Research on feed protein requirement of Cyprinus carpio haematopterus

Yellow River carp (Cyprinus carpio haematopterus) is a unique and important freshwater economic fish whose demand for feed protein is lower than that of other carps. In order to explore the adaptation and utilization ability of Yellow River carp to different dietary protein contents in terms of growth traits, immunity and metabolism, we fed the yellow carps of initial body mass of (360.22±1.02) g with test diets with protein contents of 22.63% (D1), 25.32% (D2), 28.15% (D3), 31.43% (D4) and 34.18% (D5). The results show that the weight gain rate, specific growth rate and protein efficiency were highly significantly higher in D3 group than in the other groups (p<0.01), and the feed coefficient was significantly lower in D3 group than in the other groups (p<0.05). Relative expression of growth genes GH, IGF-1 and protein synthesis genes TOR, 4EBP2 were significantly higher in D3 group than in D1, D4 and D5 groups (p<0.05). Serum biochemistry levels of glutamic and glutamic aminotransferase were significantly lower in D3 group than in D1 and D5 groups, but alkaline phosphatase levels were significantly higher in D1 and D5 groups (p<0.05). The enzyme activities of α-amylase, lipase, trypsin, superoxide dismutase, catalase, etc. And the content of reduced glutathione in D3 group was significantly higher than those in D1 and D5 groups (p<0.05), and malondialdehyde was highly significantly lower in D3 group than in the other groups (p<0.01). The relative expressions of Rhag, Rhbg and Rhcg1 among ammonia metabolism genes were significantly higher in D5 group than in other groups (p<0.05). The fit regression analysis shows that the optimal dietary protein requirement of Yellow River carp is about 28.57%−29.04%.