redclaw (C. quadracarinatus), marron (C. tenuimanus)
and yabbies (C. destructor and C. albidus), are farmed
USA commercially in Australia. They have also been intro
duced overseas for farming, where they have become
0 1995 2000 2005 2010 feral in some countries. Marron and yabbies originate in
1990 south‐western and south‐eastern Australia, respectively,
and are adaptive to cooler climates compared with the
Figure 23.10 Annual aquaculture production of the red swamp redclaw crayfish which is a tropical species native to
crawfish, Procambarus clarkii, in China from 1990s to 2015. Data from northern Australia. Although the number of aquaculture
FAO 2015. Source: Reproduced with permission from John Lucas. farms for these species increased rapidly during the
1980s and 1990s, and production peaked at 423 t in 2001,
prediction that the industry would further expand and
produce thousands of tonnes in following decades failed
to materialise. The number of farms and production
declined in recent years to only 131 t in 2014. Major
Freshwater Decapod Crustaceans 539
problems include the generally small‐scale of farms, so
that best practice technologies are not widely adopted,
and the total production volume is too small. Local
m arkets appear to be satiated while the low volume of
production has severely hampered the potential for
exploiting lucrative overseas markets.
23.4.3 Biology Figure 23.11 A female Alleghany crayfish, Orconectes
obscurus,with large eggs attached to the appendages (pleopods)
Freshwater crayfish occur in a wide range of habitats, of the animal’s abdomen. Source: J. Montemarano 2008.
including lakes, rivers, swamps, cave pools, temporary Reproduced under the terms of the Creative Commons
ponds, and estuaries. There are potentially few freshwa Attribution license, CC BY 3.0.
ter habitats that crayfish could not invade. Some species,
such as P. clarkii and the yabby, C. destructor, are well movement of her pleopods. When the young hatch, they
adapted for borrowing. cling to the female’s pleopods and undergo moults dur
ing which they do not feed but rely on their yolk reserves
Freshwater crayfish are opportunistic omnivorous, to survive. They are unable to survive away from the
feeding on a wide range of food items, including micro female until they have completed their second moult and
bially‐enriched plant detritus, benthic and planktonic then they assume an adult‐like appearance and begin to
invertebrates, plant seeds and succulent green plant live independently (Figure 23.9) (Huner, 2002).
material where available (Huner, 2002). The dietary
preferences may change at different life stages of the Compared to other commercially important decapod
crayfish as animal food occurs more frequently in guts crustaceans, the simple life cycle of freshwater crayfish is
of young crayfish and appears to be more crucial for advantageous for aquaculture. The absence of planktonic
new hatchlings (Huner, 2002). Under farm condition, free‐living larval stages makes freshwater crayfish rela
crayfish readily consume a variety of formulated feeds, tively easy to cultivate as populations in culture ponds
including grain‐based, low protein livestock feeds, high can be self‐sustaining, and mature crayfish can be simply
protein fish and crustacean feeds, and raw seeds or by‐ stocked into the ponds to start a population.
products of those seeds, such as corn, rice and soybeans
(Huner, 2002). Like other crustaceans, growth of crayfish is achieved
via periodic moulting (section 6.4.2). One interesting
Unlike the mitten crab and freshwater prawns, crayfish feature of freshwater crayfish in relation to moulting is
show relatively minor sexual dimorphism in their gen their ability to reuse calcium from the old exoskeleton.
eral anatomy (except redclaw whose mature males show When the moult approaches in freshwater crayfish, the
distinguished red patches on their chelae), although old exoskeleton demineralises. Calcium is withdrawn
males typically reach a larger size under farm conditions. and stored in paired hemispherical stones, known as gas
Freshwater crayfish have enlarged chelae as their first troliths, which are located adjacent to the stomach.
legs, but these are similar in size and differ little Following moulting, the gastroliths dissolve, and calcium
between the sexes (except in redclaw). Nevertheless, is absorbed into the circulatory system to be redeposited
males and females can be distinguished by the difference into the new exoskeleton. This mechanism conserves
in gonopore location, i.e., the gonopores of males calcium in freshwater environments where it is at rela
are located on the bases of the 4th walking legs while tively low levels.
these are on the bases of 2nd walking legs in females.
Females do not need to moult in order to mate. During As for other crustaceans, freshwater crayfish suffer
mating, the male deposits the sperm mass on the ventral from a range of diseases caused by various pathogens,
surface of the female between her walking legs. As eggs parasites, and commensals. Among them, the most dev
are extruded through the gonopores on the bases of the astating of all is the crayfish plague caused by the fungus,
walking legs during oviposition, they are fertilised by the Aphanomyces astaci. Crayfish plague is a fatal disease
sperm mass. During oviposition, the female releases a that can lead to rapid mortality of the infected crayfish
mucus‐like substance called glair from glair glands to
attach the fertilised eggs to her pleopods (broad abdomi
nal appendages) for brooding (Figure 23.11). The incu
bation period largely depends on temperature and
species: for P. clarkii, it takes 18–22 days at 22–24 °C, but
more than 4 months when temperature is lower than
10 °C. The female gently agitates the eggs by systematic
540 Aquaculture per animal (Romano and Zeng, 2017), and may produce
crayfish of inferior condition to those grown under
and often the loss of whole populations (Evans and field conditions.
Edgerton, 2002). The crayfish plague outbreaks were
responsible for elimination of native crayfish popula There are generally two situations where intensive
tions in many European waters during the past century. culture is used:
However, to date it has not been reported as a major
problem in North America, China or Australia (Evans 1) Like the soft‐shell crab industry, freshwater crayfish
and Edgerton, 2002). The susceptibility of different cray are captured in the field and placed individually into
fish species to the disease appears to vary, for example, tanks, where they are kept until moulting. The newly‐
the North American species, including the red swamp moulted crayfish are chilled before re‐calcification of
crawfish P. clarkii, are more resistant to the disease the shell, and the soft‐shelled crayfish are sold to
(Evans and Edgerton, 2002). gourmet food markets.
23.4.4 Aquaculture Attributes 2) When the juvenile crayfish emerge from the protec
Freshwater crayfish possess some important attributes tion of the female in a pond, they are very vulnerable
that make them good candidates for aquaculture. These to predation, either from larger individuals of their
include: own species and other predatory fauna. Higher rates
●● a simple life cycle without planktonic larval stages that of survival may be obtained through these early
stages by having ovigerous (egg‐bearing) females in
require special live prey and larval culture facilities; separate hatchery tanks and removing the female or
●● feeding on inexpensive, low protein, and grain‐based the eggs before she has a chance to eat the detached
juveniles. The juveniles are then reared in intensive
diets, as well as natural organic matter in their conditions. This technique may be used in large‐scale
environment; hatcheries for stocking ponds and restocking wild
●● physically and physiologically robust with broad envi populations.
ronmental tolerance;
●● fast growth to market size with appropriate feeding; 23.4.5.2 Semi‐Intensive Culture
●● some species, such as redclaw, are not very aggressive Pond Culture
or cannibalistic; Ponds for culturing redclaw crayfish, C. quadracarinatus,
●● the desirable lobster‐shape helps marketing; are generally about 0.1–0.25 ha in size with a depth of
●● texture and flavour are comparable to marine crusta between 1.3–1.8 m in farms located in tropical Australia.
ceans; and The ponds are generally elongated for more efficient
●● there are often good markets for their products. food distribution and V‐shaped in the bottom to allow
easy drainage. Perimeter fencing is installed around the
23.4.5 Culture Methods pond site to exclude predators. Complete netting enclo
23.4.5.1 Intensive Culture sure (top and sides) of the culture ponds is also essential
The attributes of freshwater crayfish outlined above are where bird predation is prevalent. Various hides, such as
very favourable for pond culture, where they may gain a used car tyres, bundles of synthetic mesh, PVC pipes and
substantial component or all their nutrition from the crates, are placed on the bottom of the pond to increase
organic matter present in the environment. Even the water column utilisation and provide refuge for the red
feeds that are given to promote growth are inexpensive; claw (Figure 23.12). Depending on the farm, feeding may
hence crayfish are relatively inexpensive to produce in be conducted with commercial grain‐based pellets and
pond culture. there may be mechanical aeration (Figure 3.13).
However, some crayfish species are not well suited to In the case of P. clarkii, there are substantially very
high density intensive culture because of their aggression large numbers of farms spread over a vast geographic
and cannibalism. For example, the marron, C. destructor, range in China, so the techniques used for pond culture
is particularly cannibalistic, and the yabby, C. tenuimanus, vary considerably. The following describes some of the
shows a high degree of aggression. Cannibalism of more popular methods.
newly‐moulted soft‐shelled animals is especially
common during early juvenile stages (Romano and The most commonly used ponds for culturing
Zeng, 2017). As a result, intensive crayfish culture may P. clarkii in China are rectangular earthen ponds of
include retention of individual crayfish in individual between 0.4–1.0 ha. Various structures, such as plastic
compartments within a culture system. However, this sheets or aluminium plates of about 0.5 m high, are
requires relatively high capital and management inputs erected around the pond to prevent escape. The length
to width ratio of culture ponds is generally about 2:1,
with pond banks having a slope of at least 1 in 3.
Freshwater Decapod Crustaceans 541
Figure 23.12 Artificial substrates used to provide hides for pond cultured freshwater crayfish. These are being used for the redclaw
crayfish, Cherax quadracarinatus, in north Queensland, Australia. The netting stretched above the ponds is a barrier to water birds that
prey on the crayfish. Source: Reproduced with permission from Chaoshu Zeng.
Water depth is generally between 1.0–1.5 m and the sub diversified food sources for the crayfish. Overall, the area
strate is no more than 10 cm deep in mud. A channel of for planting aquatic plants is about 30–60% of the total
about 2 m in width and 0.3 m in depth is dug along the pond area. Additionally, the Chinese mystery snails,
length of the pond and is used to temporarily hold Bellamya chinensis, may also be stocked into crayfish
crayfish during harvesting when the pond is drained. ponds in spring. They may be stocked at a rate of
300–450 kg/ha and left to reproduce inside the ponds.
Prior to stocking crayfish, ponds are drained and disin The early juveniles of the snail have a fragile shell that can
fected with lime (750–1500 kg/ha), which is followed by easily be crushed by crayfish, thereby providing crucial
fertilisation with organic fertiliser (2250–4500 kg/ha). animal protein. The filter feeding of the snails also helps
Several days later, water is introduced through a long sieve maintain good water quality in the culture ponds.
bag with a mesh size of ca. 60 µm to prevent introducing
predators or their eggs. The pond is then first filled to The crayfish seed used for pond culture are mainly
about 50 cm deep and various aquatic plants are planted from two sources:
both in the pond and along the banks. These include 1) Juveniles of 2–3 cm long (5 g on average) are pur
Elodea nuttallii, Hydrilla verticillate, Alternanthera
philoxeroides, Pistia stratiotes, Ceratophyllum demersam, chased from a hatchery for stocking the ponds. This is
Eichhornia crassipes, Zizania caduciflora, Vallisneria normally carried out in spring and stocking density is
s piralis, Lemna paucicostata, Myriophyllum spicatum, about 20–30 crayfish/m2. With 3 months of culture in
Potamogeton crispus, and Potamogeton sp. A combination summer, some crayfish can reach market size and
of rooted aquatic plants in shallow water with floating can be harvested. The remaining crayfish are farmed
plants in deeper water can provide more abundant and further and harvested intermittently.
542 Aquaculture As with pond culture, paddy‐fields are stocked with
either adult or juvenile crayfish:
2) Sexually mature crayfish of ca. 30 g are stocked in 1) Adult crayfish are stocked into paddy‐fields during
ponds in late summer at about 20 000 individuals/ha
with a female: male ratio of 1.5–2:1. The crayfish are later summer/autumn to produce juveniles for cul
well fed to prepare for overwintering. By spring of ture during the following year. Rice is planted the fol
next year, the early juveniles produced by breeding lowing year without tilling.
adults stocked the year before are living indepen 2) Paddy‐fields are stocked with juvenile crayfish in
dently and the adult crayfish can be harvested. As spring after rice has been planted. The water level in
soon as crayfish juveniles are independent of females, the paddy‐field must be managed: when juvenile cray
they are fed with soy milk, minced trash fish, pig’s fish are first stocked it must be kept low, but with the
blood, and soy cakes. These diets have a higher com growth of crayfish and rice, the water depth is gradu
ponent of animal protein than those used for adults. ally increased to 12–15 cm.
With increasing growth of the juveniles, the feeding Water quality needs to be monitored and fresh water
rate is reduced from initially 20% of biomass to about introduced regularly. The use of insecticides for rice is
10% and the plant content of the diet can be increased avoided whenever possible. If they have to be applied,
to become the major component. only low toxicity and low residue types can be used since
crayfish are also arthropods.
During grow‐out, crayfish may be fed a variety of Crayfish are more commonly harvested before the rice
inexpensive diets such as wheat, corn, peanut cake, is harvested; however, some farmers harvest rice first,
wheat bran, trash fish and formulated feed (crude pro and then refill the paddy‐fields to continue crayfish cul
tein content: 25–28%). Crayfish may be fed twice a day ture for a further 1–2 months to produce larger crayfish.
in summer but only once every two weeks in winter. With proper management, the crayfish yields of paddy‐
Feeding is adjusted according to water temperature; field culture can reach 3000 kg/ha together with rice pro
water quality and observation of the amount being duction of around 6000 kg/ha.
consumed. Just before harvest, however, animal diets
may be fed at an increased ratio to enhance growth Polyculture
and the quality of meat. Pond culture of crayfish P. clarkii in China sometime also
involves stocking with one or more other aquaculture
The yields of pond culture vary according to the level species for polyculture. For example, the silver carp,
of husbandry but are often 3000–6000 kg/ha, i.e., Hypophthalmichthys molitrix, is often stocked with
e quivalent to some shrimp farm yields. P. clarkii in pond culture. The stocking rate for silver
carp normally ranges from 700–1100 fish/ha. The silver
Paddy‐field Culture carp is chosen for polyculture because it filters feeds on
Paddy‐field culture, which integrates rice production zooplankton and is not a threat to small and newly‐
and crayfish farming, has gained popularity in China moulted crayfish.
over recent years. With vast rice fields available in China
suitable for such farming it has huge potential for further 23.4.5.3 Extensive Culture
expansion. While there is a clear demarcation between intensive and
semi‐extensive culture of freshwater crayfish, there is
Paddy‐fields of 0.7–1.7 ha are generally considered to often no clear demarcation between semi‐intensive and
be most suitable for crayfish culture and daily manage extensive culture.
ment, but they need to be modified for crayfish culture.
Major modifications include a channel dug around the Extensive culture of P. clarkii in China is often carried
perimeter of the paddy‐field about 0.5–1.0 m inside the out in fields used for lotus, Nelumbo nucifera, farming.
levee. This channel is typically 3–5 m wide and 0.8– Such systems are generally more extensively managed
1.0 m deep. For large paddy‐fields, cross channels or than paddy‐field culture systems for P. clarkii and,
double cross channels are also dug. Channels may make as such, the crayfish are normally stocked at lower
up 20–25% of the paddy‐field surface area. Inside the densities. There is also extensive culture of P. clarkii in
channels, aquatic macrophytes are planted prior to large natural water bodies, such as shallow and vegetated
stocking. The channels may also be treated with organic rivers, lakes and marshes, and other types of wetlands.
and inorganic fertilisers to encourage the growth of Some of this involves stock enhancement or ranching
freshwater rotifers, Daphnia, and aquatic insects, which with the release of juvenile crayfish to supplement wild
are important foods for early juveniles. populations.
