Biofloc based farming of Nile tilapia (Oreochromis niloticus) in tanks under different stocking densities

This experiment was conducted to optimize the stocking density of Nile tilapia (Oreochromis niloticus) in biofloc based farming system in tanks for a period of 90 days from 23 December to 22 March 2022 in Mohanpur upazilla, Rajshahi district, Bangladesh. The experiment was conducted in 5000 L cemented tanks (5m3) under three different of stocking densities (T1: 200 fishes/m3, T2: 150 fishes/m3 and T3: 100 fishes/m3) having three replicates each. The initial weight of fish was 11.50±0.35 g and fishes were fed (34% protein content) twice a day @ 5-3 % body weight.  Among three treatments, a significantly higher (P<0.05) average daily gain (ADG) of 1.15±0.07 g with specific growth rate (SGR) of 2.44±0.09 % day-1 were recorded in T3 treatment but a significantly higher (P<0.05) average yield of 118907.70 and 114914.20 kg/ha/3 months were obtained in T1 and T2 treatment, respectively. Higher average net benefit of 1231671.90 BDT/ha/3 months and BCR of 0.12 were obtained in T2 treatment which is significantly higher (p<0.05) than T1 and T3 treatment. By an economical assessment, if the sales price is influenced by the final body weight, the reduced average harvest weight in higher stocking densities could lead to low profitability. Therefore, it is concluded that the use of intermediate stocking density, around 150 fishes/m3, has higher profitability since it produces a large proportion of harvested fish that reach high body weights, and possible high selling prices, combined with desirable biomass.