The effect of biofloc system on water quality, growth performance, immunity and body composition of Nile tilapia (Oreochromis niloticus) at different densities in brackish water

An experiment was conducted to evaluate the effect of biofloc system on water quality, growth performance, immunity and body composition of Nile tilapia at different stocking densities. Fry (3.2±0.05 g) stocked in 500 and 1000/m3 in biofloc and clear water system (as control) in three replicates and reared for 50 days. Results showed that the lowest TAN and highest nitrite and nitrate were observed in BFT treatments. Total suspended solid, floc volume and bacteria increased by increasing stocking density. Maximum final weight (12.9g), SGR (3.21 %/day), survival (100%) and the best FCR (0.91) were obtained in BFT (500/m3). There were no significant differences in survival among treatments (p>0.05). Lysozyme, immunoglobulin and catalase of fishes in the biofloc treatments were significantly (p<0.05) better than control. Proximate analysis revealed that protein and lipid content of fishes in BFT were slightly higher than control groups but these differences were not significant. It seems that although fishes in BFT 500/m3 statistically showed better indices than others but due to small differences in growth indices and feed conversion ratio in one hand and no difference in survival rate between 500 and 1000/m3. On the other hands, the study suggests the stocking density of 1000/m3 for larviculture of tilapia in biofloc system to use water and equipment more efficiently.