There must also be structures to prevent crayfish from
escaping, and these are commonly mesh fences around
the perimeter of rice‐fields (cf. Figure 23.6).
23.4.6 Markets and Marketing Freshwater Decapod Crustaceans 543
Freshwater crayfish are sold whole, live or frozen (cooked
or uncooked), and as fresh or frozen tail meat (abdomi Macrobrachium rosenbergii (Figure 23.14) is indige
nal muscle) in the USA and European markets. Whole nous to south and southeastern Asia, northern Oceania,
soft‐shelled crayfish are also produced and sold in the and the islands of the western Pacific. It is a traditional
USA, and these fetch a substantially higher price. food source throughout this range (Figure 23.15).
However, in mainland China domestic demand for the M. rosenbergii can grow rapidly to a large size (up to
red swamp crayfish targets mainly live and hard‐shelled 200 mm) under culture conditions, and based on this
products, and consumption is often in restaurants. Due favourable trait it now supports significant aquaculture
to its popularity, market demand for crayfish is expected efforts. The potential of M. rosenbergii for aquaculture
to continue rising in China. This is likely to drive further has resulted in its translocation to regions outside its
expansion of the P. clarkii aquaculture industry that natural range, including Hawaii, South America, and the
may also include other crayfish species, such as redclaw, Caribbean, as well as China, where it supports success
C. quadricarinatus. Redclaw was recently introduced to ful aquaculture industries. The oriental river prawn,
mainland China from Taiwan and farming of this species
is expanding rapidly.
23.5 Freshwater Prawns Figure 23.14 Lateral carapace of a male Macrobrachium
rosenbergii. Source: J. Tuszyński 2009. Reproduced under the terms
The commercial freshwater prawns are species of the of the Creative Commons Attribution Share Alike License
genus Macrobrachium, family Palaemonidae and within CC‐BY‐SA‐3.0 (http://creativecommons.org/licenses/by‐sa/3.0).
the Infraorder Caridea. They are characterised by their
very long and slender second pair of legs (Figure 23.13).
There are more than 150 Macrobrachium species which
can be found in inland freshwater bodies and estuaries
throughout the world. From an aquaculture perspective,
the giant river prawn or Malaysian prawn, Macrobrachium
rosenbergii, and the oriental river prawn, M. nipponense,
are the two main species farmed.
Figure 23.13 A male giant river prawn, Macrobrachium species, Figure 23.15 Giant river prawns, Macrobrachium rosenbergii, in ice
produced by a Bangledeshi aquaculture farm. Source: Reji Jacob on sale in a supermarket, Udonthani, Thailand. Source: Wolf‐Dieter
2008. Reproduced under the terms of the Creative Commons 2008. Reproduced under the terms of the Creative Commons
Attribution Share Alike License CC‐BY‐SA‐3.0. Attribution Share Alike License CC-BY-SA-3.0.
544 Aquaculture M. amazonicum (in Brazil), M. vollenhovenii (in Ghana),
M. lamarrei and M. idella (in India) (New, 2005), and
M. nipponense, is smaller than M. rosenbergii with a M. spinipes (in Australia).
maximum length of about 100 mm. It inhabits fresh and
brackish waters throughout much of eastern Asia, but is 23.5.2 Biology
of particular commercial importance in China. M. nip- There is variability between species of Macrobrachium
ponense shows relatively broader tolerance of variations in some aspects of their biology relevant to aquaculture.
in temperature and salinity, and its high survival in colder This is particularly true regarding the influence of
climates has facilitated its development as an important salinity during reproduction, which reflects their origi
aquaculture species, especially in China (New, 2005). nal marine origin and the varying degrees of adaption to
freshwater between species. The following account of
23.5.1 Production Status the biology and farming of freshwater prawns will focus
Aquaculture production of M. rosenbergii almost specifically on M. rosenbergii, which is the most widely
d oubled between 2000 and 2014, while aquaculture pro farmed species of freshwater prawn.
duction of M. nipponense increased by almost three
times over the same period. Production of M. nipponense 23.5.2.1 External Anatomy
now exceeds that of M. rosenbergii (Table 23.3) and this The rostrum of Macrobrachium species is a relatively
production is exclusively from China. Furthermore, long, toothed, and laterally flattened extension of the
China contributes about 60% of the global production carapace (Figures 23.13 and 23.14). The first and second
of M. rosenbergii (Table 23.4). Other species of pair of legs in Macrobrachium are chelate (Figure 23.13).
Macrobrachium which have shown aquaculture poten The first pair is used for picking small epiphytic food
tial or are being investigated for this potential, include organisms from solid substrates while the second pair is
M. malcolmsonii (in India and China) (Table 23.3), very long and slender, and much larger in males than in
females. The reproductive openings of males and females
Table 23.3 World aquaculture production of the giant river are located at the bases of the fifth and third pair of
prawn, Macrobrachium rosenbergii, the oriental river prawn, thoracic legs, respectively. Backward escape movements
M. nipponense, and the monsoon river prawn, M. malcolmsonii, result from rapid contraction of the abdomen and tail
in 2000 and 2014.* while large pleopods or swimmerets allow effective
swimming.
2000 production (t) 2014 production (t)
23.5.2.2 Life Cycle
M. rosenbergii 130 689 216 538 M. rosenbergii grows to maturity in freshwater. The
M. nipponense 87 139 257 841 courtship display of males includes waving antennae and
M. malcolmsonii _ 142 head bobbing. Then copulation between a mature male
Total 217 828 474 321 and a recently‐moulted, soft‐shelled female results in
deposition of a sticky sperm bundle (spermatophore) on
* http://www.fao.org/fishery/statistics/global‐aquaculture‐production/ the ventral thoracic region of the female. Eggs are
query/en extruded through the genital pores 6–20 hr after mating
and are fertilised as they pass across the spermatophore
Table 23.4 Aquaculture production (t) of the giant river prawn, into the brood chamber, formed by the downward elon
Macrobrachium rosenbergii, and the Oriental river prawn, gation of the lateral regions of the abdominal exoskele
M. nipponens, in 2014 from the major producing countries.* ton. During egg laying the female bends the tail forward
to the thoracic region to assist this process. Oviposition
M. rosenbergii M. nipponense of a complete batch of eggs usually take about 20 min.
The eggs are held in bundles by an elastic membrane
China 127 204 257 841 secreted by the setae to which they are attached. Newly
Bangladesh 45 187 – extruded eggs are slightly elliptical, about 0.6 mm long
Thailand ca. 18 000 – and bright orange in colour. A large female may produce
India 8680 – up to 100 000 eggs and they can spawn 3–4 times per
Taiwan 8557 – year under natural conditions. Incubation takes about
Indonesia 1809 – 19 days at 26–28 °C and throughout this period, pleo
pods beat back and forth intermittently to provide water
* http://www.fao.org/fishery/statistics/global‐aquaculture‐ movement. Egg‐bearing females move downstream into
production/query/en
saline regions of estuaries and the orange colour of Freshwater Decapod Crustaceans 545
the eggs gradually changes to dark slate grey after
16–17 days when the larvae inside the eggs are fully to ensure that water quality is at its highest at night when
developed. Hatching of the planktonic larvae and their the larvae moult.
dispersal is assisted by vibrations of the pleopods.
Recirculation hatchery systems enable larvae to be cul
From hatching to metamorphosis, the actively swim tured at higher densities than in flow‐through systems.
ming larvae undergo 11 moults (11 larval stages are rec Such systems generally utilise continuous circulation
ognised) to metamorphose into postlarvae, which take of larval culture water and must incorporate a range of
3–7 weeks depending on temperature, water quality, and technologies such as particle filtration, biofiltration
food supply. Larvae feed on zooplankton. Postlarvae and UV irradiation, to maintain adequate water quality
become benthic and migrate upstream from saline con (section 3.5.1). Recirculation hatchery systems conserve
ditions to complete their life cycle in freshwater. water and reduce demand for seawater or brine.
The hatchery may be established inland, near grow‐out
23.5.3 Culture Methods facilities, using seawater/brine transported to the site or
Farming techniques for M. rosenbergii are summarised artificial seawater.
in the following. For a more comprehensive review of
methodology, please refer to New (2002). Newly‐hatched Artemia nauplii (Figure 9.7) are the
major live feed used for Macrobrachium larval culture.
23.5.3.1 Hatchery Freshly hatched brine shrimp (Artemia) nauplii are
Because M. rosenbergii completes its larval life in brack added to larval culture systems after day 2 and feeding
ish water, while postlarvae and adults live in freshwater, rate is increased as larvae grow. For example, early‐stage
hatcheries are usually located near sources of both fresh M. rosenbergii larvae may be fed at a rate of 5–6 nauplii/
water and seawater (although artificial seawater can be larva (0.15 nauplii/mL), whereas older larvae may receive
used). Ovigerous females may be obtained from the wild 60 nauplii/larva (1.8 nauplii/mL) (Roustaian et al., 2001).
or from farmed prawns and should be held at salinity ca. Larval cultures are ideally fed up to 5 or 6 times a day.
5‰ until the eggs hatch. Larvae can be siphoned from Feeds other than Artemia are also used extensively in
hatching tanks, counted and placed into separate larval larval culture of Macrobrachium to reduce the cost.
rearing tanks or the hatching tanks may become the lar These include fish roe, ‘egg custard’ and formulated diets
val rearing tanks once the females are removed. In some (New, 2002).
hatcheries, the females are kept in the larval rearing
tanks in cages, which facilitates easy removal of the The first appearance of postlarvae occurs in culture
females by taking out the cages once hatching has tanks at 16–20 days old and their presence is indicated
occurred. The salinity for larval culture is 9–19 ‰ but is by a change in behaviour from free swimming larvae to
optimal at about 12‰ for all larval stages, while the opti postlarvae that crawl on or cling to the tank surfaces.
mal water temperature is 28–31 °C. M. rosenbergii larvae Newly metamorphosed postlarvae are 7–8 mm long and
can be cultured in either flow‐through or recirculating they are generally acclimated to freshwater before being
hatchery systems. harvested and transferred to nurseries (New, 2002).
Survival to the postlarvae stage during hatchery culture
In flow‐through hatchery systems, larval culture tanks is generally about 40–60%.
are stocked at relatively low densities (30–50 larvae/L).
Water is exchanged on a regular basis at a rate of about 23.5.3.2 Nursery
50 % per day. The new water is either filtered ‘clear water’ The nursery phase is concerned with culturing postlar
or ‘green water’ which is enriched with batch cultured vae to subsequent juvenile stages before stocking into
microalgae (e.g., Chlorella, Nannochloropsis, Isochrysis grow‐out ponds. Indoor nurseries can utilise a range of
and Tetraselmis species) or algae bloomed in outdoor tank types with a surface area of 10–50 m2 and a water
tanks. The microalgae improve water quality by remov depth of about 1 m. Tanks can be stocked at densities in
ing nitrogenous wastes excreted by the prawn larvae. It is the range of 1000–2000 postlarvae/m2. Artificial sub
believed that the larvae do not get much direct nutri strates such as nylon screens or netting are often added
tional benefit by ingesting the microalgae although it to provide shelter and increase surface area to support
may be eaten by zooplankton, which in turn are con greater survival. Water is aerated and can be supplied
sumed by the prawn larvae: thus indirectly providing from a flow‐through or recirculating system and may be
nutritional benefits to the larvae. The benefit of green heated. Postlarvae are fed at a rate of about 10–20% of
water culture is that it may increase production by their total weight per day and feeds commonly include
10–20% compared to clear water culture. It is important crumble diets as well as fresh foods such as beef liver, egg
custard or minced fish (New, 2002). Up to 90% survival
can be achieved by 20 days and high survival can be
maintained if density is reduced as the postlarvae grow.
Postlarvae can be harvested using 3 mm dip nets.
546 Aquaculture Figure 23.16 Harvesting batch cultured Macrobrachium
rosenbergii. Although not yet large prawns, some males are
Outdoor nursery facilities utilise earthen ponds showing an early stage of enlarged arms. Source: Reproduced with
stocked with 70–800 postlarvae/m2. Higher stocking permission from Chaoshu Zeng.
densities are supported by providing additional sub
strates, supplementary aeration and protection from Grow‐out ponds for M. rosenbergii may also be man
predators. Postlarvae and early juveniles are generally aged using a continuous culture system where there is
fed with formulated feeds at a similar rate to those in regular harvesting of market–sized prawns and restocking
indoor nursery systems. Survival to 0.8–2.0 g, at which of postlarvae. This system is widely employed in the trop
juveniles can be harvested using a 5–6 mm seine net, in ics where prawn growth is continuous, and ponds may be
outdoor nursery ponds is about 75%. emptied only after several years. Selective h arvesting usu
ally begins after 4–9 months to remove market‐sized
23.5.3.3 Grow‐out prawns. This procedure may be repeated monthly and
Grow‐out culture of M. rosenbergii may be extensive, could yield about 2000–4000 kg/ha/yr. Harvesting costs
semi‐intensive, or intensive. are increased in such systems compared to batch culture,
and predators and competitors may become established in
Extensive Culture ponds over longer culture periods. Continuous harvest
This is generally conducted in earthen ponds or and the regular removal of larger prawns support greater
impoundments, such as reservoirs, irrigation ponds and productivity by reducing intraspecific aggression and
channels, and rice fields. Postlarvae or juveniles are allowing more energy to be channeled for growth.
stocked at a low density (1–4 individuals/m2) and there is However, some large dominant prawns may evade capture
little (if any) intervention relating to water quality, stock and influence the growth of underlings.
management, and there is no supplementary feeding.
This system is most widely used in Asia and productivity Freshwater prawns are omnivorous and their nutri
is generally less than 500 kg/ha/yr. tional requirements are not particularly demanding.
Successful semi‐intensive pond culture of M. rosenbergii
Semi‐Intensive Culture relies on provision of supplemental feeds. These are
This is the widely practiced culture system for commonly farm‐made feeds formulated from locally
M. rosenbergii and the most common in tropical areas.
Semi‐intensive culture is usually conducted in purpose‐
built ponds and involves management interventions
relating to water quality maintenance, stocking, feeding,
pond fertilisation and predator control. Ponds are u sually
stocked with hatchery raised postlarvae or juveniles at a
density of 4–20 individuals/m2.
In batch culture grow‐out systems, the whole pond is
harvested by draining after 6– 9 months when prawns
have reached marketable size of 20–60 g (Figure 23.16).
Production ranges from 1000 kg/ha/yr to 3000 kg/ha/yr,
depending on the culture period and initial stocking
density. However, M. rosenbergii show a phenomenon
called heterogeneous individual growth (HIG) where
some individuals grow at a much faster rate than oth
ers, become dominant, and stunt the growth of others.
