- Freshwater prawn farm
:"This article is about the farming of freshwater prawns. For the farming of marine (saltwater) shrimps, see
shrimp farm ing."A freshwater prawn farm is an
aquaculture business designed to raise and produce freshwaterprawn orshrimp fn|1 for human consumption. Freshwater prawn farming shares many characteristics with, and many of the same problems as, marineshrimp farm ing. Unique problems are introduced by the developmental life cycle of the main species (thegiant river prawn , "Macrobrachium rosenbergii").New, M. B.: " [http://library.enaca.org/Shrimp/Publications/FAO_Macrobrachium_manual_2003.pdf Farming Freshwater Prawns] "; FAO Fisheries Technical Paper 428, 2002. ISSN 0429-9345.]The global annual production of freshwater prawns (excluding
crayfish andcrab s) in 2003 was about 280,000 tons, of which China produced some 180,000 tons, followed by India and Thailand with some 35,000 tons each. Additionally, China produced about 370,000 tons ofChinese river crab ("Eriocheir sinensis").Data extracted from the [http://www.fao.org/figis/servlet/static?dom=collection&xml=global-aquaculture-production.xml FAO Fisheries Global Aquaculture Production Database] for freshwater crustaceans. The most recent data sets are for 2003 and sometimes contain estimates. Accessed June 28, 2005.]Species
All farmed freshwater prawns today belong to the
genus "Macrobrachium ". Until 2000, the only species farmed was theGiant river prawn ("Macrobrachium rosenbergii", also known as theMalaysian prawn ). Since then,China has begun farming theOriental river prawn ("M. nipponense") in large quantities, andIndia farms a small amount ofmonsoon river prawn ("M. malcolmsonii"). In 2003, these three species accounted for all farmed freshwater prawns, about two thirds "M. rosenbergii" and one third "M. nipponense".There are about 200 species in the genus "Macrobrachium". They occur throughout the tropics and subtropics on all continents except Europe.
Biology of "Macrobrachium rosenbergii"
Giant river prawns live in turbid
freshwater , but their larval stages requirebrackish water to survive.Males can reach a body size of 32 cm;females grow to 25 cm. In mating, the male depositsspermatophore s on the underside of the female's thorax, between the walking legs. The female then extrudes eggs, which pass through the spermatophores. The female carries the fertilized eggs with her until they hatch; the time may vary, but is generally less than three weeks. A large female may lay up to 100,000 eggs.From these eggs hatch
zoea e, the first larval stage ofcrustacean s. They go through several larval stages before metamorphosing into postlarvae, at which stage they are about 8 mm long and have all the characteristics of adults. This metamorphosis usually takes place about 32 to 35 days after hatching. These postlarvae then migrate back into freshwater.There are three different
morphotype s of males. The first stage is called "small male" (SM); this smallest stage has short, nearly translucent claws. If conditions allow, small males grow and metamorphose into "orange claws" (OC), which have large orange claws on their secondcheliped s, which may have a length of 0.8 to 1.4 their body size. OC males later may transform into the third and final stage, the "blue claw" (BC) males. These have blue claws, and their second chelipeds may become twice as long as their body.Wynne, F.: " [http://aquanic.org/publicat/state/ky/prawn_ext.htm Grow-out Culture of Freshwater Prawns in Kentucky] ", 2000. Last accessed July 4, 2005.]Male "M. rosenbergii" have a strict hierarchy: the territorial BC males dominate the OCs, which in turn dominate the SMs. The presence of BC males inhibts the growth of SMs and delays the metamorphosis of OCs into BCs; an OC will keep growing until it is larger than the largest BC male in its neighbourhood before transforming. All three male stages are sexually active though, and females who have undergone their pre-mating molt will cooperate with any male to reproduce. BC males protect the female until their shell has hardened, OCs and SMs show no such behavior.
