will facilitate regulation and monitoring of the shell-fish industry to the consumer’s benefit.

See also: Parasites: Occurrence and Detection;

Salmonella: Salmonellosis; Vibrios: Vibrioparahaemolyticus; Vibrio vulnificus; Viruses

Further Reading

Anderson DM, Cembella AD and Hallegraeff GM (eds)(1998) Physiological Ecology of Harmful Algal Blooms.NATO ASI Series G: Ecological Sciences, vol. 41. Berlin:NATO.

Bricelj MV and Shumway SE (1998) Paralytic shellfishtoxins in bivalve molluscs: occurrence, transfer kineticsand biotransformation. Reviews in Fisheries Science 6:315–383.

Falconer IR (ed.) (1993) Algal Toxins in Seafood andDrinking Water. London: Academic Press.

Gosling E (ed.) (1992) The Mussel Mytilus: Ecology, Physi-ology, Genetics and Culture. Amsterdam: Elsevier.

Hackney CR and Pierson MD (eds) (1994) EnvironmentalIndicators and Shellfish Safety. London: Chapman andHall.

Hallegraff GM, Anderson DM and Cembella AD (eds)(1995) Manual on Harmful Marine Microalgae. IOCManuals and Guides no. 33. Paris: UNESCO.

Langston WJ and Bebianno MJ (eds) (1998) Metal Metab-olism in Aquatic Environments. Ecotoxicology Series,vol. 7. London: Chapman and Hall.

Lasserre P and Marzollo A (eds) (2000) The Venice LagoonEcosystem. Inputs and Interactions Between Land andSea. Man and The Biosphere Series, vol. 25. Paris: Par-thenon Publishing.

Lees D (2000) Viruses and bivalve shellfish. InternationalJournal of Food Microbiology 59: 81–116.

Livingstone DR (1991) Organic xenobiotic metabolism inmarine invertebrates. In: Gilles R (ed.) Advances inComparative and Environmental Physiology, vol. 7,pp. 1–185. Berlin: Springer-Verlag.

Livingstone DR (1992) Persistent pollutants in marine in-vertebrates. In: Walker CH and Livingstone DR (eds)Persistent Pollutants in Marine Ecosystems. SETACSpecial Publication Series, pp. 3–34. Oxford: PergamonPress.

Livingstone DR (1998) The fate of organic xenobiotics inaquatic ecosystems: quantitative and qualitative differ-ences in biotransformation by inverebrates and fish.Comparative Biochemistry and Physiology 120A:43–49.

Reguera B, Blanco J, Fernandez ML and Wyatt T (1998)Harmful Algae. Xunta de Galicia and IntergovernmentalOceanographic Commission of UNESCO. Spain:Grafisant.

Thurnham DI and Roberts TA (eds) (2000) Health and thefood-chain. British Medical Bulletin 56: 236–252.

Walker CH, Hopkin SP, Sibly RM and Peakall DB(1996) Principles of Ecotoxicology. London: Taylorand Francis.

SHELLFISH/Aquaculture of Commercially Important Molluscs and Crustaceans 5245

Aquaculture of CommerciallyImportant Molluscs andCrustaceansP F Duncan, The University of the Sunshine Coast,

Maroochydore DC, Queensland, Australia

Copyright 2003, Elsevier Science Ltd. All Rights Reserved.

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Background

Aquaculture is the managed cultivation of aquaticorganisms for food or profit and now contributesapproximately 36% of total global fishery produc-tion. As capture fisheries have declined or plateauedover the last decade, aquaculture is the alternativesupply for increasing aquatic product demand andhas been growing at a rate of 10% per annum since1990. Aquaculture products are diverse, with mol-luscs, crustaceans, finfish, and algae predominating.This section deals with molluscs and crustaceanswhose global production volumes are considerable,for example, the pacific oyster (Crassostrea gigas) 3.6million tonnes, carpet clams (Ruditapes philippi-narum) 1.8 million tonnes and various penaeid prawnspecies (Penaeus spp.) 0.9 million tonnes. Productionmethods for mollusc and crustacean aquaculture varyfrom subsistence level, artisinal scale to high intensitymanaged systems. This article covers the key species,production quantities, methods and sources, andcurrent and future issues.

