Biofloc technology is based on the assimilation of inorganic nitrogen species (ammonia, nitrite and nitrate) by the microbial community present within the water body. The objectives of the present study were to determine the effect of biofloc process on the growth and production of rohu (Labeo rohita) reared at different stocking densities in tank culture and to evaluate economics of the different treatments. The experimental design included three biofloc treatments (with three replications) and three controls (with three replications): biofloc tank fed with 20 per cent crude protein feed and extra carbohydrate and control tank fed with 30 per cent crude protein feed at three different stocking densities, viz., 1.3, 2.6 and 3.9 number fingerlings per m2 of surface area of tank. The fish were cultured for a period of three month. It can also be observed that at higher stocking density average weight of fish decreased. This is because at higher stocking density, fish experiences more stress due to overcrowding and competition for feed. In case of biofloc treatment at low stocking density, average fish growth was higher as compared to other treatments. Specific growth rate (SGR) and protein efficiency ratio (PER) were highest and feed conversion rate (FCR) was lowest for biofloc treatment with lowest stocking density of 1.3 nos/m2. The economics of the different treatments were assessed by their internal rate of returns (IRR). Equivalent Uniform Annual Worth (EUAW) was evaluated for the different treatments as the treatment units had components of different life spans. The internal rate of returns was determined for each treatment by finding the appropriate discounting rates at which EUAW becomes zero. It was found that both EUAW and IRR become maximum in the biofloc treatment at stocking density of 1.3 Nos./ m2.

Keyword: Rohu (Labeo rohita); Aquaculture; Biofloc technology; Economic analysis.