Optimum dietary protein requirement for maximum growth performance of Caspian kutum (Rutilus frisii) juveniles

A 12-weeks feeding trial was conducted to estimate the optimum dietary protein level of Caspian kutum white fish as one of the highly important commercial species in the south of the Caspian Sea. The fish juveniles (0.59±0.05g body weight) were randomly distributed into 21 aquariums (30 fish per aquarium). The fish were fed with seven experimental diets containing 28, 32, 36, 40, 44, 48, and 52 % crude protein (CP). Results showed that dietary protein levels significantly (p<0.05) affected growth performance and feed utilization of Caspian kutum juveniles. The fish fed a diet with 40% CP showed higher survival rate (p<0.05) than other groups. Feeding the fish with diets at 40-44% CP improved the weight gain (WG) and specific growth rate compared to 28%, 32%, and 52% CP diets. The feed conversion ratio and protein productive value were promoted by increasing the dietary CP level, while the protein efficiency ratio was decreased in diets containing high CP levels (44-52%). The fish receiving the protein supplemented diets showed higher protein and lipid content than the initial fish population. The results indicated that dietary CP level only affected the body protein content of the Caspian kutum juveniles (p<0.05). A broken-line regression calculated the protein requirement at 42.85-43.23 % based on the WG and PPV (protein productive value).