General Characteristics of Aquaculture Species

The basic requirement for all aquaculture species in-clude market acceptability, established productionmethods, availability of appropriate and economic-ally viable feeds, and biological characteristics suit-able for culture. These include high growth rates,captive reproduction or seed stock availability, toler-ance to environmental variation (e.g., temperature),disease resistance, and behavioral characteristicsamenable to high-density culture.

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Molluscs

Molluscs, and particularly bivalves, are well suited toaquaculture. The principal groups include oysters(Family Ostreidae), mussels (Family Mytilidae), scal-lops (Family Pectinidae) and clams (various taxo-nomic groups), which constitute 87% of the 10.1million tonnes (Table 1 and see Shellfish: Commer-cially Important Molluscs). All of these bivalves havea high market demand and feature in the traditionaldiets of most human cultures. Recently, increasingaffluence and health benefits associated with seafood

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tbl0001 Table 1 Aquaculture production of principal mollusc groups

and species (see also Shellfish: Commercially Important

Molluscs)

Species Quantity (tonnes)

Oysters 3 711 606

Crassostrea gigas 3 600 459

Scallops 951 866

Patinopecten yessoensis 928 724

Mussels 1 451 032

Mytilus edulis 498 461

Other Molluscs 4 017 574

Ruditapes philippinarum (Manila clam) 1 820 413

Solen spp. (razor clams) 479 252

Anadara granosa (blood cockle) 315 811

Total 10 132 078

From FAO (2001) FAO Yearbook, Fishery Statistics: Aquaculture Production1999. Fisheries Series No. 58, vol. 88/2. Rome: FAO.

5246 SHELLFISH/Aquaculture of Commercially Important Molluscs and Crustaceans

consumption have increased the demand for theseproducts.

Mollusc Nutrition

Almost all cultivated molluscs are bivalves and there-fore herbivorous or omnivorous filter feeders, con-suming planktonic microalgae and organic detritus.Tridacnid (giant) clams are filter feeders with add-itional nutrition from symbiotic photosyntheticalgae contained within their tissues. The main culti-vated Gastropod group, abalone (Family Haliotidae)consists of herbivorous micro- or macroalgae grazers.All are therefore low trophic-level feeders and eitherobtain nutrients from their surrounding environmentor have it supplied during hatchery-based cultureperiods. Although production of microalgae requiresequipment and expertise, it is not technically difficultor expensive relative to the provision of the morecomplex crustacean and finfish diets. Abalone differowing to their grazing habit. After the larval phase,juvenile abalone are provided with plates coveredwith bacterial and algal films. In growout systems,fresh macroalgae (e.g., Laminaria japonica) or re-cently developed artificial diets are supplied.

Production Methods (Bivalves)

Owing to the shared biological characteristics ofbivalves, the basic principals of culture are similar.

Hatchery Egg production (fecundity) is high,typically several to tens of millions of eggs perspawning, e.g.,scallops and oysters, respectively.Spawning of mature adults occurs in the wild orunder controlled hatchery conditions. Spawningmay be induced by temperature change, emersion,exposure to UV-treated water or chemical inducers,e.g., serotonin. A planktonic larval phase follows

hatching, which, in the wild, acts to disperse thejuveniles from the parent stock. The larval phase,which may last from days to weeks, depending onthe species, consists of several developmental stages.A ciliated trochophore larva occurs after hatching,and as shell secretion continues, the swimming larvabecomes a veliger and finally, near metamorphosis toa non-swimming form, a pediveliger, which has anactive foot for crawling. Under hatchery conditions,the larval phase occurs in large-volume tanks, typic-ally between 5 and 40 m3. For balanced nutrition,larvae are fed on mixed microalgal cultures, e.g.,Chaetoceros spp., Pavlova spp., Isochrysis spp., andTetraselmis spp.

