Culturing of fish at high stocking densities is a hallmark of biofloc aquaculture. Current work aimed to explore the influence of medium stocking densities of Nile tilapia (O. niloticus) i.e. 30, 40 and 50 fish/m3 on growth indices, carcass composition and microbial dynamics in biofloc system. Juvenile fish was reared for 180 days in tarpaulin sheet tanks having biofloc with feeding of 25% CP feed @ 3% of body weight per day. To maintain C/N ratio as 20:1, starch was used as carbon source. All the treatments showed significantly different response towards all parameters in question during the experiment. O. niloticus showed a gradual decrease in weight gain as stocking density increased. Best gain in weight (303.2g) was recorded at 30 fish/m3 density, while minimum (264.2g) at 50 fish/m3. Better FCR and survival of fish was also recorded for 30 fish/m3 density. Carcass analysis revealed a decline in crude protein (CP: 52.65 to 49.43%) and ether extract (EE: 24.49-23.36%) with increasing stocking densities 30 to 50 fish/m³, although dry matter (DM: 92.75 to 93.67%) and ash content (13.45 to 14.15%) increased. Water quality parameters viz. temperature, pH, nitrite-nitrogen (NO2), nitrate nitrogen (NO3), total ammonia-nitrogen (TAN) and total suspended solids (TSS) remained under optimal ranges. Maximum floc volume (20.76 ml/lit) was recorded in 50 fish/m3 treatment, while minimum (18.22 ml/lit) was observed at 30 fish/m3 treatment. Maximum concentrations (24.6×104 CFU/ml) of total heterotrophic bacteria in biofloc were observed at 50fish/m3 density, while minimum (15.3×104) concentrations were observed at 30fish/m3 density. Gut microbial community (CFU/g) were higher (35.5×107) at 50 fish/m3 whereas, lower value (28.2×107) were observed at 30 fish/m3. From the results of experiment, it is evident that varying stocking density of O. niloticus significantly affect the growth, carcass composition and microbial dynamics under biofloc culture.
Key words: Biofloc, Stocking Density, Nile Tilapia, Microbial Community, Water Quality, Carcass Composition