Batch culture, as a consequence of this, yields a crop of
non‐uniform sized prawns. Modified batch culture
systems have been developed where larger prawns
are removed from the culture or prawns are split into
different ponds to reduce densities to allow smaller ani
mals to grow to market size (New, 2002). In the former
case, ponds are still stocked only once but selective har
vesting begins when the first batch of prawns reach
market size. Smaller prawns are then able to grow, and
this process supports several harvests. The 9–12 month
production cycle is terminated with a final harvest and
draining of the pond.
available animal or vegetable matter such as rice, vegeta Freshwater Decapod Crustaceans 547
ble waste, and trash fish. A protein content of about
30–35% is considered optimal. Commercially made pel crayfish, dominated by the red swamp crawfish,
leted feeds are also used and some are specifically formu Procambarus clarkii; and freshwater prawns, domi
lated for M. rosenbergii, but they are relatively expensive. nated by Macrobrachium rosenbergii and M. nippon-
Feeding rate is usually reduced from about 10–20% of ense. The mitten crab, crayfish and freshwater prawns
body weight for juveniles to about 2% of body weight are ranked 2nd, 3rd and 4th in global crustacean aqua
near harvest (New, 2002). However, rations are adjusted culture production, respectively, after shrimp.
in response to observations of feeding activity, particu ●● The mitten crab Eriocheir sinensis is only farmed in
larly in ponds where there is regular harvesting of larger China and consumed by ethnic Chinese. Despite being
individuals. a freshwater crab, copulation is induced by brackish
water and larval culture requires salinity of 20–25‰.
Grow‐out of M. rosenbergii is generally with males and Megalopae are the hatchery end‐product and unique
females together. However, culture of monosex popula outdoor larval culture techniques are becoming popu
tions (normally all male) of M. rosenbergii offers poten lar due to their low costs. There is a long nursery phase
tial higher benefits to farmers. Because males grow to a (5–8 months) with 2 phases that produce the bean‐
larger size than females, they produce a greater biomass sized and then coin‐sized juveniles. Grow‐out occurs
over a given culture period. This increased production is in ponds, enclosures, and rice fields with polyculture
also because energy that would be partitioned into commonly practiced.
reproduction in mixed sex cultures can be utilised for ●● Freshwater crayfish farming is largely based on the red
growth. Growth trials have shown that all‐male cultures swamp crawfish, Procambarus clarkii, with very lim
produced larger prawns, greater biomass, and estimated ited production from a few other species. Again, China
revenue increases of 23.5% and 85.7% compared to is the dominant producer (>90%). Freshwater crayfish
mixed populations and all‐female populations, respec have a simple life cycle with hatchlings clinging to the
tively. Although monosex populations can be obtained female’s pleopods and relying on yolk to survive until
by hand‐sexing, this is time‐consuming, labour‐intensive, becoming independent juveniles. This suppression of
and can be inaccurate. All‐male offspring can be larval stages is advantageous for aquaculture, as larval
p roduced by mating normal males to ‘neo‐females’ pro rearing is often the most technically demanding phase.
duced by surgical removal of the androgenic glands from Semi‐intensive pond culture is the most common
juvenile males or by more recently developed techniques grow‐out method, although polyculture in rice fields,
using RNA interference. as well as extensive culture in natural water bodies are
also becoming popular.
Intensive Culture ●● Freshwater prawn aquaculture is based on
This is generally undertaken in small earthen or con Macrobrachium rosenbergii and M. nipponense, the
crete ponds up to about 0.2 ha in size. Stocking density former occurring in many countries while the latter, a
is high (>20/m2) and systems require continuous aera smaller species, only in China. Similar to the mitten
tion, high water exchange, strict control of water quality, crab, their larval culture requires brackish water and
precise mangement of nutrition and food input and postlarvae are produced in hatcheries. Nursery culture
elimination of predators and competitors. Establishment may be indoors in the hatchery or outdoors in ponds.
and maintenance costs for intensive systems are high Semi‐intensive and extensive cultures are the most
and considerable technical input is required for success. common ways for grow‐out. Some males of M. rosen-
However, production levels of between 5000 and bergii grow at a much faster rate, become dominant,
10 000 kg/ha/yr are achieveable. Intensive culture may and stunt the growth of others. Furthermore, females
become more popular for M. rosenbergii as the technol are smaller than males. Various stocking/culture tech
ogy required by such systems improves and further niques (e.g., all‐male culture) and harvesting strategies
developments are made with aspects of the husbandry have been developed to mitigate this problem and
of this species (e.g., reliable production of monosex improve productivity.
populations). ●● Despite differences in their biology and culture
requirements, the main farmed freshwater decapods
23.6 Summary share some important features: there are relatively
well‐established farming techniques for them; diverse
●● Farmed freshwater decapod crustaceans are diverse culture systems may be used, including farming in rice
but all have high market values. They include the fields; they can effectively utilise natural organisms
Chinese mitten crab, Eriocheir sinensis; freshwater and plant proteins, hence reducing feed costs; they are
suitable for polyculture with diverse species. These
features are highly favourable for aquaculture.
548 Aquaculture a review on its prevalence, influencing factors, and
mitigating methods. Reviews in Fisheries Science &
References Aquaculture, 25, 42–69.
Roustaian, P., Kamarudin, M. S., Omar, H. B. et al. (2001)
Cheng, Y., Wu, X., Yang, X. et al. (2008) Current trends in Biochemical changes in freshwater prawn
hatchery techniques and stock enhancement for Chinese Macrobrachium rosenbergii during larval
mitten crab, Eriocheir sinensis. Review in Fisheries development. Journal of the World Aquaculture Society,
Science, 16, 377–384. 32, 53–59.
Wu, X., Cheng, Y., Sui, L. et al. (2007) Effect of dietary
Evans, L. H. and Edgerton, B.F. (2002) Chapter 10: Pathogens, supplementation of phospholipids and highly
parasites and commensals. In: Holdich, D. M. (Ed.). unsaturated fatty acids on reproductive performance
Biology of Freshwater Crayfish. Pp. 541–584. and offspring quality of female Chinese mitten crabs,
Blackwell Science, Oxford. Eriocheir sinensis (H. Milne‐Edwards). Aquaculture,
273, 602–613.
Holdich, D. M. (2002) Chapter 18: Conclusion. Wu, X., Cheng, Y., Zeng, C.et al. (2009) Reproductive
In: Holdich, D. M. (Ed.) Biology of Freshwater Crayfish. performance and offspring quality of Chinese mitten crab,
Pp. 673–681, Blackwell Science, Oxford. Eriocheir sinensis (H. Milne‐Edwards), broodstock fed
an optimised formulated diet and the razor clam,
Huner, J. V. (2002) Chapter 16: Crayfish of commercial Sinonovacula constricta. Aquaculture Research, 40,
importance: Procambarus. In: Holdich, D. M. (Ed.). 1335–1349.
Biology of Freshwater Crayfish. Pp. 541–584. Wu, X., Chang, G., Cheng, Y.et al. (2010) Effects of dietary
Blackwell Science, Oxford. phospholipid and highly unsaturated fatty acid on
gonadal development, tissue proximate composition,
New, M.B. (2002) Farming freshwater prawns. A manual lipid class and fatty acid composition of precocious
for the culture of the giant river prawn Chinese mitten crab, Eriocheir sinensis. Aquaculture
(Macrobrachium rosenbergii). FAO Fisheries Technical Nutrition, 16, 25–36.
Paper. No. 428. FAO, Rome. 212 pp. [http://www.fao.org/
docrep/005/y4100e/y4100e00.htm] (accessed
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recent research and a glance at the future. Aquaculture
Research, 36, 210–230.
Romano, N. and Zeng, C. (2017) Cannibalism in decapod
crustaceans and implications to their aquaculture:
549
24
Bivalve Molluscs
John S. Lucas
CHAPTER MENU 24.6 Introductions and Other Environmental Issues, 564
24.1 Introduction, 549 24.7 Industry Reviews, 565
24.2 Aspects of Biology, 550 24.8 The Future of Bivalve Aquaculture, 570
24.3 Farmed Bivalves, 552 24.9 Summary, 570
24.4 Phases of Bivalve Aquaculture, 555 References, 571
24.5 Farming Problems, 560
24.1 Introduction farming methods. The techniques for individually
h andling pearl oysters, a high‐value species, are totally
Oyster farming has a history going back to Roman times inappropriate for lower value species which must typi-
and mussel farming began in Europe more than 700 years cally be farmed in large numbers for an economically
ago. They probably began before this in Eastern Asia. It viable operation.
was relatively easy to farm shore‐inhabiting species such
as cupped oysters (not flat oysters1 or pearl oysters) and Aquaculture production of molluscs was 15.5 million
mussels, and to make the transition from harvesting wild t in 2013; valued at USD17.8 billion. This ranks them
stocks to farming them. Substrates, such as rocks and third in both quantity and value of global aquaculture
stakes, were added to promote recruitment in areas of production (Figure 1.2). There has been a steady growth
natural settlement. Then, where someone or some group in aquaculture production of molluscs in recent decades,
had rights to harvest these stocks at consumable size, this i.e., there was mean growth in global mollusc production
constituted a simple form of aquaculture. by weight of 5.2 % / yr from 1993 to 2013. This was
less than the 7.1% / yr increase in global aquaculture
Bivalves are excellent aquaculture material because, (Table 1.1).
after their larval stages, they can be reared using r elatively
simple technology and they don’t have to be fed. Bivalves By far the greatest source of mollusc production is
obtain their food by filter feeding particulate organic bivalves. There is some aquaculture of gastropods, most
matter (POM), including phytoplankton, from the prominently abalone (Chapter 25). There are low‐
water around them. There are no costs for feeds in the technology aquaculture industries in China for a
grow‐out phase of farming: a very important advantage. p lethora of marine gastropod species which are listed in
The different modes of life and range of commercial FAO statistics as ‘seashells’ and which amounted to
values of various bivalves, however, require different 902 thousand t in 2013. Farming the Chinese mystery
snail, Cipangopaludina chinensis, in freshwater yielded
1 ‘Oysters’ is used for edible oysters. There are two major groups of >100 000 t in that year.
edible oysters: ‘cupped’oysters, which live with one valve fused to the
substrate, and ‘flat’ oysters, which are free‐living with similar valves. Global capture fisheries for molluscs produced
There is another bivalve group known as oysters: the pearl oysters. 6.9 million t in 2013, i.e., less than half the amount
They will always be identified as ‘pearl oysters’. from aquaculture. Global capture varied between 6.3
and 7.6 million t/yr over the two decades 1993–2013,
reflecting the variability intrinsic to fisheries.
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.
550 Aquaculture Figure 24.2 The two valves of a black‐lip pearl oyster, Pinctada
margaritifera, showing the inner nacreous layer and the rough
24.2 Aspects of Biology outer periostracum. The pearl may be added for effect or it may be
a ‘blister’, i.e., where the nacreous layer has covered an object on
24.2.1 Morphology the inner surface of the shell. Source: Reproduced with permission
The following is a brief generalised description of bivalve from John Lucas.
morphology. Gosling (2003) provides a more compre-
hensive description for representative species. freshwater mussels, cockles and clams. (By the way,
freshwater and marine mussels are totally unrelated.)
The name bivalve arises from these animals’ most Associated with the foot there may be a gland that
prominent and dominant feature: a shell consisting of secretes threads, byssal threads, by which the bivalve
two valves that are joined along a hinge and enclose the lives attached to its substrate.
body. Each valve usually has a prominence near the
hinge, the umbo, which is the oldest part of the valve. Extending across between the valves are one or two
There are often concentric lines on the shell reflecting large muscles, anterior and posterior adductor muscles,
previous valve sizes (Figure 24.1). Each valve consists which close the valves. Lining the valves and enclosing
of three layers, the outer periostracum, the medial the visceral mass are two thin lobes, the mantle lobes.
prismatic layer and the inner nacreous layer. They are These reach to the edges of the valves and secrete the
made up of calcareous and proteinaceous material. material for shell growth and thickening. The cavity or
The most important layer for aquaculture is the inner chamber enclosed by the mantle lobes is called the
nacreous layer, which is often lustrous and very hard: m antle cavity and it contains the gills on each side of
the ’pearly’ layer of pearl oysters and pearl mussels the body. The gills consist of fused parallel filaments.
(Figure 24.2).
Bivalves have no identifiable head. The body is laterally
compressed within the valves and mainly consists of a
soft visceral mass: gut, kidney, gonads, blood vessels, etc.
There is a ventral foot, which may be insignificant in
sedentary species such as marine mussels and oysters
or very well developed in burrowing species such as
Figure 24.1 The shell of a giant clam (Tridacna gigas) showing 24.2.2 Filter Feeding
numerous growth lines over its 25+ years of growth. The growing Bivalves obtain their nutrition by filtering fine particu-
shell edge is uppermost. Source: Reproduced with permission late organic matter (POM), including phytoplankton,
from John Lucas. bacteria and organic detritus, from suspension in the
water column around them. They may also obtain some
nutrition by direct uptake of dissolved organic matter
(DOM) from seawater across the large permeable sur-
faces of their gills and mantle chamber. A water current
is created through the mantle cavity by cilia on the gills.
The gills’ fine structure is basket‐like and particles are
trapped by cilia lining the microscopic surfaces. These
particles are bound in mucus and directed anteriorly to
the mouth in food channels. Palps at the mouth sort the
particles, rejecting large particles, inorganic particles
and excessive numbers of particles as mucus‐bound
‘pseudofaeces’. Ingested food particles are digested
Bivalve Molluscs 551
600 (L∞) to which bivalves grow. Low POM levels result in
sub‐optimal food intake, slow growth, stunted size and
reduced reproductive output.
Energy uptake (J/hr) 400 24.2.4 Anaerobic Metabolism
Anaerobic metabolism is a particular aspect of bivalve
200 physiology. Bivalve morphology gives a level of protec-
tion against many adverse conditions: the valves may be
0 held tightly closed for long periods as protection against
0 2 4 6 8 10 adverse conditions such as desiccation, salinity varia-
Concentation of unicellular agae (mg/L) tions, pollution, and predators seeking entry into the
mantle cavity. This behaviour, however, limits oxygen
Figure 24.3 Rate of energy obtained by a bivalve from filter availability and periods of prolonged valve closure are
feeding versus concentration of suspended microalgae. As the accompanied by anoxic conditions within the mantle
concentration of microalgae increases the pearl oyster obtains cavity, reduced metabolic rate and anaerobic metabo-
more food, then beyond the optimum concentration the food lism, which are well tolerated. It is best developed in
intake and digestion rate progressively decline as the feeding intertidal and bottom‐inhabiting species, such as
mechanism is choked. The pearl oyster, Pinctada maxima, is oysters, mussels, clams and cockles. A practical conse-
feeding on the microalga Isochrysis species. Source: Reproduced quence of this behaviour and biochemistry for aquacul-
with permission from John Lucas. ture is that it is better to hold most bivalves in
non‐desiccating conditions out of water during trans-
within the gut and undigested material compacted into portation and marketing than to keep them crowded
faeces and expelled. The volume of water ’pumped’ together in polluted conditions in water.
through the gills per unit time may be impressive. Pearl
oysters are among the highest with values for large 24.2.5 Reproduction
individuals being >1000 L/day (Yukihira et al., 1999). Sexuality is not strongly fixed in some bivalves and
individuals may change sex during a breeding season or
There is often an optimum range of particle concentra- between seasons depending on prevailing conditions or
tions that maximises food intake while minimising food in response to nutritional status or as an age‐related
wastage. When feeding bivalves with unicellular algae phenomenon. Cupped oysters, pearl oysters, marine
cultures, e.g., in conditioning bivalve broodstock or rear- and freshwater mussels, and clams usually have sepa-
ing larvae and juveniles, it is not sufficient to load the rate sexes (dioecious), and often have similar propor-
water with as high a density of algae as possible to max- tions of each sex in populations. However, some oysters
imise food intake and growth. This is wasteful and may and clams change sex according to the patterns
be detrimental to growth due to clogging of the feeding described above. Most scallops are simultaneous her-
processes (Figure 24.3). Optimum cell concentration maphrodites, with separate male and female sections to
varies with algal species. This relates to the size, other the gonad, and a few species are protandrous sequential
physical characteristics and acceptability. The optimum hermaphrodites, being males when young then switch-
cell concentration usually increases through the life cycle ing to female. Giant clams are an example of pro-
in bivalves. It may range from ca. 10 000 cells/mL for tandrous hermaphroditism, where the gonad initially
early larval stages, to ca. 50 000 cells/mL for late larval matures as a testis and then later oogenic tissue devel-
stages, to ca. 100 000 cells/mL for juveniles and >100 000 ops in close proximity with the spermatogenic tissue in
cells/mL for adults. the gonad.