Settlement At metamorphosis, larvae settle on toeither natural or artificial substrates, and at thisstage, collection of spat, or settled bivalves, occurs.In the wild, spat are collected on suspended or fixedmaterial substrates, such as ropes (e.g., mussels),shell, stones, wooden structures (e.g., oysters), ormesh-filled suspended bags (e.g., scallops). Similarmaterials can be introduced into larval rearing tanksto collect spat in hatcheries.

Bivalve spat attach via proteinaceous byssalthreads (e.g., mussels, scallops) or by direct cementa-tion of the lower valve (oysters). Byssally attachedspat may be easily removed manually or by mech-anical stripping. Many scallop species stop byssalattachment around 15 mm and may be collecteddirectly from settlement bags. Mussels attachthroughout life. Oysters may be removed manuallyor retained on settlement material for further grow-out. All bivalves are size-graded and thinned beforetransfer to growout systems, producing a more con-sistent-sized product and a culture density to maxi-mize growth and survival.

Growout Growout to commercial size typicallytakes from 12 months to 4 or 5 years (in the case ofsome temperate scallops and abalone). However,most cultured bivalves are an annual or 2-yearcrop, e.g., blue mussels (Mytilus edulis) 12–18months, greenlip mussels (Perna canaliculus) 18months, Manila clam (Tapes philippinarum) and theAustralian rock oyster (Saccostrea glomerata) ap-proximately 24 months.

As filter feeders, bivalves grow optimally in sus-pended culture system, which maximizes access tofood. Consequently, most bivalves are grown in thisway, although some exceptions, such as clams andsome oysters, are grown on, or in, the bottomsubstrate.

Suspended culture systems are generally basedon hanging a form of enclosure from a surface, or

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SHELLFISH/Aquaculture of Commercially Important Molluscs and Crustaceans 5247

subsurface floating structure. Alternatively, oystersmay be held just off the bottom on a series of traysand frames. The most common systems employ alongline, a rope, up to 250 m or longer, supportedby floats and anchored to the seabed at several pointsto ensure stability. From this main rope are hungvertical droppers that hold animals directly, e.g., bys-sally attached mussels, or, for ear-hung scallops, theshell is pierced and attached via nylon line.

More commonly, a cage or net holds animals. Lan-tern nets are a collapsible net stocking with multiplehorizontal platforms holding shells, individual pearlnets have a rigid frame, and vertical panel nets con-tain numerous pockets in which individuals areplaced. For lower-intensity operations, or for someparticular species, such as the South-East Asian Rudi-tapes and Meretrix clam species, and the Americanhard clam (Mercenaria mercenaria), growout is basedon seeding of suitable sandy/mud nearshore areas.The juveniles may be produced in the hatchery orcollected in the wild.

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Production Methods (Gastropods)

The main gastropods under cultivation are abalone,and, although production systems are still underdevelopment, their high value and declining wildharvest give them significant potential. Productionnow comes from China, Chile, South Africa, Austra-lia, New Zealand, and the USA. The principal culturemethods include a suspended lantern net system,using larger and more structurally complex cagesthan for bivalves, and raceway culture in long,narrow glass fiber or concrete tanks, within whichflat plates are inclined to provide shelter and a surfacefor growth of algal feed. Tidal pond culture is alsopracticed in China, though less frequently than othermethods.

Abalone culture relies on hatchery-producedjuveniles, and broodstock are spawned using similarmethods to bivalves. The larval development ofabalone is similar, though shorter at 7 days or less,and nonfeeding, so provision of algae is not necessary.At settlement, the larvae metamorphose into thebottom-living form. This transitional phase fromlarvae to settled juveniles remains the period ofhighest mortality. At settlement, larvae are inducedto attach to corrugated plastic or tiles, which have asurface growth of algal and bacterial cells. The juven-iles feed on these films and, as growth continues,are transferred to nursery and growout systems.The options of open-water ranching or restockingdepleted areas have also been attempted and havethe advantage of no management input, but the dis-advantage of little control over stock.

