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The aim of this study was to investigate the underlying hepatoprotective effects of yeast culture (YC) against carbon tetrachloride (CCl 4 )-induced hepatic damage in Pseudobagrus ussuriensis. The fish were randomly divided into three experimental groups (Control, CCl 4 and YC+CCl 4 ) with three replicates of 30 fish in each replicate.Firstly, the Control and CCl 4 groups were fed basal diet without yeast culture, and the YC+CCl 4 group was fed diet with 20 g/kg YC for 8 weeks. After the end of feeding experiment, Control group was intraperitoneally injected olive oil with 0.05 ml/15 g fish body weight, while CCl 4 and YC+CCl 4 groups were intraperitoneally injected CCl 4 olive oil solution (CCl 4 : olive oil = 3:7) with 0.05 ml/15 g fish body weight for 48 h. The results indicated that fish fed with 20 g/kg yeast culture not only ameliorated injured hepatic cell, as evidenced by well-preserved liver architecture, but also significantly decreased plasma AST activity in the CCl 4 -induced hepatic injury model. Next, we found that dietary 20 g/kg YC supplementation could improve hepatic antioxidant activity and inhibit lipid peroxidation induced by CCl 4 . Fish fed 20 g/kg YC could suppress the decrease of plasma IgM and plasma ACH50 content caused by CCl 4 (p < .05).In addition, we also found that fish treated with CCl 4 up-regulated the expression of immune-related genes (TLR2, MyD88 and NF-κBp65), proinflammatory cytokines (IL-1β and IL-8) and Hsp70 mRNA expression in liver compared with the Control group; meanwhile, fish fed with 20 g/kg YC down-regulated the above-mentioned genes expressions in liver compared with CCl 4 group. In general, the results mentioned above suggested that the dietary yeast culture could relieve the oxidative stress, immune damage and liver injury induced by CCl 4 and could also suppress CCl 4 -induced inflammation through inhibiting the TLR2/NF-κB signalling pathway.

An 8-week feeding trial was conducted to evaluate the effects of dietary yeast culture (YC) supplementation on growth performance, antioxidant activity, nonspecific immunity, and disease resistance of Pseudobagrus ussuriensis (average initial weight 6.01 ± 0.01   g ). Four isonitrogenous and isolipidic diets were formulated to contain 0 (Y0), 10 (Y1), 20 (Y2), and 30 (Y3) g/kg YC, respectively. After the feeding experiment, the challenge test of injecting Aeromonas hydrophila was executed. Results showed that appropriate YC supplementation level in the diet could improve growth performance, digestive enzyme activities, nonspecific immunity capacity, antioxidant capacity, and disease resistance of P. ussuriensis. And the highest weight gain, feed intake, specific growth rate, and IGF-1 gene expression level were observed in fish fed the Y2 diet. The activities of protease and amylase in intestine in fish fed the Y2 diet were enhanced compared with that in fish fed the Y0 diet significantly ( P < 0.05 ). Simultaneously, fish fed the Y2 diet had significantly higher serum lysozyme activity and significantly lower serum alanine amino transferase activity ( P < 0.05 ). Dietary 20 g/kg YC supplementation increased the activity of catalase and total antioxidant capacity in liver and reduced malondialdehyde content in the liver and intestine of P. ussuriensis significantly ( P < 0.05 ). Fish fed the Y2 diet had the highest disease resistance under the condition of A. hydrophila challenge ( P < 0.05 ). The quadratic regression analysis based on weight gain against dietary YC levels indicated that the appropriate dietary YC supplementation level is 13.4 g/kg diet.