Effects of Yeast Hydrolysate on Growth, Immunity, Oxidation Resistance, and Anti-Streptococcus agalactiae Activity of Genetically Improved Farmed Tilapia

Abstract:

This study aimed to investigate the effects of yeast hydrolysate on the growth performance, immunity, oxidation resistance, and anti-Streptococcus agalactiae activity of genetically improved farmed tilapia (GIFT). Five experimental diets were prepared by adding 0 (control group), 0.5%, 1.0%, 1.5%, and 2.0% yeast hydrolysate to the basic diet of these fish. GIFT with an initial weight of (25.80±0.45) g were randomly divided into five groups and were cultured for 8 weeks. After the breeding test, 12 fish from each group were selected for the S. agalactiae challenge test. Each fish was injected intraperitoneally with 0.2 mL bacterial solution at a concentration of 8.3×105 CFU/mL, and the cumulative mortality was counted for 14 days. The results showed that the final body weight and specific growth rate (SGR) increased significantly at first (P<0.05) and then decreased with the increase in the concentration of yeast hydrolysate. Regression model analysis showed that the most suitable dietary yeast hydrolysate level reached the highest SGR at 1.29%. The activities of nitric oxide synthase, phenol oxidase, acid phosphatase, catalase, and superoxide dismutase increased (P<0.05) at first and then decreased under the increased dietary yeast hydrolysate level; the peak was reached on supplementation with 1.5% yeast hydrolysate. Dietary yeast hydrolysate significantly influenced the resistance of GIFT to S. agalactiae (P<0.05). Except for the 0.5% yeast hydrolysate test group, the cumulative mortalities of the other test groups (1.0% yeast hydrolysate supplementation or more) were significantly lower than the cumulative mortality of the control group (P<0.05). In this study, the addition of yeast hydrolysates to the diet of GIFT significantly improved their growth performance, immunity, and disease resistance, and the 1.5% yeast hydrolysate-supplemented test group showed the best results.