Current Issues and Future Prospects

As with most aquaculture, there is a tendency awayfrom wild seed collection, for sustainability andsupply reasons, but also for benefits from hatcheryproduction. These include genetic selection (e.g.,faster growth rates, disease resistance) and geneticmanipulation to develop polyploid animals, i.e.,three or four copies of genes, compared with two.Polyploid animals may be reproductively inactive,essential for translocation of non-native species toopen-water systems, and often show increasedsomatic growth rates owing to reduced gonadal de-velopment. Continued vigilance in the control anddetection of toxic algal blooms and monitoringfor product safety will remain significant issues ifpublic confidence in mollusc consumption is to bemaintained.

Crustaceans

Most aquacultured crustaceans belong to the ClassMalocostraca, Order decapoda, e.g. prawns/shrimps,crabs, lobsters, although brine and mysid shrimp(Classes Branchiopoda and Mysidacea) and copepods(Class Copepoda) are also produced in small quan-tities as live feeds for other aquaculture species,such as finfish. Decapod production is dominated bythe marine penaeid prawns, with the black tigerprawn (Penaeus monodon) being the most widelycultivated crustacean worldwide. In 1999, produc-tion was 575 842 tonnes, predominantly from Asia,with an estimated value of US$3.65 billion. P. vanne-mei and P. chinensis are the aquacultured penaeids inthe Americas and China, respectively, contributing359 196 tonnes. Penaeids are grown worldwide(Table 2).

The giant river prawn (Macrobrachium rosenber-gii), is the most widely cultured freshwater decapodcrustacean, with production in 1999 of 102 124tonnes, worth US$416 million. It has been introducedinto many countries, including North and SouthAmerica, Africa, Asia, and the Pacific Islands.China, Bangladesh, and Taiwan account for over90% of production. Freshwater crayfish culture iswidespread and based on six main species (in orderof quantity): Procambarus clarkii, Pacifastacusleniusculus, Astacus leptodactylus, Cherax destruc-tor, and C. quadricarinatus. Total productionamounted to 21 171 tonnes in 1999, with US produc-tion of P. clarkii over 19 000 tonnes alone. Otherminor species are produced locally (Table 3).

Crab aquaculture production is relatively smalland dominated by the freshwater Chinese river crab(Eriocheir sinensis) at 171 955 tonnes in 1999.

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tbl0002 Table 2 Principal aquacultured penaeids and main production

sources

Species Sources

Penaeus monodonGiant tiger prawn

Thailand, India, Vietnam,

Indonesia, Philippines

Penaeus vannameiWhiteleg shrimp

Ecuador, Mexico, Brazil, Colombia

Penaeus merguiensisBanana prawn

Vietnam, Indonesia

Penaeus stylirostrisBlue shrimp

Ecuador

Penaeus chinensisFleshy prawn

China, Korea

Penaeus japonicusKuruma prawn

Japan, China, Australia

Penaeus indicusIndian white prawn

India, South Africa

tbl0003 Table 3 Principal aquacultured freshwater crayfish and main

production sources

Species Source

Procambarus clarkiiRed swamp crawfish

USA, Mexico, France (I)

Pacifastacus leniusculusSignal crayfish

France (I), Spain (I)

Astacus leptodactylusDanube crayfish

France

Astacus astacusNoble crayfish

France

Cherax destructorYabby

Australia

Cherax quadricarinatusRedclaw crayfish

Australia, Argentina (I), Mexico (I)

Cherax tenuimanusMarron

Australia, South Africa (I)

I, introduced.