24.2.3 Growth
Growth in bivalves is such that the size/age relationship Most temperate and higher‐latitude bivalve species,
follows the pattern described in section 6.4.1. POM and many tropical species have a distinct breeding sea-
levels strongly influence growth rates and the final size son that is primarily related to water temperature.
Typically, gametogenesis occurs during the late winter to
early summer months, with progressive accumulation of
mature gametes in the gonad. Then spawning occurs
with numerous individuals spawning synchronously
through being triggered by pheromones released with
gametes by nearby individuals (section 6.2.3).
552 Aquaculture 24.3 Farmed Bivalves
While histological studies may be used in research on There are six main groups of farmed bivalves:
bivalve reproductive seasonality, such techniques are not ●● clams and cockles;
appropriate for industry. Viewing the size and colour of ●● oysters;
the gonads through open valves to identify their degree ●● marine mussels;
of development and sex is usually enough. ●● scallops;
●● freshwater pearl mussels; and
24.2.6 Life Cycles ●● pearl oysters.
Most bivalve life cycles consist of planktonic trocho- The quantity and value of aquaculture production of
phore, veliger and pediveliger larval stages, and then these six groups is shown in Figure 24.4. The relative
metamorphosis to a juvenile, called a spat (Figure 6.3). importance of clams and cockles, which are not a major
Some variations from this pattern occur in flat oysters component of the seafood industry in many countries, is
and freshwater mussels, where the early larval stages are from China’s production of >4 million t/yr, much of it for
retained within the mantle cavity of the female and home consumption. China dominates bivalve produc-
released late in development. tion, being responsible for ca. 77% of production by
weight and ca. 64% by value.
Bivalve eggs are usually quite small, 40–100 μm diam-
eter, and very numerous. Fecundity ranges from about a Quantities and values of some bivalves that support
million eggs per spawning, e.g., flat oysters, to tens of major industries are shown in Table 24.1.
millions, e.g., cupped oysters, to hundreds of millions
per spawning in the largest giant clam (Tridacna gigas). 24.3.1 Oysters (Family Ostreidae)
There are vast numbers of bivalve sperm released at the As previously indicated there, there are two kinds of
time of egg spawning. The sperm have a small head, a commercial oysters
few μm in diameter, and a long flagellum. The sperm ●● cupped (or rock) oysters (Crassostrea and Saccostrea
swim vigorously when in good condition.
species), with the lower (left) valve cemented to a hard
The mature sperm is haploid (n) but the mature egg substrate (Figure 7.7); and
is tetraploid (4n) until a sperm penetrates its outer ●● flat oysters (Ostrea species) (Figures 24.5A, 24.5B),
membrane. The fertilised egg then undergoes two mei- which live unattached on soft substrates.
otic divisions. These are evident by the successive ejec-
tions from the egg of two small polar bodies, each 6000 Value 6000
containing discarded haploid chromosomes from a 4000 Quantity 4000
meiotic division. The resulting haploid egg nucleus is
then ready to merge with the sperm nucleus to form a Quantity (103 t) 2000 2000 Value (Million USD)
diploid embryo.
00
The embryo commences mitotic division involving
the whole cytoplasm and passing through 2, 4, 8, etc., Oysters
cell stages. It develops into a ciliated trochophore larva, Clams
usually within 24 hr at normal temperatures for the Mussels
species. The trochophore rapidly develops into a MOuysstseeSlrcppalleeoaarrllpsss
bivalved veliger, which is also known as a D‐stage
because of its shape (Figure 6.3). The veliger swims and Figure 24.4 Annual production of the six major groups of bivalves
feeds on POM with a ciliated lobe, the velum. Towards in 2013.2 Source: Reproduced with permission from John Lucas.
the end of its planktonic life, which typically lasts 2–4
weeks, the veliger develops a prominent foot to become 2 The values for pearls are very approximate.
a pediveliger (see Figure 26.13). The pediveliger settles
on a substrate that it selects and then it metamorphoses
into a spat. Metamorphosis involves absorption of the
velum, development of gills and a gill‐based feeding
mechanism, and attachment to the substrate with byssal
threads or other means.
There follows a period of growth without abrupt
changes in morphology (Figure 6.3). Sexual maturity is
typically reached in about two years. Many bivalves are
quite long‐lived: age can be measured from annual
growth lines in cross‐sections through a valve, like
growth rings in a tree stump.
Bivalve Molluscs 553
Table 24.1 Global aquaculture production of some major bivalve
molluscs in 2014.*
Species Quantity Value
thousand t Million USD
Pacific oyster† 4775 3796 Figure 24.5b Flat oysters, Ostrea edulis from Logonna‐Daoulas,
(Crassostrea gigas) 3896 3642 France Source: Gilbert le Moigne. Reproduced under the terms of
Japanese carpet shell 1851 3268 the Creative Commons Attribution Share Alike License CC-BY-SA-3.0.
(Ruditapes philippinarum) 1756 3323
Yesso scallop‡ 720 649 from a range of families are included in this assemblage.
(Patinopecten yessoensis) 449 564 Their common features are that most are free‐living and
Marine mussels (Mytilidae) burrow in particulate substrates.
Constricted tagelus or razor clam
(Sinonovacula constricta) They include:
Blood cockle (Anadara granosa) ●● the blood cockles (Anadara species);
●● the Japanese carpet shell or Manila clam (Ruditapes
* Data from http://www.fao.org/fishery/statistics/global‐aquaculture‐
production/query/en philippinarum); and
† The major oyster producer, China, only reports ‘cupped oysters’ in ●● the North American hard clam or quahog (Mercenaria
data reported to FAO, but its production is very largely this species.
‡ The major scallop producer, China, doesn’t distinguish scallop mercenaria) (of clam chowder fame).
species in data reported to FAO, but the scallop production is very The most important bivalve species in quantity and value
largely this species. is a small clam, the Japanese carpet shell (or Manila clam),
Ruditapes phippinarum (Figure 24.6A). It has a wide
Figure 24.5a Pacific oysters, Crassostrea gigas. These are natural distribution in the Indian and Pacific Oceans; but,
‘cultchless’ oysters that have been cultured unattached to a like the Pacific oyster, it has also been introduced to the
substrate (cultch), the usual habit of rock oysters. Source: Pacific coasts of North America and to Europe. China,
Reproduced with permission from John Lucas. however, accounts for about 97% of global production.
Here the clams are largely sold live in local markets.
As well as habitat and morphological differences, they
differ in mode of development. Cupped oysters spawn Giant clams (Tridacnidae) are an exception to the
gametes into the water column, while flat oysters brood usual ‘clams’. They are a small group of coral‐reef inhab-
embryos in their mantle cavity and then release larvae. iting species that are exceptional in size and in obtaining
The Pacific cupped oyster, Crassostrea gigas, has a nutrition by a combination of filter feeding and photo-
number of favourable features and has been introduced synthesis of symbiotic algae. Some species are farmed for
over a wide geographic range the tropical aquarium trade (section 26.5.3).
24.3.2 Clams and Cockles
The terms ‘clam’ and ‘cockle’ have no taxonomic signifi- 24.3.3 Marine Mussels (Family Mytilidae)
cance and bivalves with a variety of common names and Marine mussels are farmed for human consumption and
most commercial species are in two genera:
●● Mytilus species, which are temperate; and
●● Perna species, which are mainly tropical.
Mussels have similar valves. They live attached to a
firm substrate by strong byssal threads (Figure 24.6B).
Their foot becomes soon after settlement. They are
554 Aquaculture
Figure 24.6a Japanese carpet shells, Ruditapes phippinarum, Figure 24.6c Scallops, Pecten maximus. Source: Jeremy Keith.
Galicia, Spain. Source: Luis Miguel Bugallo Sanchez. Reproduced Reproduced under the terms of the Creative Commons
under the terms of the Creative Commons Attribution Share Alike Attribution Share Alike License CC-BY-SA-3.0.
License CC-BY-SA-3.0.
Figure 24.6b The Mediterranean mussels, Mytilus galloprovincialis. Figure 24.6d Freshwater pearl mussels, Margaritifera
Source: Chris,urs-o. Reproduced under the terms of the Creative margaritifera Source: M. Hafermann 2012. Reproduced under the
Commons Attribution Share Alike License CC-BY-SA-3.0. terms of the Creative Commons Attribution Share Alike Licence,
CC BY‐SA 3.0.
unusual in having gonad tissue in their mantles as well
as in the visceral mass. Patinopecten yessoensis, are the third most valuable
bivalve industry. This scallop is produced in large
24.3.4 Scallops (Family Pectinidae) quantities in China for international markets. Unlike
Species of Pecten, Aequipecten, Argopecten and most bivalves, scallops do not retain mantle water after
Patinopecten are among those commercially farmed. removal from the ocean. They can be held out of water
Most scallops are free‐living on the surface of soft sea- and sold whole for only a limited period and usually close
beds. They respond to disturbance with swimming to the site of production. Most scallop meat (adductor
movements caused by rapid ‘flapping’ of their valves, muscle with or without gonad attached) is removed from
expelling water jets. This is caused by vigorous contrac- the shells (shucked) and exported frozen.
tions of the single adductor muscle which is large, and
which is the seafood consumed from these bivalves. 24.3.5 Freshwater Pearl Mussels
Scallops tend to be circular in outline with a long promi- (Family Unionidae)
nent hinge, similar to pearl oysters (Figure 24.6C). These freshwater mussels burrow in particulate sub-
strates using a well‐developed foot. They inhabit clean
Scallops are not regarded as easy material for fast flowing streams and rivers (Figure 24.6D). The inner
a quaculture. However, scallops, mainly the yesso scallop,
nacreous layer of their shells is very lustrous and this is Bivalve Molluscs 555
the basis of pearl production. The life‐cycle of these
mussels involves suppressed larval development, a fea- 24.4 Phases of Bivalve Aquaculture
ture in common with some other freshwater inverte-
brates. Embryonic development occurs in eggs retained The complete process of bivalve aquaculture involves
in the gills. Subsequently a well‐developed and bivalved the series of phases outlined in Chapter 6 (Figure 6.3).
glochidium larva, which is a rather jaw‐like veliger The period for this complete process, hatchery produc-
hatches from the egg and attaches to the gills, fins or sur- tion to marketable size, is at least 18 months for most
face of fish hosts by an adhesive thread or hooks on its commercial bivalves. Much bivalve aquaculture, how-
valves. The glochidium larva feeds from the fish host as ever, does not involve this complete process: the com-
a parasite. The parasite gradually changes into a juvenile plete process is only used in culturing the higher‐value
bivalve, detaches from the host, falls to the substrate and species. For many cultured bivalves the process com-
assumes the adult burrowing habit. Rearing these mus- mences after natural spatfall, and the costly and techni-
sels through the glochidium stage without a fish host as cally demanding hatchery and nursery farming phases
source of nutrients proved to be difficult, but in vitro are by-passed.
farming methods have been developed recently.
24.4.1 Farming from Natural Spatfall
24.3.6 Pearl Oysters (Family Pteriidae) Substrates may be placed where bivalve larvae
Pearl oysters are tropical and subtropical marine species are completing development and seeking appropriate
occurring in a range of habitats from silty seabeds to substrates on which to metamorphose into spat. These
coral reefs. They have a vestigial foot and at least initially substrates are known as spat collectors or, specifically in
attach to a firm substrate with byssal threads. They are relation to oysters, as culch. They take a variety of forms
from the genera Pinctada and Pteria. As in pearl‐pro- depending on local industry practices and on the species’
ducing mussels, the inner shell layer, the nacreous layer, biology and its value (Figures 24.7 and 24.8). The amount
is very lustrous and this is the basis of pearl production of settlement is related to the density of larvae in the
(Figure 24.2). They have the typical larval development water flowing over the spat collectors. Thus, it is essen-
of marine bivalves. tial to deploy spat collectors at times and in areas where
there are high concentrations of late‐stage larvae. Spat
collectors shouldn’t be deployed too soon before the
Figure 24.7 Oyster spat collectors, Mengleuz, France. Source: J. Moorhead. Reproduced under the terms of the Creative Commons
Attribution Share Alike License CC-BY-SA-3.0.
