EFFECTS OF ENZYMATIC HYDROLYZED SOYBEAN MEAL ON GROWTH PERFORMANCE, LIVER FUNCTION AND METABOLISM OF LARGEMOUTH BASS (MICROPTERUS SALMOIDES)

To investigate the effects of enzymatic hydrolyzed soybean meal (ESBM) on growth performance, liver function and metabolism of largemouth bass (Micropterus salmoides), five isonitrogenous and isoenergetic diets were formulated by replacing fish meal with a plant-based protein source compound (enzymatic hydrolyzed soybean meal: corn gluten meal=10 鲶1) for a 67-days trial. The additions of ESBM in the feed were 0 (E0), 15% (E15), 20% (E20), 25% (E25), 30% (E30) to replace 0, 23.64%, 30.91%, 40%, 47.27% of the fish meal, respectively. In additional, two diets of soybean meal (SBM) and fermented soybean meal (FSBM) were used as the substitute for 20% ESBM, respectively. The results showed that the specific growth rate and weight gain rate of E25 and E30 were significantly higher than those of other groups (P<0.05), and that the feed coefficient ratio of each group had no significant difference (P>0.05). The survival rates of the E25 and E30 groups were lower than other groups. With the increase of ESBM, the viscerosomatic index, hepatic index and the lipid content of body decreased significantly (P<0.05). The specific growth rate of FSBM group was significantly lower than that of E20 group (P<0.05), and viscerosomatic index and hepatic index of FBSM were significantly higher than those of SBM and E20 (P<0.05). The activities of amylase and lipase of intestines increased first and then decreased with the increased ESBM, which were significantly higher than that of the control group (P<0.05). The activity of pepsin in E20 and E30 group was significantly higher than that of the control group (P<0.05). The activity of amylase in FSBM group was significantly higher than SBM and E20 (P<0.05), while the change of intestinal lipase activity was opposite. The activities of liver total-antioxidant capacity (T-AOC), glutamic oxaloacetic transaminase (AST) and alanine aminotransferase (ALT) in all group except liver ALT in E30 group were significantly induced by ESBM (P<0.05), and ESBM significantly reduced liver malondialdehyde (MDA) (P<0.05). The liver MDA content and ALT activities of FSBM group was significantly lower than SBM and E20 group (P<0.05), and the liver AST activity was in the order of E20>FSBM>SBM. The oxygen consumption increased significantly with the increased ESBM, and the nitrogen excretion in E20, E25 and E30 were significantly higher than E0 group (P<0.05). The muscle nitrogen retention rates of E20 and E30 were higher than other groups. ESBM had significant effects on serum free fatty acid (NEFA), total cholesterol (T-CHO), triglyceride (TG), and low density lipoprotein cholesterol (LDL-C) of largemouth bass. Among E20, FSBM and SBM groups, the oxygen consumption in FSBM group was significantly lower than other two groups (P<0.05), while nitrogen excretion was opposite. The serum T-CHO of SBM group was significantly higher than other two groups (P<0.05), while serum LDL-C and muscle lipid were the contrary trend. The serum TG of E20 group was significantly lower than other two groups (P<0.05). These results indicated that the addition of ESBM up to 30% did not harm the growth, and reduced liver oxidative stress to enhance nutrients metabolism. All FSBM, SBM and ESBM have benefits to replace 30.91% fish meal with the best effects by ESBM.