5248 SHELLFISH/Aquaculture of Commercially Important Molluscs and Crustaceans

Additional species under small-scale culture, but withpotential, include the mud crab (Scylla serrata) andvarious portunid swimming crabs.

Lobster culture worldwide is extremely small, 58tonnes from four different Panulirus spp., a tropical/subtropical genus. The slow development of lobsterculture is due to a relatively long larval cycle that istechnically difficult to replicate in hatcheries.

Crustacean Nutrition

The larval stages of crustaceans vary in their nutri-tional requirements. Typically, under hatchery condi-tions, early stages feed on stored yolk, before movingto phytoplankton then zooplankton, e.g., Artemia(brine shrimp) larvae or rotifers. Crabs and lobstersmay be carnivorous from hatching.

Penaeid prawns are fed a processed pelleted diet,consisting principally of marine fish meal, and

additionally balanced for nutritional requirements.The food conversion ratio, i.e., the quantity of feed(kg) required to produce 1 kg of product is typicallyaround 1.5–2.5:1, in semi-intensive/intensive penaeidproduction systems.

Feed is a major cost and may constitute around30% of production costs. Uneaten feed is a majorcontributor to poor water quality, and nutrient-richwaste water contributes to external environmentalimpacts. Feed management is vital for successfulaquaculture.

Freshwater crayfish are omnivores and obtainmuch of their nutritional requirements from theculture environment in the form of organic detritus.Grain-based pellets, or hay, are often added to pondsto provide additional feed and promote pond prod-uctivity by enhancing nutrient levels.

Crabs, such as Scylla spp., are also omnivores butwith a tendency towards animal protein. Crab aqua-culture is still relatively undeveloped, to the extentthat no standard feed is produced or used. Mostproduction is from South-east Asia, and much use ismade of local feed sources such as trash fish andshrimp, squid, and plant meals such as soy. Penculture in mangrove areas also provides additionalnutrition in the form of fallen mangrove leaves.

A feeding behavioral characteristic of many crust-aceans, and one that heavily influences productionmanagement, is cannibalism. Crustaceans are mostvulnerable immediately after molting, a regular pro-cess essential for growth. When the old, hard exo-skeleton is shed, the animal is soft until the new shellhardens and is vulnerable to predation, especially ifstocking densities are high. Cannibalism is lesscommon in penaeids and crayfish, where it is man-aged by appropriate stocking, size grading and feed-ing regimes, but more common in crabs and lobsters.Similar management strategies are again employedbut are not wholly effective. As a consequence, crabproduction densities tend to be low, and separationinto individual culture vessels has been employed forcultivated soft-shell crab and Hommarid lobsters.The associated cost of this makes it viable onlyfor high-value products, or short-term culture ofjuveniles for restocking purposes.

Production Methods

Decapod crustaceans are characterized by complexand diverse larval cycles, which, as previously noted,have contributed to their relative ease and develop-ment of aquaculture. Differences in larval cycles alsocontribute todifferences inproductionmethodologies.

Hatchery The most commonly cultured crustaceans,the penaeid prawns, are unusual in having no maternal

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SHELLFISH/Aquaculture of Commercially Important Molluscs and Crustaceans 5249

care, and fertilized eggs are shed directly into thewater. Most decapods retain the developing larvae,within the egg, on modified appendages beneath theabdomen, e.g., freshwater crayfish and crabs, andrelease larvae at a later developmental stage.

For aquaculture operations, mature broodstock aretypically sourced from wild populations, althoughfarm-reared broodstock are becoming more commonas they enable reliable supply and the opportunity forgenetic selection. Broodstock are maintained in spe-cialized spawning tanks, under conditions of reduceddensity and high-quality nutrition favoring gonaddevelopment. Environmental variables such as tem-perature and light intensity are also controlled toreduce stress and promote gonad maturation. Matinginvolves transfer of a sperm package that the femaleretains until required, and fertilization typicallyoccurs as the eggs are released. Spawning occursunder relatively predictable circumstances followingovary maturation, enabling hatcheries to harvest eggsas they are produced.

