Optimization of stocking density and its impact on growth and physiological responses of Pangasianodon hypophthalmus (Sauvage, 1878) fingerlings reared in finger millet based biofloc system

A 90-day experiment was conducted to investigate the effect of different stocking densities on growth, physiological responses, and survival of Sutchi catfish (Pangasianodon hypophthalmus) fingerlings reared in finger millet based biofloc system (BFT). Sutchi catfish fingerlings (7.34 +/- 0.06 g) were stocked in five treatments (BFT-150/ m3, BFT-180/m3, BFT-210/m3, BFT-240/m3, and BFT-270/m3) in biofloc based units and a control (C-150/m3 with clearwater). All the five treatments and control were assigned in triplicate using 160 l plastic crates (100 l volume of water). Finger millet flour was used as an organic carbon source with 15:1C: N ratio. After 90 days of rearing, fingerlings were challenged with virulent Aeromonas hydrophilic. A significant increase in growth and feed utilization was observed in all the BFT treatments compared to the control. A similar trend coincided with the physiological responses. Digestive enzymes such as amylase, protease, and lipase and serum biochemical parameters (total protein, albumin, and globulin) were significantly improved in BFT treatments than in control. Anti-oxidant stress enzyme responses serum superoxide dismutase (SOD) and catalase (CAT) activity were significantly higher in BFT-150/m3 and lower value was recorded in BFT-270/m3. Metabolic enzyme response (liver and muscle tissues) was higher in BFT-270/m3 and C-150/m3, and substantially influenced by BFT with various stocking densities. Overall, BFT-270/m3 and C-150/m3 experimental units recorded lower growth performance, serum biochemical response, and higher metabolic enzyme activity. Relative survival percentages were significantly (p < 0.05)) better in BFT-150/m3 (66%) followed by BFT-180/m3 (63%) after challenge. The study revealed that application biofloc technology for Sutchi catfish fingerlings at stocking densities 210-240/m3 could be considered as optimum stocking density for better growth, physiological responses, and survival of Sutchi catfish fingerlings culture in biofloc system.