Effect of different dietary protein levels on growth, carcass biochemical composition and apparent digestibility coefficient in juvenile Caspian trout (Salmo trutta caspius)

The effects of dietary protein levels were investigated on growth, carcass biochemical composition and apparent digestibility coefficient in Caspian trout, Salmo trutta caspius. The present study was carried out in a completely randomized design with five experimental diets containing five different dietary levels of protein: 35, 40, 45, 50 and 55%, and 15 fish per replication of each with an initial weight of 4.85 ± 0.45 g for 105 days.  Average oxygen concentration and water temperature were 7.6 ± 0.68 mg L-1 and 17.7 ± 1.5 °C, respectively, throughout the experimental period. Significantly higher final body weight, weight gain, specific growth rate, protein efficiency ratio and condition factor were observed in the fish fed diet with 40 and 45% protein compared to those fed on the 35 and 55 % protein diets. Feed efficiency ratio in treatments fed 35 and 55 % protein were significantly higher than those of fish fed 40 and 45% dietary protein levels (P≤ 0.05). Crude protein content increased with the increasing dietary protein levels, whereas crude lipid and moisture composition decreased with the increasing dietary protein levels. Therefore, it can be cocluded that increased levels of protein in the diets for juvenile Caspian trout (Salmo trutta caspius) up to 40 and 45% improved growth performance, feed utilization parameter and economic aspect.