Diet with optimal glutathione supplement improves growth, nonspecific immunity, intestinal microbiota, and antioxidant ability in Micropterus salmoides.

In this study, Micropterus salmoides were fed with dietary glutathione (GSH, 0, 100, 300, and 500 mg/kg) for 56 days to investigate its effects on growth performance, serum nonspecific immunity, liver antioxidant capacity, tissue morphology, and intestinal microbiota. The results showed that the survival rate, weight gain rate, and specific growth rate and condition factor increased, whereas the feed conversion ratio, hepato-somatic index, and viscerosomatic index decreased in the GSH groups. Compared with the control group, the serum total protein content significantly increased, whereas the triglyceride and total cholesterol significantly decreased in the 300-mg/kg dietary GSH group. The activities of lysozyme, alkaline phosphatase, and acid phosphatase were significantly higher in GSH-supplemented groups, peaking at 300-mg/kg GSH. GSH supplementation significantly increased total antioxidant capacity and decreased malondialdehyde content, with the most pronounced effects at 300-mg/kg GSH. Further antioxidant indicators showed that a dietary supplement of 300-mg/kg GSH significantly increased the activities of superoxide dismutase, glutathione transferase, endogenous glutathione, glutathione reductase, and catalase. At 300-mg/kg GSH, the liver exhibited improved characteristics with alleviated vacuolation and hepatocyte nuclear shift, and intestine showed enhanced structure with increased villus height and intestinal wall thickness. Additionally, a 300-mg/kg GSH supplementation improved the diversity of intestinal microbiota, increased the abundance of probiotics such as Bacillus, and inhibited the development of pathogenic bacteria such as Plesiomonas. Overall, the results suggest that the effect of GSH addition on improving growth performance, nonspecific immunity, antioxidant capacity, and intestinal microbiota of M. salmoides is best in the 300-mg/kg addition group. Based on second-degree polynomial regression analysis of weight gain, the optimum requirement of dietary GSH in M. salmoides is a 336.84-mg/kg diet.