Effect of stocking density on the growth, body composition, and blood parameters of cage-reared Gangetic mystus catfish (Mystus cavasius)

Suitable stocking density of Gulsa tengra (Mystus cavasius) was observed by measuring growth performance, production, and survival in nylon net cages for 120 days in Chalan Beel floodplain ecosystem. Fry of Gulsha tengra (5.55 ± 0.49 g in weight) were stocked into 6 × 3 × 2-m (36 m3) floating net cages with treatments: T1-50, T2-100, T3-150, and T4-200 fry/m3 (in triplicates). The stocked fry was fed twice daily with commercial floating pellet containing 32 % protein at the rate of 5 % /fish body weight during the first 2 months and then reduced to 3 % for the next 2 months. The highest weight gain was observed in the lowest density treatment, T1 (18.70 ± 1.37 g) and the lowest (8.66 ± 0.99 g) in highest density treatment, T4 (all tests for significance were performed at a 5 % level). The rate of survival varied from 86.6 % and 95.8 %, with T1 resulting in the significantly highest survival. A better feed conversion ratio was also observed in T1 (1.75 ± 0.26). Significantly higher protein (16.86 ± 0.36) and fat (2.78 ± 0.02) contents were recorded in the fish body composition in T1. Water quality parameters (temperature: 26.0 ± 1.0 °C, pH: 7.2 ± 0.2, DO: 6.4 ± 0.1 mg/l, NH3-N: 0.002 ± 0.001) recorded throughout the study period were within the suitable range for fish culture. The highest red (119.0 ± 4.85 ×106 µl) and white blood cell (233.2 ± 16.02 ×103 µl), hemoglobin (5.65 ± 0.30 g/dl), total protein (5.50 ± 0.03 g/dl), albumin (1.82 ± 0.06 g/dl), and globulin (3.65 ± 0.15 g/dl) were also observed in T1 indicating optimum condition. Total and net production per cage were the highest in T1 with approximately 50 % increase (88.31 ± 6.72 and 59.27 ± 5.79 kg, respectively) compared to T4. The net income and benefit–cost ratio was increased by approximately 42 % and 30 %, respectively, in T1. Thus, this study recommended an optimal stocking density of 50 fish/m3 for Gulsha tengra to achieve a profitable and robust yield in cage culture