Stocking density as a driver of growth, health, water productivity and economic returns in biofloc-reared pengba, osteobrama belangeri (Valenciennes, 1844)

The present study evaluates the impact of varied rearing density on growth, survival, water quality, biochemical responses, economic returns and water productivity during the fry, fingerling and juvenile rearing of pengba, Osteobrama belangeri (Valenciennes, 1844) reared in a biofloc system. The spawn to fry rearing was conducted in 10,000 L for 28 days at varied densities (TS-1: 5000 m^{- 3}; TS-2: 7500 m^{- 3} and TS-3: 10000 m^{- 3}) and the fingerling (TF-1: 50 m^{- 3}; TF-2: 75 m^{- 3} and TF-3: 100 m^{- 3}) and juvenile (TJ-1: 20 m^{- 3}; TJ-2: 35 m^{- 3} and TJ-3: 50 m^{- 3}) were reared in 20,000 L circular tanks over 84 and 210 days, respectively. Water quality parameters remained within the acceptable ranges across all stages, although variations in temperature, dissolved oxygen and nitrogenous compounds were observed in few cases. Biochemical indices including serum glucose, serum protein, liver enzymes (SGOT, SGPT and ALP), and antioxidant enzymes (SOD and catalase) exhibited density dependent changes in fingerling and juvenile stages. Higher integrated biomarker response (IBR) scores observed in TF-3 and TJ-3. The growth performances significantly declined with increasing density during fry and fingerling rearing whereas juvenile growth remained insignificant with increment in stocking density. Survival was lower in fry (26.91-47.67%) followed by fingerlings (97.58-98.44%) and juveniles (94.7- 97.67%). Feed conversion ratio (FCR) and protein efficiency ratio (PER) trends indicated better feed utilization at lower density in fingerling and juveniles. Economic evaluation showed the highest net profit and benefit-cost ratio at TS-1 for fry and TF-3 and TJ-3 for fingerling and juvenile rearing. Water productivity indices (TWPI and CWPI) in fry rearing varied significantly (P > 0.05) at TS-3. In contrast, fingerling and juvenile stages showed increased productivity with higher stocking densities.