Technology
Giant River Prawns have been farmed using traditional methods in south-east Asia for a long time. First experiments with artificial breeding cultures of "M. rosenbergii" were done in the early 1960s in
Malaysia , where it was discovered that the larvae needed brackish water for survival. Industrial-scale rearing processes were perfected in the early 1970s inHawaii , and spread then first toTaiwan andThailand and then to other countries.The technologies used in freshwater prawn farming are basically the same as in marine
shrimp farm ing. hatcheries produce postlarvae, which then are grown and acclimated in nurseries before being transferred into growout ponds, where the prawns are then fed and grown until they reach marketable size. Harvesting is done by either draining the pond and collecting the animals ("batch" harvesting) or by fishing the prawns out of the pond using nets (continuous operation).Due to the aggressive nature of "M. rosenbergii" and the hierarchy between males, stocking densities are much lower than in
penaeid shrimp farms. Intensive farming is not possible due to the increased level of cannibalism, so all farms are either stocked semi-intensively (4 to 20 postlarvae per square metre) or, in extensive farms, at even lower densities (1 to 4/m²). The management of the growout ponds must take into account the growth characteristics of "M. rosenbergii": the presence of blue-claw males inhibits the growth of small males, and delays the metamorphosis of OC males into blue-claws. Some farms fish off the largest prawns from the pond using seines to ensure a healthy composition of the pond's population, designed to optimize the yield, even if they employ batch harvesting. The heterogeneous individual growth of "M. rosenbergii" makes growth control necessary even if a pond is stocked newly, starting from scratch: some animals will grow faster than others and become dominant BCs, shunting the growth of other individuals.The
FAO considers the ecological impact of freshwater prawn farming to be less severe than inshrimp farm ing. The prawns are cultured at much lower densities, meaning less concentrated waste products and a lesser danger of the ponds becoming breeding places for diseases. The growout ponds do not salinate agricultural land, as do those of inland marine shrimp farms. Freshwater prawn farms do not endangermangrove s, and are better amenable to small-scale businesses run by a family.FAO : [http://www.fao.org/figis/servlet/static?dom=culturespecies&xml=Macrobrachium_rosembergii.xml Cultured Species Fact Sheet "M. rosenbergii"] ; accessed June 30, 2005. Has images.] However, like marinefarmed shrimp , "M. rosenbergii" is also susceptible to a variety of viral or bacterial diseases,Tonguthai, K.: [http://www.fisheries.go.th/aahri/Health_new/AAHRI/AAHRI/Topics/Newsletter/art6.htm "Diseases of the Freshwater Prawn," Macrobrachium rosenbergii] , AAHRI Newsletter 4(2), Aquatic Animal Health Research Institute, Bangkok University; December 1997.] including theWhite Tail Disease Sahul Hameed, A. S.: [http://library.enaca.org/Health/DiseaseLibrary/DiseaseCard-WTD.pdf "White tail disease of "Macrobrachium rosenbergii] , NACA, 2003.] , also called "White Muscle Disease".Sahul Hameed, A. S.: " [http://library.enaca.org/Health/DiseaseLibrary/White_tail_disease.pdf White Tail Disease - Disease Card] ", NACA, 2005.]Economics
The global annual production of freshwater prawns in 2003 was about 280,000 tonnes, of which China produced some 180,000 tonnes, followed by India and Thailand with some 35,000 tonnes each. Other major producer countries are
Taiwan ,Bangladesh , andVietnam . In theUnited States , there are only a few hundred small farms for "M. rosenbergii" with an overall production of just about 50 tonnes in 2003. The U.S. is, though, the largest producer of farmedcrayfish . In 2003, U.S. farms produced 33,500 tonnes of red swamp crawfish ("Procambarus clarkii"), a crayfish species native toNorth America .See also
*The technologies used in freshwater prawn farming, but also the ecological problems associated with this industry, are basically the same as for marine
shrimp farm ing and are discussed in that article.Footnotes
fnb|1 The terminology is sometimes confusing as the distinction between "
shrimp " and "prawn " is sometimes blurred. Recent aquaculture literature increasingly uses the term "prawn" only for the freshwater forms ofpalaemonid s and "shrimp" for the marinepenaeid s.Indian Aquaculture Authority: " [http://aquaculture.tn.nic.in/pdf/farming.pdf Shrimp Aquaculture and the Environment - An Environment Impact Assessment Report] ", ch. 2; IAA report, April 2001.]References
The main reference for this article was a comprehensive farming manual of the
FAO .
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