556 Aquaculture
Figure 24.8 Wooden battens placed intertidally to collect oyster spat in Nelson Bay, New South Wales, Australia. Source: CSIRO
ScienceImage 2901Oyster Farming. Reproduced under the Creative Commons Attribution Share Alike license, CC‐BY 2.0.
anticipated time of larval settlement as the surfaces may tangled coils of fishing line are often used for scallop
become heavily bio‐fouled and discourage larvae from larvae, which seem to prefer sheltered and concealed
settling. Spat may be collected in areas of high larval substrates.
settlement and the collectors then transported to the
subsequent farming sites. 24.4.2 Farming from Hatchery Production
Bivalve hatcheries have a number of common
Different kinds of larvae chose different surfaces on components:
which to settle: ●● a source of uncontaminated seawater;
●● Oyster larvae tend to prefer a hard, rough surface that ●● treatment of the water intake, e.g., fine filtration and
is not greasy, and is clear of silt and algae. Culch used temperature control;
for them includes wooden sticks, flexible plastic strips, ●● pumps;
oyster shells, cement tiles, mangrove tree branches ●● broodstock holding and conditioning tanks;
and bamboo. ●● larval rearing tanks;
●● Fibre substrates such as frayed ropes are commonly ●● nursery rearing tanks; and
used as spat collectors for mussels, which attach to ●● a facility for mass‐culturing of microalgae (unless a
them at very high densities. The natural densities of
spat on the settlement substrates are generally too commercial diet is being used) (section 9.2).
high, jeopardising growth and survival. They are often The components and their operation are described in
stripped from the settlement substrate, tearing their detail by Sarkis (2007) in relation to the installation and
byssal thread attachments to this substrate. They are operation of a modular hatchery.
allowed to re‐attach to vertical ropes at controlled
densities for further growth. Similar spat collection 24.4.2.1 Spawning Induction
materials are used for pearl oysters (Figure 2.13). Often little more than stress is required to induce
●● Suspended coarse‐mesh bags containing filamentous spawning of ripe bivalve broodstock. The stress may be
substrates such as monofilament gill netting and
exposure to elevated water temperature for a tolerable Bivalve Molluscs 557
period or to air for several hours. Addition of some
chemicals to seawater containing the broodstock may of triploids. Triploids are largely infertile (see below), but
induce spawning, e.g., hydrogen peroxide, potassium some produce eggs and these have been used to produce
chloride and ammonium hydroxide. UV irradiation of tetraploids by blocking one of the meiotic divisions of the
the seawater, which produces free oxygen radicals, may triploid egg nucleus.
also stimulate spawning. Serotonin, a neurotransmitter
substance, injected directly into the gonad (e.g., 0.2–0.5 mL The advantages of triploidy have been particularly
of 10‐3 molar solution) is effective in inducing spawning used for the Pacific oyster. Triploids differ from diploid
in a variety of bivalves. oysters in having larger cell nuclei and cells to accom-
modate the additional set of chromosomes; but, more
When one individual sheds eggs or sperm (usually importantly, they show poor gonad development and
sperm, males tend to be more easily triggered to spawn), don’t spawn out during the summer months, as do dip-
the gametes can be spread into the vicinity of other loids. They maintain good meat condition throughout
individuals to stimulate them with the gamete the year and are available for marketing when the dip-
pheromones. loids are in poor condition post‐spawning. Furthermore,
where the market does not want ripe oysters, as in
Spawning induction may be by-passed completely North America, there is the advantage of lack of gonad
with gonad stripping. When the broodstock are known development in summer when diploid oysters are ripe.
to contain fully mature gametes, they may be sacrificed, Spawned‐out oysters generally have poor market
their gonads repeatedly lacerated with a sharp blade, acceptance. With less energy diverted to gametogene-
and the gametes washed out into a beaker. This is only sis, more energy is available for other tissue growth and
appropriate to dioecious bivalves or there would be triploids grow more rapidly than diploids, reaching
self‐fertilisation. commercial size earlier.
24.4.2.2 Fertilisation The commercial advantages of triploidy have been
Where broodstock can be sexed, the sexes are often studied in four oyster species, but so far triploidy has
placed in separate containers for spawning induction. only been adopted on a large commercial scale in Pacific
Alternatively, individuals are removed from a group as oysters (Gosling, 2003).
they commence to spawn and the kind of gametes, eggs
or sperm, is evident. The objective is to have dense 24.4.2.4 Larval Rearing
s uspensions of eggs in filtered seawater, up to one or two Modern bivalve hatcheries tend to use the following
thousand per mL, and very dense suspensions of sperm techniques:
in separate containers. The eggs may be kept in suspen-
sion with gentle aeration and their numbers estimated 1) Seawater is generally filtered down to ca. 1 μm to
from microscope counts of small subsamples in a remove silt, organic debris, zooplankters, which may
Sedgwick‐rafter counting chamber. A few mL of sperm be predators or competitors, and phytoplankton that
suspension, mixed from several males, are then added to the larvae may not be able to feed on. This requires a
the suspensions of eggs. comprehensive filtration system in the seawater
intake.
There are constraints to the amount of sperm to be
added. Too few sperm result in low levels of fertilisation, 2) Water temperature is controlled. Temperature fluc-
while too many sperm may result in embryonic abnor- tuations reduce survival and temperature affects
malities through polyspermy (section 6.3.4). development rate.
24.4.2.3 Triploidy 3) Larvae are kept at low densities, 1–5 larvae/mL, in
Triploidy is induced in bivalve eggs by blocking the first large farming volumes, often 10–20 000 L (Figure 3.8).
or second meiotic division preventing the release of The tanks are typically stocked with embryos at a
either the first or second polar body, respectively level that is several times greater than the anticipated
(section 7.8.2). In either case the result is a diploid egg final density of larvae. Density is reduced during
nucleus which becomes a triploid nucleus once it is larval development by mortality and discarding the
fertilised by a haploid sperm nucleus. There are various slower‐growing individuals during the regular sieving
chemical and physical methods for accomplishing this program (see 7. below).
process in bivalves (Gosling, 2003). The most reliable
method is by crossing tetraploids and diploids, using 4) With a final density of about 1 larva/mL, a 20 000 L
tetraploid broodstock. Thus, lines of tetraploid Pacific tank has an output of 20 million pediveligers.
oysters have been developed for large‐scale production
5) Mass‐cultured unicellular algae are added as food
for the larvae. Usually a mixture of species is
supplied, because mixed species diets give a better
balance of nutrients (section 9.2.4). Small unicellular
algae, about 5 μm, are used, such as Isochrysis
558 Aquaculture American cupped oyster (Crassostrea virginica) are sent
from hatcheries to distant oyster farms in the USA
s pecies, Pavlova species, and single‐celled diatoms, (‘remote setting’). The pediveligers are settled at the
Chaetoceros species (Table 9.2). Long‐chain, spiny recipient farms.
diatoms, which are appropriate to the setal feeding
structures of crustacean larvae, are quite unsuitable 24.4.2.7 Culchless Spat
for the ciliary feeding mechanisms of bivalve larvae. A technique used in settling cupped oyster larvae is to
6) Gentle aeration is used to maintain water movement, provide particles of shell, about 500 μm diameter, as sub-
keeping the larvae in suspension. strates. The pediveligers settle and metamorphose on
7) Culture water is changed regularly to control the these, but within a few days the spat shells have grown
build‐up of metabolites from larvae and algae, and larger than the particles on which they settled. The shell
especially the build‐up of bacterial populations. The particles with and without spat are then passed through
culture water and larvae are discharged through an appropriate sieve that separates the spat from the
sieves of appropriate mesh size to collect the larvae plain particles. These spat have immediate advantages
(Figure 3.9). The water may be discharged through for subsequent culchless grow‐out.
several sieves of different mesh sizes, with the larg-
est mesh uppermost, to grade the larvae. Abnormally 24.4.3 Nursery Farming
small larvae pass through the sieves and are lost in Early bivalve spat are 200–500 μm in shell length and
the effluent water. The larvae retained on different very vulnerable to predation and overgrowth by fouling
mesh sizes are transferred to clean tanks with the organisms. They need good concentrations of POM to
objective of having uniform batches of larvae. sustain their growth. Thus, best survival and growth of
Sieving the water flowing out of a 20 000 L tank may hatchery‐produced spat may be obtained by maintaining
be accomplished in an hour with the water rushing them in on‐shore facilities with cultured microalgae as
through the sieves. Yet, surprisingly, the thin shells food. The spat may be maintained in a flow‐through sys-
of the veligers and pediveligers survive this tem with high POM content or within a recirculating
treatment. system with supplementary microalgae. In the latter
8) As in hatcheries for other kinds of aquacultured ani- case, the spat may be held on sieves at high densities with
mals, scrupulous attention is paid to cleanliness to either vigorous up‐welling or down‐welling flows
avoid contamination and bacterial blooms in the through the sieves. Up‐welling has the advantage of lift-
bivalve larvae tanks. There is generally a separate lar- ing the spat off the mesh and stirring them; while down‐
val culture or tank room with limited access. The welling packs them down onto the mesh. Stronger flows,
inner surfaces of larval culture tanks are scrubbed however, can be used with down‐welling systems. The
with hypochlorite solution to sterilise them, or with mass‐cultured microalgae added to the recirculation sys-
detergent, between uses. Sieves, hoses, buckets, etc., tem does not need to be as ‘clean’ as those used for larval
are similarly sterilised between uses. culture and may be cultured in open tanks.
24.4.2.5 Settlement When the spat are of sufficient size they are transferred
Late pediveliger larvae may be sieved from their culture to off‐shore sites for ocean‐nursery farming. There is
water on an appropriate‐sized mesh and transferred to pressure to make this transition as early as possible as it
settlement tanks with static water and settlement‐induc- is costly to maintain the spat in an on‐shore facility with
ing substrates. Alternatively, appropriate substrates may feeding and maintenance.
be added to the larval tanks. Oysters, scallops, clams and
pearl oysters have their individual requirements for set- 24.4.4 Ocean‐nursery and Grow‐out
tlement‐inducing substrates in the hatchery, as they have Various methods are used for culturing bivalves during
in the field. Chemicals may be added to the water in their ocean phase. These reflect differences in the biol-
hatcheries to promote settlement and metamorphosis, ogy and preferred habitat of the farmed species; local
e.g., epinephrine (adrenalin) at 100 μM/L and GABA factors such as labour and material costs; and market
(γ‐amino‐butyric acid) may be used. price. A fundamental difference is between culturing
bivalves:
24.4.2.6 Remote Settling ●● within the seabed;
In the final stages before settlement, oyster pediveligers ●● on or just above the seabed (Figure 24.9); or
are amazingly robust and can be collected into dense ●● near the ocean surface.
balls of millions of larvae, wrapped in damp material
and stored in a refrigerator or freighted in small con-
tainers. In this way pediveligers may be transported over
long distances by airfreight, e.g., pediveligers of the
Bivalve Molluscs 559
Figure 24.9 Intertidal farming of oysters in open, above‐substrate trays in the Georges River, New South Wales. Source: CSIRO
ScienceImage 2497 Oyster. Reproduced under the terms of the Creative Commons Attribution Share Alike License CC-BY-SA-3.0.
24.4.4.1 Within Particulate Seabeds Mesh boxes are used for small bivalves, especially
The bottom‐inhabiting cockles, clams, etc. are reared cultchless oysters immediately after transfer from the
within natural muddy to sandy seabeds with minimal land nursery. Later, the oysters are transferred to open
intervention. In some cases, the seabed may be prepared mesh baskets or trays when they are less prone to
for the addition of seed bivalves by ponding and fertilisa- p redation (Figure 24.9). Horizontal batons are also used
tion or by harrowing to loosen it and remove predators where batons were previously used to collect spat from
such as starfish. After seeding, the surface of the farming natural spatfall.
area may be covered with a mesh to deter predators and
the area may be defined with a fence. 24.4.4.3 Surface or Suspended Farming
Farming methods at the surface include hanging the
24.4.4.2 On or Just above the Seabed bivalves on ropes or in appropriate farming units from
Typically this is farming at appropriate levels in the inter- rafts, longlines and floats.
tidal zone with bivalves that tolerate regular aerial expo- ●● Rafts are rectangular metal, wooden or bamboo frames
sure. The advantages of intertidal culturing are outlined
in section 24.5.2. with buoyancy provided by large air‐filled drums or
floats (Figure 3.7). Ropes with bivalves attached hang
Some bivalves are farmed on the surfaces of hard sub- down at intervals from cross‐members on the raft. In
strates, such as cement slabs, and horizontal and vertical raft farming, the bivalves are typically mussels attached
stakes, which require natural spatfall. Rows of horizontal to vertical ropes in vast numbers (Figure 24.10).
or vertical stakes (usually wood or bamboo) are used for ●● Longlines are 50+ m horizontal ropes, supported at
oyster and mussel farming. Bivalves are also farmed on the surface by floats at regular intervals. Bivalves are
racks above the seabed in mesh boxes, mesh baskets, farmed on ropes suspended vertically at regular
trays, and horizontal wooden and fibre‐cement batons.
560 Aquaculture
Figure 24.10 Raft with numerous vertical
ropes with mussels attached. Carrick
Roads, Cornwall, England. Source: Eva
Crocker. Reproduced under the terms of
the Creative Commons Attribution Share
Alike License CC-BY-SA-3.0.
intervals along the longline. Attached to the vertical hatchery through the long period to sexual maturity.
ropes are various farming structures depending on the However, as well as chromosomal manipulations
farming species in particular (Figures 2.14 and 24.11). (section 24.4.2.3), there have been selective breeding
These include: programs with bivalves (Gosling, 2003). These have
●● lantern nets (elongate cylindrical nets with regular involved the usual procedures of individual selection,
horizontal partitions on which scallops are kept), family selection and within‐family selection. There
●● ropes packed with mussels are major breeding programs, especially with oysters.
●● ‘ear‐hung’ pearl oysters and scallops The programs have mainly targeted disease‐resistance,
●● vertical series of pyramid shaped nets although growth rate has also been considered
Longlines are held in place at their ends by terminal (Table 7.3). Despite successful results from research
anchors or attachment to points of hard substrate below. programs, it seems to date that there are no bivalve
Some longlines have their supporting floats held below industries that are substantially based on selected strains
the surface by anchors, so that they may be invisible at supplied from hatcheries.
the surface or only indicated by marker buoys. This sys-
tem has the advantages of being more resistant to storm 24.5 Farming Problems
damage, having less chance of damage from boating,
being less conspicuous to poachers, and being more 24.5.1 Predators, Parasites and Diseases
a esthetically acceptable. 24.5.1.1 Predators
Floats are single versions of the multi‐float longline There are numerous species of bivalve predators and
system. The buoyancy floats are much larger and directly these must be taken into account in successful field‐
support the farming structure below. They are employed based farming of bivalves, especially during the early
in similar ways to longlines in that they are often joined months of development while their shells are fragile.
in lines. ●● Gastropod predators feed using a toothed rasping rad-
24.4.5 Breeding Programs ula, in an extensible proboscis. They either drill
There is a fundamental problem for selective breeding through one shell of the bivalve to access the animal
programs with invertebrates that shed vast numbers of within or push their proboscis between the prey’s
gametes into the environment. The progeny from the valves. The major gastropod predators of bivalves
selected broodstock are dispersed among the natural include members of the families Naticidae (moon-
population and not identifiable. Thus, the progeny of snails), Ranellidae (triton shells), Buccinidae (whelks)
successive selected generations must be retained in the and Muricidae (murex shells).
Various nets hung from longlines Bivalve Molluscs 561
Pearl net Box net
Lantern net
a = Pearl net
d = Box net
c = Lantern net
b = Circle net Circle net Pocket nets
Sandwich net
e = Openable sandwich net f = Pocket net with frame g = Pocket net without frame
Figure 24.11 The variety of nets used for culturing bivalves. These are suspended from long‐lines or from floats. Source: Gervis and Sims.
1992. The Biology and Culture of Pearl Oysters. ICLARM Stud. Rev.21. Reproduced with permission.
●● Crabs, which include swimming crabs (Family ●● A variety of rays and fishes have been reported to feed
Portunidae), rock crabs (Families Cancridae and on farmed bivalves. The fish include flatfish and whit-
Grapsidae) and stone crabs (Family Xanthidae), feed ing (active on soft seabeds), perch, bream, puffer fish,
on bivalves. Crabs are equipped with two chelate arms and snapper. These fish are bottom feeders that both
(’pincers’): the larger chela being used for crushing and crush and consume the whole prey or crop the siphons
the smaller for manipulating and picking. Other off burrowing bivalves. The latter activity is not neces-
decapod crustaceans, such as hermit crabs, shrimp sarily lethal to the prey but must reduce its growth rate.
and snapping prawns, while not equipped with such
powerful crushers, will readily consume soft‐shelled Measures against predators include excluding them with
juvenile bivalves.; appropriate‐sized meshes. There is, however, a problem
in that meshes can be fouled by algae and epifauna, seri-
●● Starfish (seastar) predators are mainly a problem in ously reducing the flow of water to these filter feeders.
temperate regions. They particularly feed on bivalves Another measure is to farm the bivalves away from the
that inhabit soft‐seabeds: flat oysters, clams, cockles predators’ habitats (e.g., above the bottom or suspended
and scallops. The starfish attaches to both valves with from the surface), and regularly inspect for mortality and
its tube feet, pulling the valves apart with prolonged identification of its source (e.g., damaged mesh, con-
tension, and then inserting its extruded stomach cealed predatory gastropods). Predators, however, may
between the valves. get around all these measures to exclude them by settling
from the plankton as larvae onto the farming equipment.
