EFFECTS OF LOW-PROTEIN DIET ON GROWTH PERFORMANCE, BODY COMPOSITION, TRANSAMINASE ACTIVITY AND ANTIOXIDANT CAPACITY OF YELLOW CATFISH HYBRID

High protein content easily leads to nutrient imbalance in feed, reduces the efficiency of digestion and utilization of nutrients in fish, and increases the discharge of pollutants in aquaculture. It not only increases feed cost, but also easily causes water environment pollution. Reducing feed protein level can effectively reduce ammonia nitrogen emission in animal feces, but it may lead to the degradation of animal production performance. Supplementation of restricted amino acids can improve the protein utilization rate of animals and also reduce the nitrogen emission in the breeding process. Yellow catfish (Pelteobagrus fulvidraco) is a benthic small economic fish with a large aquaculture yield. This experiment with yellow catfish hybrid larvae as the research object, explore the supplemental methionine and lysine of low protein feed for yellow catfish hybrid larvae growth performance, body composition, transaminase activity and the influence of antioxidant capacity, to cross the yellow catfish hybrid nutrition requirements and related research, and health breeding to provide theoretical basis and reference. In this study, five experimental diets were formulated and there were three protein levels as 42% (control), 37% (LP1) and 32% (LP2). By using the control diet as standard, other two low-protein diets (37% and 32%) and supplementation with lysine and methionine (LP1+AA and LP2+AA) were formulated. Each diet was fed to triplicate groups of fish for 8 weeks, and the initial weight of fish was (0.96±0.01) g. At the end of the experiment, the growth performance, body composition, transaminase activity and antioxidant capacity of yellow catfish hybrid were measured. The results showed that compared with the control group, (1) the weight gain rate and specific growth rate of yellow catfish hybrid in LP1 group and LP2 group reduced significantly (P<0.05). There was no significant difference in weight gain rate and specific growth rate between LP1+AA and LP2+AA yellow catfish hybrid (P>0.05). (2) The relative expression levels of GH, IGF-1 in pituitary and GH in hypothalamus of yellow catfish hybrid in LP2 group and LP2+AA group decreased significantly (P<0.05), and there was no significant difference between the other groups with control group (P>0.05). (3) There was no significant difference in water content, crude protein, crude fat and crude ash content between muscle and whole fish in each experimental group (P>0.05). (4) There was no significant difference in AST activity in liver and serum among all the groups (P>0.05), and serum ALT activity in LP2 group was significantly higher than that in the control group and LP1+AA group (P<0.05). (5) CAT activity in serum, T-AOC, Cu/Zn-SOD, Mn-SOD and CAT mRNA relative expression in liver of both LP2 and LP2+AA groups decreased, and ROS content in liver and serum increased. There were no significant differences in SOD, CAT, T-AOC, MDA and ROS in liver and serum and Cu/Zn-SOD, Mn-SOD and CAT mRNA relative expression in liver of LP1+AA groups (P>0.05). These results showed that reducing the protein content of both 5% and 10% in the feed would negatively affect the growth performance and antioxidant capacity of yellow catfish hybrid. Reducing the protein content of the feed by 5% and adding lysine and methionine would not significantly affect the growth performance and antioxidant capacity of yellow catfish hybrid. Therefore, we suggest that the protein content in feed can be reduced by supplementing amino acid in feed production.