Penaeid eggs hatch within about 12 h into thenauplius phase, which persists through several stages,before progressing through major metamorphosesinto protozoeal, mysis, and postlarval phases. Theduration of the whole larval cycle, up to saleablepostlarva (PL) is typically around 20–25 days. Thelarval phase, whether in open water or in the hatch-ery, is a free swimming period, becoming the morefamiliar bottom-living form after the postlarvaephase.

Growout Typically, the postlarval stage is trans-ferred from the hatchery to grow out ponds, althoughsome operations also have intermediate nurserygrowout or conduct growout in indoor, tank-basedsystems under high-density conditions. However,growout is generally earthen pond-based, ranging insize from less than 0.5 ha to over 10 ha, althoughlarger ponds are typically harder to manage effect-ively. Ponds are generally 1–2 m in depth and arestocked with PL at between 1 (or less) to more than100 PL m�2, depending on the production type. Forexample, Australian stocking rates for P. monodonunder relatively intensive 1-ha pond production is30–40 PL m�2.

During the production cycle of 3–4 months, waterquality is managed through aeration, water exchange,and a phytoplankton bloom, which tends to stabilizephysicochemical water parameters, e.g., oxygen,carbon dioxide, pH. Feed is provided three or fourtimes per day, with consumption closely monitoredand adjusted as necessary. Production from such inten-sive penaeid culture is typically 5–10 tonnes per hec-tare per crop but varies with species and management.

For other crustaceans, the principal differences inlarval development and production methods areas follows.

Freshwater Crayfish Females hold 500–800 eggsunder the abdomen that hatch as miniature crayfishafter 2–10 weeks, depending on the temperature andspecies. Juveniles are collected and graded for sizeand gender, and stocked at around 5–15 m�2

(e.g.C. quadricarinatus), typically into earthenponds. Production of this species seldom exceeds 1–1.5 tonnes per hectare per crop, owing to lower dens-ities and lower intensity management.

Crabs The crab larval phase begins as a zoea, ofwhich there are five, followed by megalopa thencrab. Although still developmental, pond-based cul-ture for Scylla spp. crabs appears feasible. Small-scalecommercial trials have indicated that monosex cul-tures, low–medium stocking densities, and provisionof shelters, to protect newly moulted individuals fromcannibalism, provide improvements on current low-intensity culture systems. Polyculture with penaeids,as a secondary crop, also occurs.

Perhaps the greatest opportunity for value addingto crab culture is a soft-shell product. Soft-shell crabshave been a valuable secondary product of the easternUS blue crab (Callinectes sapidus) fishery for morethan 100 years. The development of culture tech-niques, and the ability to control aspects of molting,should enable commercial scale production within afew years. Presently, it remains labor-intensive andconfined largely to South-east Asia.

Macrobrachium spp. have even fewer distinctlarval stages, with several zoea, followed by a pl,then adult. Unusually, the larvae require brackishwater for development, although culture is in freshwater. This finding was critical in enabling thedevelopment of Macrobrachium aquaculture.

Harvest, Handling, and Marketing Harvesting isdependent, to some extent, on the market require-ments. Fresh, frozen, or processed crustaceans aredrain-harvested, with the complete crop being re-moved immediately. This applies to most penaeids,e.g., P. monodon, crabs (except soft-shell, which areharvested at molt), and Macrobrachium spp. Mostlive products, e.g., freshwater crayfish and somepenaeids (P. japonicus), are harvested in smallbatches, typically using baited traps. Harvesting ofcrayfish may make use of their rheotactic behavior,in which the animals self-harvest, by following awater flow up a ramp into a collection chamber.