●● Octopuses have not been widely reported as predators They may then have sufficient time to grow to a size
of farmed bivalves, but they prey on bivalves through where they become significant predators.
prolonged tension in a similar manner to starfish.
562 Aquaculture spat collectors before settlement reduces the sites for
pediveligers to settle and metamorphose. The initial
24.5.1.2 Parasites and Diseases phase of biofouling by bacteria and diatoms may result in
Chapters 10 and 11 describe some of the diseases and a slimy coating that is unattractive to the settling pedive-
parasites of bivalves. The parasitic and other disease‐ ligers of many species. Furthermore, spat and small juve-
causing organisms of bivalves include many of the kinds nile bivalves are particularly vulnerable to biofouling
of organisms that oppress other aquatic invertebrates: overgrowth due to the relative size of macroscopic foul-
●● herpes‐like viruses and Rickettsia; ing organisms.
●● eubacteria (e.g., Vibrio species);
●● protozoans (e.g., Perkinsus marinus); A further aspect of biofouling of suspended farming
●● fungi, sponges and polychaete worms, (which pene- systems, e.g., longlines and rafts, is that it can add so
much weight and drag to the system that it threatens the
trate the shell and make it more prone to crushing by system’s buoyancy and stability in rough weather.
predators);
●● flat, tape, nemertean and nematode worms; Some bivalves are subject to biofouling through their
●● pyramidellid gastropods (ectoparasites which suck shells. These fouling organisms include boring fungi,
body fluids) (Figure 10.4); sponges and tube worms that may riddle the bivalves’
●● endoparasitic copepods; and shells. The borers may penetrate through the inner
●● pea crabs (‘food‐stealers’ amongst the gills in the nacreous layer of the shell, necessitating the mantle to
m antle cavity). secrete new nacreous layers to keep the borers at bay.
Some, such as copepods and pea crabs, may have a Borers weaken the shell, making the bivalve more prone
m inimal effect on the host: causing some loss of host to crushing predators, and their burrows detract from
condition due to loss of nutrients and local irritation. the shell’s appearance. This is particularly a problem for
Others, such as some viral and protozoan diseases, pearl oyster farming where good quality shells are
can have devastating effects on bivalve aquaculture v aluable. In the Australian cultured pearl industry such
industries, through mass mortalities, resulting in the riddled shells are known as ‘chicken shell’.
industries becoming uneconomic, being closed down or
requiring alternative more‐resistant species. The tradi- One of the simplest ways to control biofouling is to
tional flat oyster (Ostrea edulis) industry in France is an expose the farmed bivalves and their fouled equipment
example of the last case. The Pacific oyster was imported to air and sunlight for a sufficient period to kill most of
because of its resistance to two protozoan parasites that the fouling organisms without killing the bivalves. This
were causing havoc with the native flat oyster. Proportions relies on the ability of bivalves for sustained closure of
of oyster species in the annual harvests varied, but in their valves, avoiding desiccation.
1984, a particularly bad year for the native oyster, the
annual harvest was 98% Pacific oysters (Figure 24.15). As previously explained, culturing in the intertidal
zone has the advantage that exposure to air occurs regu-
24.5.2 Biofouling larly without movements of stock and generally biofoul-
Like boat hulls and jetty piles, aquaculture structures ing is less of a problem in intertidal farming than in
become coated with fouling organisms, which may subtidal farming. However, intertidal farming is not a
include communities of bivalves that are not the target guarantee against fouling of fine meshes (Figure 24.12):
species (Fitridge et al., 2012). It is a particular problem regular maintenance may still be needed to remove
for bivalve farming as it restricts water flow to these filter fouling.
feeders. Furthermore, many of the fouling organisms are
themselves filter feeders and compete for available POM Methods for controlling biofouling include pressure
and DO with the farming species. They include bacteria hoses and mechanical scrubbers. As well as these physi-
and diatoms, macroalgae, sponges, hydroids, hard and cal methods of biofouling control, chemical and biologi-
soft corals, bryozoans, tube‐inhabiting polychaetes, cal methods may be used. Most of these chemical
barnacles, mussels (feral species), and tunicates. A sur- methods, as with exposure to air, rely on the bivalves’
rounding mass of fouling organisms may have a greater capacity to close valves and shut out deleterious environ-
filtration rate and oxygen consumption than the farmed mental factors for some time. The fouled bivalves may be
bivalves, creating a low food and DO environment for immersed for appropriate periods in freshwater or
them. Thus, regular removal of biofouling results in hypersaline seawater. Toxic solutions such as hypochlo-
more rapid growth in the farmed bivalves. rite may also be used. Other antifouling chemicals may
be used to treat the farming equipment. These chemicals
The problems of biofouling may be acute during the include tar, some new synthetic organic coatings, and, in
spatfall and seed stages of bivalve farming. Biofouling of the past, toxic paints containing copper, zinc or tin.
Tributyl tin, in particular, was a very successful and
widely used antifoulant. However, use of these toxic
m etals as antifoulants is now recognised as being
Bivalve Molluscs 563
150
Annual oyster production (103 t ) 100
Crassostrea gigas
50
Ostrea edulis
0 1960 1970 1980 1990 2000 2010
1950
Figure 24.12 Fluctuations in the annual harvests of Ostrea edulis and Crassostrea gigas in France from 1950–2014. FAO (2016) Data.
Source: Reproduced with permission from John Lucas.
environmentally unacceptable (section 3.4.2). Further often known as red tides. During red tides the harvesting
more, they may cause abnormalities and deaths of and consumption of bivalves may be suspended due to
farmed bivalves, and the metals can accumulate in biotoxins accumulating in the bivalves from filter feeding
bivalve tissues to levels unacceptable for human on toxic phytoplankters. More insidiously, at other local-
consumption. ities there are blooms of toxic phytoplankters without
obvious discolouration of the water.
Biological methods are appropriate where there are
one or a few major fouling organisms to deal with. The Most sources of these biotoxins are dinoflagellates and
breeding season, patterns of larval settlement, and about 20 out of the total 1500 dinoflagellate species have
life cycle of the fouling organism must be known. been implicated. They include species of Alexandrium,
For example, knowing the breeding period of the fouling Dinophysis, Gymnodinium and Porocentrum. Several
organism, it may be appropriate to put out alternative species of the diatom Nitzschia are also toxic.
attractive substitutes for their larval settlement; or it may
be appropriate to use a chemical or exposure treatment Some of these blooms are lethal to the bivalves, c ausing
while the fouling organisms are recently settled and more mass mortality on bivalve farms. It appears, however,
vulnerable. Local areas of heavy settlement of fouling that biotoxins do not necessarily poison bivalves. Dense
organism larvae may be avoided or just avoided during phytoplankton blooms may instead cause mass mortali-
the period of settlement. If the fouling organism larvae ties by choking the bivalves’ filter‐feeding and respira-
tend to settle at particular depths, then these can be tory mechanisms, and by causing very low DO levels in
avoided in suspended farming. the environment.
24.5.3 Biotoxins and Gut Contents Where biotoxins are ingested and assimilated, they
24.5.3.1 Biotoxins accumulate in the bivalves’ digestive gland and other
The content of this section may seem to discourage organs. The biotoxins may subsequently affect humans
bivalve consumption for some readers, but it must be who consume the infected molluscs. Some of the sources
remembered that bivalves constitute a huge proportion and effects of biotoxins from bivalves are shown in
of aquaculture production and biotoxins are rarely Table 24.2.
encountered.
The biotoxins have severely affected bivalve farming
Some phytoplankton species bloom to cell densities of industries through industry closures or loss of consumer
millions/mL under appropriate hydrological conditions. confidence. Furthermore, while biotoxins in bivalves
The blooms discolour inshore waters: a phenomenon have been a long‐standing problem for the bivalve farm-
ing industries of Europe, SE Asia and North America, the
problem seems to have become more common and
widespread.
564 Aquaculture
Table 24.2 Bivalve biotoxins and the medical conditions that they cause.
Poisoning Condition Biotoxin Sources
Amnesic shellfish (ASP) domoic acid
Diarrhoeic shellfish (DSP) gastro‐intestinala, okadaic acid Diatoms:
Neurotoxic shellfish (NSP) neurologicalb polyether toxin Nitzschia species
Paralytic shellfish (PSP) gastro‐intestinal, complexes of toxins Dinoflagellates:
neurologicalb Dinophysis species
neurologicalb Dinoflagellate
Gymnodinium brevi
neurologicalc Dinoflagellates (including)
Gymnodinium catenatum
a lower level = nausea, abdominal cramps and diarrhoea.
b more severe = headaches, dizziness, disorientation.
c lower level = numbness, more severe = muscular paralysis, breathing difficulties.
Suggestions for this are: a nimals to purified seawater for several days while they
●● increased scientific awareness of the problem; clear their gut contents: a process called depuration.
●● increased utilisation of coastal waters for aquaculture; In many areas, depuration is used as a routine practice
●● increased algal blooms due to eutrophication of coastal between harvesting and marketing.
waters; 24.6 Introductions and Other
●● unusual climatic conditions stimulating algal blooms; Environmental Issues
●● transport of dinoflagellate cysts in ships’ ballast
24.6.1 Introductions
water; and The hazards of introductions are applicable to bivalves.
●● transport through transfers of bivalve stocks.
Bivalves that are infected with biotoxins don’t remain While the Pacific oyster has been introduced over
infected indefinitely. For instance, the safe level for PSP is large distances from its original distribution, appar-
0.8 ppm shellfish tissue (80 μg/100 g). However, although ently without adverse environmental effects, this must
toxins in infected bivalves may be magnitudes above safe not be taken as support for introductions. There are
levels, after the toxic algal bloom clears from their envi- particular temptations with bivalves as translocations
ronment the animals lose their accumulated toxins over and introductions are relatively simple because many
periods of weeks or months and become marketable. bivalves tolerate extensive periods out of water or in
confined water if handled correctly. However, the
The safest, but uneconomical, way to cope with bio- hazards of prevalent diseases, associated noxious
toxins in bivalves is to bioassay all suspect product before organisms, genetic impacts and potential to be a pest
it is marketed. Practical solutions are to have annual are all applicable to bivalves.
periods of closure in areas of long‐standing bivalve farm-
ing where the occurrence of toxic algal blooms is regular Even the introductions of the Pacific oyster have not
and seasonal. been an unmitigated success. The Pacific oyster was
introduced to Tasmania in 1970s and is now the basis of
24.5.3.2 Gut Contents industries in Tasmania and South Australia. It has
The other possible sources of health problems for bivalve spread, however, up the eastern coast of Australia to
consumers are live micro‐organisms in bivalves’ guts where there is an industry for the Sydney rock oyster,
when the animals are consumed raw. Bivalve guts con- Saccostrea glomerata. The Sydney rock oyster is a spe-
tain bacteria and viruses, which they have ingested cialty ’boutique’ oyster that commands a high price and
through their filter feeding. Coastal waters may have some farmers don’t welcome the invading Pacific
substantial levels of faecal bacteria and viruses in the oyster.
water column and hence in the bivalves’ guts. The bacte-
ria include Escherichia coli, which can cause gastroen- The zebra mussel is a well‐known and more extreme
teritis and typhoid fever. example of a bivalve introduction. It seems that it was an
unwitting introduction into the Great Lakes system,
These micro‐organisms in the bivalves’ guts can be North America, in the mid‐1980s, probably from ballast
dealt with much more readily than biotoxins accumu-
lated in their tissues. It is a matter of exposing the
water of a trans‐Atlantic ship or ships. It has become a Bivalve Molluscs 565
disastrous fouling organism in this environment with
both ecological and economic impacts (Connelly et al., 24.7 Industry Reviews
2007). Furthermore, it has the potential to cause the
extinction of some endemic freshwater mussel species. It 24.7.1 Oysters
has eliminated most endemic freshwater mussel popula- Oysters have long been regarded as a seafood delicacy
tions within the lower Great Lakes. and farming methods are long established (reviewed by
Matthiessen, 2001).
24.6.2 Environmental Issues
One potential environmental problem with many As considered earlier, by far the greatest proportion of
a quaculture operations, the input of large quantities of global oyster production is from cupped oysters, with
nitrogen‐rich feeds, is not present in bivalve aquacul- the Pacific oyster being pre‐eminent (Table 24.1). The
ture. There may be artificial feeding of bivalve larvae Pacific cupped oyster is farmed around the globe in more
and early juveniles in hatcheries, but this is only with than 30 countries. Its growth rates, favourable shape for
relatively small biomasses of bivalves and they are fed marketing and relative resistance to disease compared to
live microalgae. By the time the farmed bivalves reach a other cupped oysters and especially compared to flat
substantial size they are totally dependent on natural o ysters, make it very attractive for farming.
phytoplankton. There can, however, be deleterious envi-
ronmental effects from the filter feeding. Large marine There are about 11 other species of cupped oyster
mussels may each filter 2–5 L/hr. In very general approx- farmed locally around the world. Farming of five species
imation, a raft of mussels may filter 70 million L/day, of flat oysters, despite their relatively high value is mini-
ingest 180 t of organic matter/yr and produce 100 t of mal compared with cupped oysters. In particular their
pseudofaeces and faeces/yr. The ‘rain’ of faeces and propensity for diseases discourages farming.
pseudofaeces from these rafts endangers the benthic
environment below. It may transform the seabed below Oysters are farmed on the bottom, off the bottom and
into anaerobic conditions, just as this may occur below suspended from the surface. The spat may be obtained
cages in fish farming with the ‘rain’ of uneaten feed and from natural settlement on culch, e.g., sticks, shells and
faeces. The solutions are: tiles (Figures 24.7 and 24.8), or they may be hatchery
●● locate the farming structures in regions of high produced (Figure 24.13). The spat may be left on culch or
they may be removed. The simplest level of farming is
current velocity to promote dispersal of faeces and with natural spat in areas of firm substrate. These oyster
pseudofaeces in the water column farms are usually fenced off, predators are controlled,
●● limit biomass/unit area of farmed bivalves to a level and other management measures undertaken. Harvesting
where dispersal processes are sufficient to minimise is often by dredge. Stick culch with seed oysters may be
faecal and pseudofaecal accumulation on the seabed placed horizontally on racks above the seabed or driven
●● regularly move rafts and longlines to new sites before vertically into the seabed. Culchless oysters and oysters
there is excessive accumulation of wastes on the sea- on small pieces of culch may be kept in trays or mesh
bed below containers on racks above the seabed (Figure 24.9) or
Cleaning the biofouling growths off the bivalves’ shells suspended from the surface from longlines or rafts
and farming apparatus may also be a source of environ- (Figures 24.10 and 27.10).
mental problems where the biofouling debris is discarded
into the adjacent water. Oyster fisheries and farming industries have been
A different kind of environmental problem arises characterised by great fluctuations in annual production.
because bivalves are usually farmed in coastal regions Factors causing these fluctuations are:
where there are other users of the environment. As with
other aquaculture operations in these regions, farms ●● over‐exploitation to the extent of reducing the repro-
consisting of rafts, racks, longlines and floats may be ductive output of field populations and subsequent
perceived to be an environmental problem from an recruitment of spat;
aesthetic, navigational or recreational viewpoint. On the
other hand, there may be situations where bivalves can ●● mass mortalities from various protozoan and viral
be used with positive environmental effects, such as diseases, sometimes resulting from overstocking or
removing particles and nutrients from pond effluent introduced pathogens; and
(Jones et al., 2001).
