EFFECTS OF DIETARY PROTEIN LEVELS ON GROWTH PERFORMANCE, BODY COMPOSITION, LIVER BIOCHEMICAL INDICES, AND DIGESTIVE ENZYME ACTIVITIES OF JUVENILE CHINESE CRUCIAN CARP

The study was conducted to evaluate the effects of dietary protein levels on evolution, body composition, liver biochemical indices, as well as digestive enzymes activities of juvenile Chinese crucian carp. Six isolipidic and isoenergetic diets were formulated containing 30.18%, 33.13%, 36.16%, 39.34%, 42.32%, and 45.46%, respectively. A total of 540 juvenile Chinese crucian carp with the average initial weight of (3.10 ± 0.01) g were randomly distributed into six groups with three replicates per group, containing 30 juvenile Chinese crucian carp per replicate, which were fed for eight weeks. The results indicated that with the increase of dietary protein level, the weight gain rate (WGR), specific growth rate (SGR), feed efficiency (FE), protein efficiency ratio (PER), the whole body protein content (WBPC), the hepatic glutamic-pyruvic transaminase (GPT), and intestinal trypsin (TPS) activities of fish in 36.16% group were significantly higher than those in other groups (P<0.05). The hepatic total cholesterol (HTC) and triglyceride (TG) content of fish in 30.18% group were remarkably higher than those in other groups except for 33.13% group. Based on the quadratic regression analysis of theSGR, PER, and dietary protein levels, it was revealed that the rate of optimal dietary protein for Chinese crucian carp ranges from 35.29% to 37.07% under the experimental condition.