Effects of dietary reduced glutathione on growth performance, non-specific immunity, antioxidant capacity and expression levels of IGF-I and HSP70 mRNA of grass carp (Ctenopharyngodon idella)

• Dietary GSH could promote the growth of fish, improve survival rate and lower FCR.
• Dietary GSH could increase non-specific immunity, antioxidant capacity, and expression levels of IGF-I and HSP70 mRNA.
• Dietary GSH could enhance the resistance of fish to pathogen infection.
• Dietary excess GSH had negative effect on fish.

This study was conducted to evaluate the effects of dietary reduced glutathione (GSH) on growth performance, non-specific immunity, antioxidant capacity and related gene expression of grass carp (Ctenopharyngodon idella). Six hundred and thirty juvenile grass carp with initial body weight of 5.10 ± 0.09 g were randomly distributed into six groups with three replicates each, fed six diets containing graded levels of GSH (14.26, 112.41, 210.24, 407.45, 602.85 and 798.32 mg/kg diet) for 60 days. At the end of the feeding trail, ten fish per tank were challenged with Aeromonas hydrophila and the cumulative mortalities were recorded for 7 days. The results showed that the weight gain (WG), specific growth rate (SGR) and survival rate of grass carp, serum total protein (TP), lysozyme, alkaline phosphatase (ALP), and complement 3 (C3) levels, activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) in the liver, and liver total antioxidant capacity (T-AOC) and GSH contents, and expression levels of IGF-I and HSP70 mRNA significantly increased, while feed conversion rate (FCR), liver glutathione reductase (GR) activity and malondialdehyde (MDA) content significantly decreased with dietary GSH levels up to 407.45 mg/kg diet (P < 0.05), whereas dietary excess GSH had a negative effect on the above parameters. However, activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST), and GSH content in serum were not significantly affected by dietary GSH contents among all groups (P > 0.05). The challenge experiment showed that the cumulative mortality significantly decreased with dietary GSH contents up to 407.45 mg/kg diet (P < 0.05), and then increased. Thus, the diet supplemented with a certain amount of GSH could promote the growth of juvenile grass carp, improve survival rate and lower FCR, increase non-specific immunity, antioxidant capacity, and expression levels of IGF-I and HSP70 mRNA, and enhance the resistance to pathogen infection. However, dietary excess GSH had negative effect on fish. Based on second-degree polynomial regression analysis of weight gain, the optimum requirement of dietary GSH in juvenile grass carp is 381 mg/kg diet.