●● mass mortalities from unusual environmental condi-
tions, including temperature extremes, low salinities
and red tides.
Figure 24.14 gives an excellent example of wide f luctuations
in annual oyster harvests from a farming industry.
The Sydney rock oyster industry in eastern Australia
is an example of fluctuating fortunes. The industry
commenced mainly in southern Queensland during
566 Aquaculture
Figure 24.13 Oyster farming at Bretteville‐sur‐Ay, Manche Department, Normandy. Source: Southgate et al., 2016. Reproduced with
permission from Journal of Shellfish Research.
Figure 24.14 Crassostrea gigas oyster
spat. Scientists at CSIRO Marine Research
are using DNA‐marker‐assisted selection
to improve the qualities of Pacific oysters.
Source: CSIRO ScienceImage 2775 Oyster
Spat. Reproduced under the terms of the
Creative Commons Attribution Share Alike
License CC-BY-SA-3.0.
the late nineteenth century with a simple system of the industry in southern Queensland and northern New
o yster banks. The flourishing industry, however, crashed South Wales (Latitude 28°S). In southern New South
through massive losses of oysters with QX disease Wales (Latitude 38°S), the oysters suffer `winter
(caused by a protozoan parasite, Marteilia sydneyi, mortality’ (caused by another protozoan parasite,
s ection 10.5.1.1). QX continues to be a problem limiting Mikrocytos roughleyi).
24.7.2 Clams and Cockles Bivalve Molluscs 567
Some clams and cockles are the basis for large aquacul-
ture industries that are often very simple and traditional wide range of farming periods. Clams and cockles are
in technology, e.g., the farming industries for blood generally slow growers and periods of 2+ years to
cockles, Anadara species (Table 24.1). They may consist commercial size are common in the larger species.
of little more than collecting seed from areas of heavy This adds to the necessity for low cost technology in
natural settlement and then stocking the seed at appro- the grow‐out phase.
priate densities, e.g., 10 million/ha, in defined farm areas
where there are favourable conditions for growth and Reference has been made to the most unusual group
predator control. of clams, the giant clams. These have been the target
of much farming‐oriented research in recent decades.
Many clam industries are based on hatchery and nurs- The greatest success has been for the ornamental
ery technology. For example, the hard clam or northern a quarium trade (Section 26.5.3).
quahog, Mercenaria mercenaria, industry of eastern
North America cultures the larvae and spat using similar 27.7.3 Mussels
hatchery methods and upweller systems to those The highest productivity of bivalve farming per unit
employed in oyster farming. Then the seed clams are farm area has been reported for marine mussels. These
transferred to the field at densities of 3000–4000/m2 into mussel farms operate in the western Galicia region of
carefully prepared seabed areas, floating trays or trays on Spain in a series of sunken river valleys (rias). Primary
racks. After a year, when the juveniles reach about 25 mm productivity in the rias was found to average 10.5 μg
shell length, they are spread out in the grow‐out area. organic carbon/L/hr over the year due to upwelling of
With these techniques the aquaculture production of the cold nutrient‐rich water and runoff from the adjacent
hard clams in the USA amounted to 28.4 thousand t in hills. These provide copious phytoplankton for mussel
2014. This quantity, however, is very small compared to farming, resulting in very high levels of mussel produc-
the total of 5.36 million t global production of clams, tion from dense rafts (Figure 24.15). Interestingly, annual
cockles and arkshells, etc., which is based on >40 species production has been quite variable: ranging from 142
of farmed bivalves in this category. thousand t to 261thousand t over the period 1994–2014.
It is now taking longer in the central regions of the rias
With a great variety of species, growth rates and com- for the mussels to reach commercial size, apparently due
mercial sizes within this group, there is necessarily a to excess raft density reducing phytoplankton levels.
Figure 24.15 A cluster of mussel rafts in the Ria of Muros, Galicia, Spain. Source: Ramon Pineiro. Reproduced under the terms of the
Creative Commons Attribution Share Alike License CC-BY-SA-3.0.
568 Aquaculture
Table 24.3 Details of some marine mussel mariculture industries. Blue mussel = Mytilus edulis. Chinese
mussel = Mytilus coruscus. Green mussel = Perna viridis. Mediterranean mussel = Mytilus galloprovincialis.
New Zealand mussel = Perna canaliculus.
Country Mussel species Main farming techniques
China Blue, green, Chinese, etc. Various
Spain Blue Rafts
Italy Mediterranean Vertical poles
Thailand Green Vertical poles
France Blue and Mediterranean Vertical poles (‘bouchets’)
Netherlands Blue Seabed
New Zealand New Zealand Longlines
Germany Blue Seabed
Philippines Green Vertical poles
As well as raft farming, mussels of both Mytilus and seed scallops are 10–15 mm they are removed from the
Perna species are grown in seabed farming, on vertical collectors and placed in pyramid‐shaped mesh nets
poles in the intertidal zone and in longline farming suspended from longlines or rafts. Juvenile scallops, 30
(Table 24.3). mm, may then either be:
24.7.4 Scallops ●● placed into suspended lantern nets (Figure 24.11);
Hardy (2006) gives a comprehensive treatment of the ●● ‘ear hung’, whereby a small hole is drilled through the
various phases and aspects of scallop farming, including
business and marketing aspects. hinge ‘ear’ of the shells and the scallops are tied to
supporting ropes; and
The scallop’s large adductor muscle is a highly valued ●● released to prepared regions of the marine substrate.
seafood and they have been subject to heavy fishing
in many regions. However, scallop fisheries are often The first two methods are more expensive due to labour
unpredictable and over‐exploited, so farming is an and equipment costs.
attractive alternative to fisheries. Despite the interest
in farming, global aquaculture production of scallops The third method is cheaper but results in greater
is almost exclusively from China and Japan. They pro- mortality. Scallops are generally farmed on the marine
duced 1.6 million t and 167 thousandt, respectively, in substrate on two scales. One is in small‐scale enclosures;
2013: mainly culturing the large and high prized yesso the other is on a large scale without enclosures (Hardy,
scallop (Pecten yessoensis), which has a harvest size of > 2006). Small‐scale enclosures, corrals, are tens of square
100 mm shell length. metres in size, and require diving to maintain the equip-
ment and harvest the scallops. Enclosure walls act as
Interestingly, at least in the past, the technology for barriers to loose seaweed drifting along the seabed. They
culturing scallops contrasted between Japan and China can become heavily fouled, reducing water flow through
in a way that one would not necessarily have predicted. the enclosure and requiring clearing. Coralls must be
The Japanese industry, which tends toward hatchery seeded with juvenile scallops of sufficient size to mini-
production as a rule, relied on collecting bountiful natu- mise predation by shell crushers. They are seeded with
ral spat; while China had a large number of hatcheries. up to 12 scallops/m2.
The yesso scallop is a cold‐water species and most Large‐scale farming operations involve areas of tens
Japanese production is from northern Japan. While nat- of square kilometres. The seabed may be initially
ural spatfall is used, it is not a casual operation. The dredged to remove predators such as starfish and large
reproductive state of scallop populations and progress of crabs. The area is seeded with millions of scallop spat of
natural larval development are carefully monitored to appropriate size. After the growing period to commer-
accurately time the deployment of spat collectors in each cial size, 2+ years, the scallops are harvested by
region. The spat collectors (mesh bags with internal d redging. Thus, there is a 2+ year rotation of the farmed
mesh) are hung from sub‐surface longlines. When the area. As noted above, there may be substantial mortal-
ity, >50%, but this is offset by the low cost of husbandry
and equipment.
24.7.5 Pearl Mussels Bivalve Molluscs 569
Pearls occur very occasionally in many bivalves including
table oysters and there is a common misconception that Figure 24.16 ‘Boutique’ freshwater pearls that have been cultured
pearls result from sand or other particles lodging within to produce shapes for this necklace style. Source: Reproduced with
the bivalve’s mantle cavity. The resulting irritation causes permission from John Lucas.
the bivalve to coat the loose particle with its nacreous
shell layer. In fact, the water current through a bivalve’s The Chinese aquaculturists who produce pearls from
mantle cavity is strong enough to expel loose particles. It freshwater mussels are often additionally engaged in
is more likely that the irritation is from damage to the agriculture and aquaculture of freshwater fish.
mantle tissue from a small intruder, such as a crab or gas- 24.7.6 Pearl Oysters
tropod, pieces of broken shell or sharp particles lodged There is a comprehensive treatment of the biology and
in place, or small embedded parasites. ecology of pearl oysters, and the processes and economics
of cultured pearl production (Southgate and Lucas, 2008).
The natural pearls from most bivalves are not glossy,
reflecting the plain surface of the inner nacre layer. William Saville‐Kent, Commissioner of Fisheries for
However, the glossy nacre layer of pearl mussels and Queensland is attributed with developing the technique
pearl oysters results in glossy pearls. These are usually for cultured pearl production from pearl oysters.
small and irregular, and are infrequent. Thus, techniques A Japanese entrepreneur, Kokichi Mikimoto, was subse-
have been developed to produce commercial numbers of quently responsible for developing the cultured pearl
improved pearls. industry and gaining acceptance of cultured pearls.
Cultured pearls from large freshwater mussels, such as A spherical bead made typically from Mississippi mud
Hyriopsis cumingii, are produced mainly in China. The oyster shell is used as the ’nucleus’ for the cultured pearl.
mussels occur in lakes and rivers. They are collected and The bead, which must be of an appropriate size for the
cleaned, and then pieces of mantle tissue are cut from a size of the oyster, is inserted into a pocket cut in the oys-
donor mussel. These are inserted into small wounds cut ter’s gonad (Figure 24.17). Inserted with the bead is a
in a recipient mussel’s mantle. The cells from the donor small piece of outer mantle tissue removed from a donor
tissue dissociate, migrate and reassociate to form a sac oyster. Cells of the transplanted mantle tissue spread
(a pearl sac), the inner surface of which secretes succes- over the bead surface to make a pearl sac and this secretes
sive layers of glossy nacre. Thus, the pearl consists successive layers of nacre onto the bead to make the cul-
entirely of nacre and is the product of the donor oyster’s tured pearl. Thus, cultured pearls are produced via host
cells and not the recipient host. Up to ca. 40 pieces of tis- oysters supporting foreign cells as for pearl mussels. The
sue may be inserted into the two mantle lobes of a large pearls, however, differ in composition between solid
host mussel. The impregnated mussels are farmed by nacre (mussels) and nacre coating a bead (oysters).
suspension in freshwater tanks with flow‐through or in
freshwater environments. The mussels are suspended The period between bead insertion into the pearl
in netting baskets or bags or suspended via holes through oyster and harvest varies between about 9 months and
their shells. The cultured pearls are harvested after 3 years with the thickness of nacre and quality of pearl
two to six years.
In the early stages of this industry, the resulting pearls
were <6 mm diameter and irregular (‘rice’ or ‘wrinkled’
pearls). Individually they had little worth, but their pro-
duction was reliable and large numbers were produced
per mussel. They were used in multi‐strand necklaces.
Furthermore, after the pearls had been harvested, the
long‐lived mussels could be returned to farming and
their pearl sacs would produce several further crops of
these nucleus‐free pearls.
Recent technological improvements are resulting in
larger and more spherical pearls which are approach-
ing the quality of those from pearl oysters and which
are considerably more valuable than the earlier fresh-
water pearls. Techniques have also been developed to
produce pearls of particular shapes and colours
(Figure 24.16).
570 Aquaculture 24.8 The Future of Bivalve
Aquaculture
Figure 24.17 A pearl‐seeding technician is attaching a half
spherical bead onto the inner shell of a pearl oyster for cultured Finally, some predictions for the future of bivalve
pearl production. The subsequent half‐pearl will be cut from the aquaculture:
shell and used for pendants, broaches, etc. Source: Reproduced ●● Bivalve industries will increasingly develop hatchery
with permission from Paul Southgate.
production of spat, instead of dependence on the
being directly related to this farming period. Only a small vagaries and limitations of natural spatfall.
percentage of the inserted beads result in high value ●● Genetics and stock selection will be researched and
pearls (Figure 2.15). Losses occur from oysters that die developed from the current limited basis. Increasingly,
from the insertion procedure, from ejected beads, and there will be industries based on hatchery‐produced
from other processes that affect the shape and surface seed stock reared from genetically‐selected brood-
quality. After the harvest, the pearls are graded before stock to have particular traits that make them more
being presented for sale. commercially viable.
●● There will be technological developments in the grow‐
Japan has traditionally been the largest source of out phase to increase efficiency and make better use of
pearls from pearl oysters, based on the Akoya oyster available sites.
(Pinctada fucata). The number of Japanese pearl farms ●● Bivalves will have a developing role in treating pond
peaked at >4000 in the 1960s and production of Akoya effluents, the water of large recirculation systems and
pearls peaked correspondingly at ca. 80 t/yr at that time. sea cage wastes through filtering suspended organic
The number of farms has since declined to ca. 1500 and and inorganic particles, and by absorbing dissolved
pearl production to ca. 25 t/yr. The decline in recent waste molecules.
decades is due to factors such as coastal pollution, toxic ●● While aquaculture in general will be very important in
phytoplankton blooms and disease. On the other hand, compensating for the limitations of terrestrial hus-
cultured pearl production has been increasing in bandry, bivalve aquaculture in particular has great
Australia, Indonesia and the Philippines (large silver‐ potential from its high productivity without feed
white pearls from P. maxima), in Polynesia (large black inputs and for its potential to be moved offshore into
pearls from P. margaritifera), and China (Akoya pearls). new oceanic environments (Duarte et al., 2009;
Simpson, 2011).
Similar techniques to those used for scallops in sus-
pended farming are used for pearl oysters, e.g., rafts or 24.9 Summary
long‐lines with suspended nets or mesh frames, or ’ear
hanging’ on ropes (Figures 2.14) according to location ●● Aquaculture of bivalves originated in antiquity with
and species. Sources of the pearl oysters for bead inser- basic techniques. It has continued through the ages
tion follow the lines of typical bivalve species: field col- increasing with the general increases in global aqua-
lection of appropriate‐sized oysters; spat from spat culture production in recent decades. Production from
collectors; hatchery‐reared juveniles. bivalve aquaculture has shown a mean annual rate of
7% increase over the period 2000–2014. As with fish,
crustaceans and seaweeds, China dominates bivalve
production and has been the major influence on their
increased aquaculture.