Crustaceans generally, and prawns in particular,are typically processed and sold as either frozen

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5250 SHELLFISH/Aquaculture of Commercially Important Molluscs and Crustaceans

(cooked, green, whole or tails and as block or indi-vidually quick frozen), fresh chilled, or as a preparedor preserved product, e.g., canned. Aquaculture tendsto concentrate on the higher value fresh or frozenproduct, to offset production costs. Some species,notably, Penaeus japonicus, freshwater crayfish, andsome crabs, e.g., Scylla spp., are marketed livefor value-adding or spoilage reasons. Live kurumaprawn can attract prices of US$75 kg�1 during Japan-ese holiday periods, justifying the significant extraharvest, processing and packaging procedures neces-sary to ensure survival. By contrast, freshwater cray-fish tend to be marketed live to ensure product qualityat market.

Current Issues and Future Prospects

The principal issues affecting penaeid prawn cul-ture worldwide are disease and environmentalimpacts. The possibility of rapid disease spread inhigh-intensity production systems is high, and mor-tality can be significant. At the individual farm level,and outwith epidemic-type outbreaks, producersmanage disease risk through quarantine, exclusionof disease vectors, health testing of stock, and man-agement of water quality and animal density.

On a larger scale, where entire regions are affected,disease impacts, particularly viruses, have been cata-strophic. These outbreaks are harder to manage andappear to be due to overall pathogen levels in stock,both broodstock and pl, and the general status of theculture or external aquatic environment. For example,the passage of whitespot syndrome virus (WSSV) andyellowhead disease through Asia can be traced fromthe early and mid-1990s. Whitespot alone was con-sidered to have resulted in losses of US$600 million inThailand and in excess of US$2 billion throughoutAsia in 1997.

Similarly, taura syndrome virus and WSSV affectedcentral and South American production from around1992.

These diseases occur naturally in the environment,but significant outbreaks occur when animals areproduced under high-density, sub-optimal conditions.However, introductions of diseases, for example fromAsia to the Americas, have occurred.

Disease is also a major concern for freshwatercrayfish production given the impact that the fungusAphanomyces astaci, or crayfish plague, had on wildand captive populations in Europe. As a result,several resistant species have been introduced fromNorth America, now forming the basis of Europeanproduction. The high susceptibility of native Austra-lian crayfish to the fungus has ensured that strictquarantine procedures apply to importations ofpotential vectors.

The environmental impacts of aquaculture, andparticularly prawn farming, have attracted significantdebate in recent years. Largely as a result of unregu-lated development in Asia and South America, prawnaquaculture has been linked with coastal ecosystemdestruction, disease outbreaks and introductions, andunsustainable practices. Consequently, significantenvironmental and planning regulations are nowenforced in many countries new to aquaculture,such as Australia and the USA, and increasingly soin established aquaculture countries. Regulatorymeasures have included limiting farm sizes andnumber, control of discharge water quantity andquality, and the introduction of disease-managementand health-monitoring strategies.

The reliance on fish meal and oil for the productionof animal feeds is an issue facing aquaculture. Esti-mates suggest that fish meal use by aquaculture willincrease from the 35% of total production (6.5 mtonnes in 2000) to 55% by 2010. In addition, fish-oil use by aquaculture was 55% of total production in2000 and is expected to rise to 75% over the sameperiod. Although mostly used in finfish diets, crust-acean feeds also contain significant quantities, andusage should be reduced because of supply-reliabilityissues and energy-conversion inefficiency. Substitu-tion with plant proteins, such as soy, may representviable alternatives.

Crustacean aquaculture offers significant advan-tages over traditional wild-capture fisheries, whichare generally in decline or static. The ability tomanage most aspects of aquaculture means that,theoretically, the environmental impact can be min-imized, which will be essential for public acceptanceof aquaculture product and practices. Waste-nutrientmanagement programs, including the use of plantsand animals to lower nutrient concentrations (bio-remediation), multiple water use for irrigation, andpolyculture will reduce off-farm impacts and improveproduction efficiency. Improved feed management,reduced fish meal usage, and the application of bio-technology, in the form of genetic selection and man-agement, should contribute further to cost reductionand efficiency improvement, enabling aquaculture tocontinue its growth.

