Effect of stocking density and source of animal protein on growth and survival of rainbow trout fingerlings in flow-through system at Nuwakot, Nepal

An experiment was conducted in outdoor nursing raceways with flow-through system (2.7 m2) at the Fisheries Research Station, Trishuli, Nuwakot Nepal for 249 days to evaluate the effect of stocking density and sources of animal protein on growth and survival of rainbow trout fingerlings production. The experiment was conducted in 2 × 2 factorial completely randomized design having two stocking densities, (density-1: 10 kg/m2 and density-2: 12.5 kg/m2) and two diets (diet-1: shrimp meal based diet and diet-2: 5% bovine blood meal mixed diet). All treatments were replicated thrice. Water from the Trishuli river was used and 50 cm water depth was maintained in all treatments. Initial feeding rate of 10% of the body weight was gradually reduced to 8, 7, 6, 5, 4 and 3% was maintained for the subsequent months. Feeding was done 5 times a day throughout the study period. Results showed that the mean total harvest weight in diet-1 (30.17 ± 1.34 kg) was significantly higher than in diet-2 (22.77 ± 1.34 kg); however, no significance difference was observed at stocking density levels. Mean survival of fish in diet-1 (60.30 ± 2.08%) was significantly higher than diet-2 (47.78 ± 2.08%). Similarly, survivability of fish in density-1 (63.45 ± 2.08%) was significantly higher than in density-2 (44.63 ± 2.08%). The mean dissolve oxygen at density-2 (8.89 ± 0.02 mg/L) was significantly lower to that of density-1 (8.94 ± 0.02 mg/L) and B:C ratio was high with shrimp meal based diet and high stocking density (T3). In the present study, the treatment with shrimp meal based diet and high stocking density (T3) was superior with high mean total harvest weight, gross fish yield, low FCR and high B: C ratio than other treatment combinations. The present study demonstrated that growth, production and survival performances of rainbow trout in the present experimental condition were not satisfactory by substituting a part of shrimp meal by blood meal.