●● A significant advantage of bivalves for aquaculture is
that they filter‐feed on fine suspended particles with
their gills. Thus, they don’t require any additional feed
during their grow‐out phase. There is no need for fish-
meal and other protein sources. They substantially
feed at the first level of food webs (phytoplankton =>
bivalve) and thus capture a high proportion of the
energy of primary production
●● There are six major groups of cultured bivalves: clams, Bivalve Molluscs 571
oysters, mussels, scallops, freshwater pearl mussels and
pearl oysters. Techniques for farming them include sus- ●● Bivalves may be used in conjunction with other aqua-
pension from rafts and long‐lines, in trays on racks in culture to remove potentially polluting particulates,
the intertidal zone and in prepared soft substrates. One e.g., from effluent pond water or wastes in the vicinity
common feature is to minimise fouling and predation. of sea cages (they may then even be a second crop).
●● There is every reason to predict that bivalves will con- ●● Under appropriate conditions some bivalves can
tinue to be a major component of global aquaculture achieve levels of production/unit area that are not
production. Many species are regarded as premium matched by any free‐range domestic animal.
seafood and have high market demand. They have
excellent nutritional properties: bivalves are with tuna, ●● A picture of vigorous growth of bivalve industries is
salmon, sardines and other oily fishes in high n‐3 fatty not, however, completely honest. Bivalve industries
acid content. They may be reared with relatively sim- in some areas and regions are limited by disease,
ple techniques, although technological developments p ollution, biotoxins and availability of grow‐out sites.
will be needed for greater efficiency. These ongoing problems must be dealt with by
management and research.
References Jones, A. B., Dennison, W.C. and Preston, N. P. (2001)
Integrated treatment of shrimp effluent by sedimentation,
Connelly, N.A., O’Neill, C.R., Knuth, B.A. et al. (2007). oyster filtration and macroalgal absorption: a laboratory
Economic impacts of zebra mussels on drinking scale study. Aquaculture, 193, 155–178.
water treatment and electric power generation
facilities. Environmental Management, 40, Matthiessen, G. C. (2001) Oyster farming. Fishing News
105–112. Books. Blackwell Science, Oxford.
Duarte, C.M., Holmer, M., Olsen, Y. et al. (2009). Will the Simpson, S. (2011). The blue food revolution: making
oceans help feed humanity? BioScience 59, 967–976. aquaculture a sustainable food source. Scientific
American, 304, 54–61.
Fitridge, I., Dempster, T., Guenther, J. et al. (2012)
The impact and control of biofouling in marine Southgate, P.C. and J.S. Lucas (Eds) (2008) The Pearl
aquaculture: a review. Biofouling: The Journal of Oyster. Elsevier Press, Oxford.
Bioadhesion and Biofilm Research 28(7), 649–669.
Yukihira, H., Klumpp, D.W. and Lucas, J.S. (1999) Feeding
Gosling, E. (2003) Bivalve Molluscs: Biology, Ecology and adaptations of the pearl oysters, Pinctada margaritifera
farming. Fishing News Books, Blackwell, Oxford. and P. maxima to variations in natural particulates.
Marine Ecology Progress Series, 182, 161–173.
Hardy, D. (2006) Scallop Farming. 2nd edition. Blackwell
Science, Oxford.
573
25
Abalone
Peter Cook
CHAPTER MENU 25.6 Grow‐Out Systems, 580
25.1 Introduction, 573 25.7 Diseases and Parasites, 583
25.2 Production from Fisheries and Farms, 573 25.8 The World Abalone Market, 584
25.3 Biology, 576 25.9 Summary, 584
25.4 Culture Techniques, 577 References, 585
25.5 Postlarvae and Juveniles, 580
25.1 Introduction The various categories of abalone production referred
to in this chapter are based on those defined by Gordon
Abalone are large gastropod molluscs, belonging to the and Cook (2010) and include:
exclusively marine family, Haliotidae. Although abalone ●● abalone fisheries (the total legal allowable annual
have probably been exploited by coastal communities
since pre‐historic times, large scale commercial exploita- c ommercial catch);
tion has only been recorded since the early 1970s. Many ●● cultured abalone, which includes both the farming of
authors have suggested that there are about 75 species of
abalone worldwide, but in the most recent and authorita- abalone on land or in sea cages;
tive account of abalone taxonomy, Geiger and Owen ●● illegal catch (any harvest of abalone beyond total
(2012), recognised 56 valid species, with 18 additional
sub‐species. These authors did, however, suggest that the allowable annual fishing quotas).
detailed taxonomy is still somewhat uncertain. Of all of At the 9th International Abalone Symposium, held in
the species worldwide, less than one third are of com- Korea in October 2015, representatives of various
mercial importance, the others being either too small or countries were invited to present data on current aba-
too rare for commercial exploitation. A typical, commer- lone production in their region. This chapter presents a
cially exploited species, Haliotis midae, from South review of the information provided and also quotes
Africa, is illustrated in Figure 25.1. figures from published FAO statistics1. In all cases,
figures are adjusted to represent ‘in shell’ weight.
Abalone are found on shallow, sub‐tidal rocky shores
in most tropical and temperate waters, notable excep- 25.2 Production from Fisheries
tions being both polar regions, the east coast of north and Farms
America, and the west coast of the Indian subcontinent.
In most areas where abalone are common, they have Legal landings from abalone fisheries have gradually
formed the basis of important fisheries. Unfortunately, decreased from more than 27 000 t in the late 1960s to
however, in many cases, such fisheries have been over‐ only about 6500 t in 2015 (Figure 25.2). Over‐exploitation,
exploited. Although abalone are geneally exploited for illegal harvesting, disease, increased predation, and
their meat, the nacre layer inside the shell of some spe-
cies, such as the New Zealand paua (H. iris), is also used, 1 http://www.fao.org/fishery/statistics/global‐aquaculture‐
and is the basis for pearl production. Abalone pearl farms production/query/en
have been developed in several countries, including New http://www.fao.org/fishery/statistics/global‐
Zealand, Korea, and the USA. capture‐production/query/en
Aquaculture: Farming Aquatic Animals and Plants, Third Edition. Edited by John S. Lucas, Paul C. Southgate and Craig S. Tucker.
© 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd.
Production (103 t/yr)574 Aquaculture fishery in Australia has also declined over the past
few years but, in this case, the decline was due to the
Figure 25.1 Inside and outside of the shell of the South African outbreak of a serious abalone disease in both farmed
abalone, Haliotis midae. Source: Reproduced with permission from and wild stocks (Mayfield et al., 2011).
Peter Cook.
Another example of a fishery in trouble is that in
120 South Africa where abalone populations (H. midae)
100 Aquaculture have suffered from many years of illegal over‐
exploitation by poachers. As a result of this, the fishery
Fisheries was de‐commercialised in 2008. The fishery was recently
80 re‐opened to a small experimental quota (96 t for the
60 traditional fishing zones in the Western Cape Province;
40 and a 30 t experimental TAC for community based
20 harvest in the Eastern Cape Province), its future remains
uncertain for as long as the illegal exploitation continues.
0 Although some countries, such as South Africa and
1950 1960 1970 1980 1990 2000 2010 Canada, are attempting to rebuild stocks, it seems
Figure 25.2 Total global production of abalone from aquaculture unlikely that fisheries will ever be restored to former
and legal fisheries over the period 1950–2015. Data from FAO. levels (Lessard and Campbell, 2007).
Source: Reproduced with permission from John Lucas.
At the same time as landings from legal fisheries were
habitat degradation have all contributed to this decline. declining, farm production was rapidly expanding in
Following such declines, several fisheries have suffered several countries Figure 25.2. Japan was probably the
severe quota restrictions, or have been completely de‐ first country to culture juvenile abalone on a large scale
commercialised. In California, for example, the commer- but, since then, many other countries have developed
cial exploitation of all species of abalone has been farms, and there are now farms in most countries with a
prohibited since 1997, and whilst a small recreational history of commercial fisheries. In the 1970s, farm pro-
fishery still remains open north of the Golden Gate duction was almost negligible, and although production
Bridge, the commercial fishery has remained closed increased steadily throughout the 1980s and 1990s it is
(California Department of Fish and Wildlife, 2014). The only since about 2000 that the really big increases have
California Department of Fish and Wildlife is developing taken place as countries such as China and South Korea
a red abalone (H. rufescens) Fishery Management Plan, started farming abalone.
the purpose of which is to further refine and implement
long term management objectives, with the hope that Table 25.1 shows changes in abalone production in
the fishery may, one day, be re‐opened. The abalone various countries between 2010 and 2015. Whilst farm
production in most countries, over this period, has either
been stable or has grown very slowly, production in
China and Korea has increased very rapidly. In contrast,
however, in both Chile and Taiwan the volume of
production has decreased over this period, in both
cases following disease problems.
The most significant change has been in China where
the vast majority of the world’s abalone are now pro-
duced. In 2010 there were over 300 abalone farms in
China, with the largest producing over 1000 t/yr.
Although falling prices and Chinese austerity measures
have resulted in the closure of some farms, the total
p roduction for 2015 is now estimated at 115 397 t/yr.
Over the past few years, many Chinese abalone farms
have become more efficient by changing from land‐
based to sea cage operations, and innovations in low‐
cost seed production have helped to establish a viable
industry. Abalone in sea cages are generally fed a mixture
of seaweeds, much of which is grown on farms at nearby
locations. Although disadvantages of sea‐based farms
include bio‐fouling of nets that requires regular cleaning
Table 25.1 Estimated farm production (t) in various regions Abalone 575
in 2010 and 2015.*
close together, with individual bays sometimes housing
Region 2010 production 2015 production hundreds of net cages. This leads to a situation where the
potential for the spread of disease is huge and it seems
China 42 373 115 397 likely that, should a serious disease outbreak occur, this
Korea 5000 9400 could spread very quickly.
Chile 1500 700
South Africa 1023 1400 Over the past decade or so, Korea has become an
Japan (seeds only) 200 200 important supplier of abalone to the world market.
Australia 500 900 Before 2000, only small quantities of abalone were
Taiwan 300 171 farmed, and the production method mainly used
USA (including Hawaii) 200 362 suspended baskets in land‐based farms. Like China,
New Zealand 90 100 production in Korea has evolved to a more efficient
Mexico 33 30 methodology, utilizing off‐shore cage farms. This change
Europe 10 15 has resulted in rapid increases in volume of production,
Thailand 10 8 going from about 1000 t in 2003 to 9400 t in 2014.
Philippines 4 4
In Korea, abalone seeds are produced in about 500
* Data presented at the International Abalone Conference, hatcheries and juveniles are reared using approximately
Korea, 2015. 500 000 sea cages (Park and Kim, 2013). The majority of
Source: Reproduced with permission from Peter Cook. Korean production is in remote Wando County in South
Jeolla Province. Whilst the majority of abalone is con-
of cages, and that farms are subject to the vagaries of sea sumed in domestic markets, the volume being exported
conditions, abalone in sea cages can be grown to market to countries such as Japan, China, the United States, and
size at much lower costs than in land‐based farms. Taiwan has increased from about 70 t in 2004 to about
1115 t in 2014. This has had an important influence on
The southern Chinese Provinces of Fujian and the world market because the majority of Korean
Guangdong are the favoured locations of most farms p roduction is H. discus hannai, the species that is most
whilst the majority of abalone seed production occurs popular, and commands the highest price in the Japanese
between Dalian and Shandong Peninsula in the Northern market.
Province of Liaoning. In 2004, Fujian Province accounted
for over 60% of all abalone produced and sold in China, Farm production of abalone in Korea has not been
and a significant proportion of the Fujian total was the without its problems. High mortalities at the seed
lower value species, H. diversicolor supertexta, which gen- p roduction phase, and slow growth rates in grow‐out
erally sold for less than USD 20/kg. In 2015 the situation tanks, have plagued the industry for many years. Recent
was quite different with more than 95% of production developments in selective breeding programs may,
being of the higher value species, either H. discus hannai however, improve future production efficiency (Park
or a hybrid between H. discus hannai and H. discus discus. and Kim, 2013).
This change was probably brought about because H. dis-
cus hannai is the preferred species in Japan, and China is Farmed abalone production in the USA (including
now beginning to export part of its production to Japan. Hawaii) currently totals about 362 t. It is unlikely; how-
ever, that total production along the Californian coast
There are many challenges to abalone farming in will increase much in the future because of very high
China. Mass mortalities have occurred in nursery and land values and high compliance costs. An aerial view of
postlarval seed production facilities in both the northern a Californian abalone farm is shown in Figure 25.3,
and southern regions, and summer mortality remains a illustrating the quantity of coastal land required.
major problem for H. discus hannai in most bays in
southern China. Extreme weather events, such as very In Europe, abalone farming is a very small, but grow-
cold water in the northern regions, and typhoons ing, industry. Farms are located in the UK, the Channel
and red tides in the southern regions, have caused high Islands, Ireland, France, and Spain. In the UK, a small
mortalities of adults in grow‐out systems. In Fujian and number of farms are located on the south coast of
Guangdong, abalone farms are usually crowded very England, but these are mainly at the experimental level
and production is currently insignificant. In Ireland
farms are also mainly experimental, producing mostly
H. discus hannai, but it seems unlikely that production
will exceed about 3 t in the near future, whilst in the
Channel Islands there are two farming companies, cur-
rently producing less than 1 t/yr. French farms are located
in Brittany and Vendee, and these have the advantage of
576 Aquaculture
Figure 25.3 Aerial view of an abalone farm on the coast of California, USA. Source: Reproduced with permission from R. Fields.
being located in regions where small, natural popula- A discussion of the availability of abalone to the world
tions of abalone occur, and have been fished for some market would not be complete without mention of the
years. Farm production from the French farms is likely to illegal trade. Cook and Gordon (2010) suggested that in
increase over the next few years, but the most significant 2008, the worldwide illegal catch totalled about 5 300 t,
increase in European abalone production is likely to this being equivalent to over 60% of the total legal catch
come from the farm that is developing in Spain, which from fisheries. The majority of the illegal catch comes
plans to greatly expand production in the near future. from South Africa, Australia, and New Zealand, with
Total combined production from all European farms is smaller quantities originating from the USA, Mexico,
currently less than 30 t/yr. Abalone farming in Europe and Chile. Sustained efforts to reduce poaching in
currently suffers from fragmentation of the industry into several of these countries have yielded some positive
many small individual operations. A recently introduced results, but there is no doubt that the large quantities of
project called ‘SUDEVAB’ is a serious attempt to improve illegal catch, that still enter the world market, have a
this. Its objectives include the development of a transna- seriously destabilising effect on trade.
tional organisation of European Abalone Producers. If
this initiative succeeds, it may help farms to achieve 25.3 Biology
overall lower production costs.
Good summaries of the biology of abalone have been
Other countries that produce significant quantities of provided by Hahn (1989), Shepherd et al. (1992) and
farmed abalone are Chile, Japan, South Africa, Australia, Leighton (2000).
Taiwan, and New Zealand, with smaller quantities being
produced in Mexico, Thailand, the Philippines, and Oman.
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