Nutritional Features of Commercially ImportantShellfish

Shellfish are high in protein and unsaturated oils, andlow in cholesterol. They are particularly high in o-3and o-6 polyunsaturated fatty acids, which are con-sidered beneficial in reducing high blood pressure,coronary heart disease, arthritis, and some cancers.Consequently, nutritionists and medical authoritieshave promoted their consumption recently. Table 4

tbl0004 Table 4 Proximate nutritional composition (per 100-g fresh weight) of principal aquacultured crustaceans (sources Nettleton (1985),

Yearsley et al. (1999))

Species Protein (g) Total fat (g) Carbohydrate (g) Energy (kJ) Cholesterol (mg) Fattyacids(Saturated/monounsaturated/polyunsaturated/o-3)

Black tiger prawn

Penaeus monodon19.2 0.6 (0.4–0.7) 1.8 394 120–160

a0.28/0.18/0.34/0.07–0.34

b

Freshwater

crayfish

Astacus spp.

16.0 0.05 1.0 76 0.21/0.26/0.33/-c

Blue crab

Calinectes sapidus16.2 1.0 (0.4–2.2) 0.6 81 76 0.17/0.22/0.40/0.38

d

Rock lobster

Panulirus argus19.2 1.2 1.7 100 106

e0.14/0.14/0.59/0.27

aGeneral data for penaeids.

bo-3 range from other penaeids.cData for Cherax quadricarinatus.

dData for Cancer Magister.

eCooked product.

SHELLFISH/Aquaculture of Commercially Important Molluscs and Crustaceans 5251

shows the proximate composition of the importantnutritional components of key cultivated crustaceans.(See also Table 5 in Shellfish: Commercially Import-ant Molluscs.)

See also: Shellfish: Commercially Important Molluscs

Further Reading

Bayne BL (ed.) (1991) The biology and cultivation ofmussels. Aquaculture 94(2–3): 121–278.

Fallu R (1991) Abalone Farming. Oxford: Blackwell.FAO (2001) FAO Yearbook, Fishery Statistics: Aquaculture

Production 1999. Fisheries Series No. 58, vol. 88/2.Rome: FAO.

Fast AW and Lester LJ (eds) (1992) Marine Shrimp Culture:Principles and Practices. Developments in Aquacultureand Fisheries Science, vol. 23. Amsterdam: Elsevier.

Keenan CP and Blackshaw A (1999) Mud crab aquacultureand biology. In: Australian Centre for InternationalAgricultural Research, Proceedings No. 78. Canberra.

Dietary Importance See Fish: Dietary Importan

Landau M (1992) Introduction to Aquaculture. New York:John Wiley.

Matthiessen G (2000) Oyster Culture. Oxford: Blackwell.Nettleton J (1985) Seafood Nutrition: Facts, Issues and

Marketing of Nutrition in Fish and Shellfish. NewYork: Osprey Seafood Handbooks.

New M and Valenti W (eds) (2000) Freshwater PrawnCulture. Oxford: Blackwell.

Philips BF and Kittaka J (2000) Spiny Lobsters, Fisheriesand Culture. Oxford: Blackwell.

Primavera JH (1996) Environment friendly aquaculture andrehabilitation in mangrove ecosystems. In: World Aqua-culture 96. Annual Meeting of the World AquacultureSociety Jan. 29–Feb. 2, Bangkok, Thailand.

Shumway SE (ed.) (1991) Scallops: Biology, Ecology andAquaculture. Developments in Aquaculture and Fisher-ies Science, vol. 21. Amsterdam: Elsevier.

Yearsley GK, Last PR and Ward RD (1999) AustralianSeafood Handbook. Canberra: CSIRO Marine Re-search.

ce of Fish and Shellfish