Aquaculture - reproducing the results

Reproducing the results
Aquaculture has been practised for thousands of years and yet a problem that still persists inmodern day fish farming is the reluctance of many species to breed in captivity. Withtraditional fish spawning methods, fish have to be killed in the process. Alternatively, wild fryhave to be caught and transported. The difficulties of getting fish to spawn is one of the reasonswhy there is not yet a wide diversity of fish breeds farmed worldwide, because, for aquacultureproduction to reach its economic potential, the entire life cycle of a species should becompleted in captivity. Reproductive success is also essential forwild species that are endangered and potential fish breeds thatwill be developed by farmers in the future. However, progress isbeing made to overcome these obstacles.
Fish farmers tend to raise their stock at high densities in theartificial precincts of fish ponds and paddies, which means thefish do not receive the environmental stimuli to trigger naturalreproduction. So, working in collaboration, Canadian andChinese researchers have developed a fish breeding technique, the Linpe method, which inducesovulation in female fish by injecting them with a drug-hormone combination. The hormone, asynthetic gonadotropin-releasing hormone analogue (LHRN-A), stimulates the sex organs of thefish whilst the drug domperidone inhibits the action of dopamine, a substance produced by thefish that inhibits ovulation. In China, the spawning kit consists of a vial of the synthetichormone, a vial of the drug, saline solution, and a syringe. Workshops have been held in fishhatcheries and with Chinese farmers to promote acceptance and proper use of the new method.
For commercial use, a Canadian company, Syndel International Inc., has developed a singleproduct, which is now used extensively in India, Pakistan, Taiwan, Malaysia, Indonesia, Nigeriaand Vietnam and, to a lesser extent, in a variety of other developing countries.
Traditional techniques to induce spawning require handling each fish twice and with carp, forexample, fish are raised specifically for obtaining a pituitary extract used to induce spawning.
However, although effective, many fish are sacrificed in the process (up to 80,000 fish/yr) andthe extract has a poor shelf life. This costly technique also entails that females are injected attwo separate intervals to induce ovulation. With the Limpe method however, handling, damageto the fish and the spread of disease are all reduced. It also allows fish farmers to improve themanagement of their hatcheries as they can better predict when spawning will occur.
In Vietnam, CIRAD is working with IRD on the reproduction of two species of Mekong catfish,Pangasius bocouti, known locally as 'ca ba sa', and P.hypophthalmus ('ca tra'). Though culturedin captivity for some time, the process of reproduction has proved problematic, which hasnecessitated the capture of fingerlings in Cambodia and their transport to Vietnam for growingon. However, working in partnership with the Vietnamese company Agifish and the Universityof Can Tho, the process of reproduction was mastered in 1995 and breeding is now beginningto expand.
Agifish, for example has progressed from a production of 30,000 juveniles in floating cages tothe production of 1.6 million fingerlings of P.bocourti and several tens of millions of fingerlings of P.hypophthalmus in 1999. With this breeding success farmers in the An Giang Province of the Mekong Deltaare using a seasonal excess of paddy to farm P. bocourti, whichis allowing them to take advantage of markets in Eastern Europe,America, Japan and Australia.
The world's largest freshwater fish, growing up to 4m long andweighing up to 400kg, is found in Brazil. The pirarucu (Arapaimagigas) is a very fast growing fish and well adapted to fish farming. To date, pirarucu has been bred extensively without controls on reproduction, resultingin annual production of 10-15 tonnes and growth of 10kg a year. However, according to CIRADteam leader in Brazil, Dr Lionel Dabbadie, with controlled reproduction, increasedcommercialization would be possible. Surprisingly perhaps, despite one tenth of the world's fishspecies (~5,000) occurring in the Amazon none of them are farmed on a large scale and on theAmazon flood plain no aquaculture is practised at all, as it is still cheaper to harvest wild stocksof fish. However, the pirarucu is on the list of endangered species and upland rangers are beingencouraged to raise pirarucu and other fish species in ponds.
IDRC - International Development Research Centre, Ottawa, CanadaCIRAD - Centre de coopération Internationale en Recherche Agronomique pour le Développement.
IRD - Institut de Recherche pour le Développement


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