A 120-day cage grow-out production performance of Nile Tilapia, Oreochromis niloticus was conducted in the Dakatia river, Echoli, Chandpur to identify an optimal stocking density. The three stocking densities were used at 30, 50, and 70 tilapia m-3 under three treatments with triplicate. The initial average weight of tilapia fingerlings at 32.31±9.59 g was stocked. Final weight, specific growth rate, and survival were significantly (p < 0.05) higher in the 30 tilapia m-3 stocking density than those in the 50 and 70 tilapia m-3 stocking densities. The best food conversion ratio of 1.47 was found in the 30 tilapia m-3 stocking density and followed by 2.0 and 2.90 in the 50 and 70 tilapia m-3 stocking densities, respectively. The production was comparable (p > 0.05) between the 50 and 70 tilapia m-3 stocking densities; however, the net profit was higher (p < 0.05) in the 50 tilapia m-3 stocking density group compared to the two other stocking density groups. This study suggests a stocking of density at 50 tilapia m-3 to increase Nile Tilapia O. niloticus productivity in the riverine cage culture system. Bangladesh J. Zool. 50 (2): 239-250, 2022

This study examined the intensification of mono-sex Nile tilapia Oreochromis niloticusaquaculturein riverine net cages installed at the River Dakatia, Roghunathpur, Chandpur. This study performed 120-day cage grow-out trials with densities of 50, 75, and 100 tilapia m-3 under three replications with an average initial weight of 28.92±8.37g per juvenile fish. The monthly water quality parameters (temperature, pH, dissolved oxygen, total alkalinity and hardness, ammonia-N and Nitrite-N) in the cage installation water area of the River Dakatia were found to be suitable for tilapia cage culture. The monthly average weight gain was significantly (p < 0.05) higher in 50 tilapia m-3 stocking density than in the other two stocking densities tested. The mean final weight and specific growth rate were significantly (p < 0.05) higher in 50 tilapia m-3 stocking densitythan the other two stocking densities. Significantly (p < 0.05) higher survival (97.92%) was found in the 50 tilapia m-3 stocking density group and followed by 86.74% and 84.39% in the 75 and 100 tilapia m-3 stocking densities, respectively. Consequently, the monthly relative and specific growth rate and feed conversion ratio were significantly (p < 0.05) higher in 50 tilapia m-3 stocking density fishes for the first, third, and fourth months. Gross production was comparable between 50 and 75 tilapia m-3 stocking densities but was significantly (p < 0.05) better than 100 m-3 stocking density. Net production was significantly (p < 0.05) higher at 50 tilapia m-3 stocking density group than those of 75 and 100 tilapia m-3 stocking densities. The best feed conversion ratio (1.60) was in the 50 tilapia m-3 stocking density group (p < 0.05) than those of 1.87 and 2.44 for the stocking of 75 and 100 tilapia m-3, respectively. Benefit-cost ratio and net profit were significantly (p < 0.05) better at 50 and 75 tilapia m-3 than at 100 tilapia m-3 stocking density. Therefore, considering maximum outputs, benefits, and performances, we recommend stocking density at 50 mono-sex tilapia m-3 for the best growth, cost-effective production, and highest-economic return from 120 days of grow-out net cages in the riverine culture system. J. Bangladesh Acad. Sci. 47(1); 43-52: June 2023