A workshop for farmers on biofloc-based shrimp culture, which has got several advantages and weeding out practical difficulties being faced by the agriculturists was held at the Fisheries College, Tuticorin on Friday.

The biofloc-based shrimp culture is commercialised in the United States and most of the South East Asian countries like China, Thailand, South Korea, Taiwan, Indonesia etc. Among the seafood, shrimp is considered one of the major export commodity and it makes the farmers' economic growth very vibrant and fast because of the short culture period of shrimp while comparing with other cultivable marine organisms.

Generally, in shrimp / fish farming system, ammonia, a nitrogenous waste, is produced from its excretory material and the uneaten feed. In normal farming system, ammonia is converted to nitrite by nitrosomonas bacteria and nitrite (toxic to animal) is converted to nitrate (non toxic to animal) by nitrobacter bacteria. The doubling time of these two groups of bacteria are very slow (more than 72 hours to 1 week). Because of this reason, the farmers change the water to avoid sudden increase of ammonia in the farm.

In the biofloc-based method, heterotrophic bacteria play a major role, as the bacterium needs organic carbon, nitrogen and oxygen for their proliferation. Nitrogen source is already present in the excretory materials of shrimp and uneaten feed. Organic carbon such as molasses, rice bran and cassava powder with addition of oxygen would form the microbial floc.

In this process, the heterotrophic bacteria assimilate ammonia and convert it into bacterial floc and hence, ammonia production in culture system is reduced. It is called biofloc technique, which has several advantages such as minimum land area requirements, bio-security, easy management, reduction of the feed cost, (25 per cent protein is enough of L. vannamei), maintaining good water quality, control of pathogenic bacteria, nil or limited water exchange and protection of the natural environment. Hence, the workshop provided information related to biofloc-based shrimp farming to agriculturists. R. Prabakaran, Vice-Chancellor, Tamil Nadu Veterinary and Animal Sciences University inaugurated the workshop in the presence of Yoram Avnimelech, Director, World Aquaculture Society and Technion, Israel Institute of Technology and V. K. Venkataramani, Director (Fisheries).

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