Effects of dietary reduced glutathione on the growth and antioxidant capacity of juvenile Atlantic salmon ( Salmo salar )

To investigate the effects of dietary reduced glutathione (GSH) on the growth performance and antioxidant capacity of juvenile Atlantic salmon (Salmo salar), 396 juvenile fish with initial body weight of 143.07 +/- 6.56 g were randomly distributed into four groups fed four diets with graded supplementation levels of GSH (0, 100, 200 and 400 mg/kg diet) for 83 days. The results showed that the appropriate GSH supplementation (100 and 200 mg/kg diet) significantly increased the growth performance, activities and gene mRNA expression levels of glutathione peroxidase (GPx) and glutathione transferase (GST), and the content of GSH and total antioxidant capacity (TAOC), whereas it significantly decreased activities and gene mRNA expression levels of superoxide dismutase (SOD) and catalase (CAT), and the content of malondialdehyde (MDA; p < 0.05). However, the excess dietary GSH (400 mg/kg diet) had an adverse effect on the all above indexes. Interestingly, the dietary GSH had the opposite effect on GSH-related antioxidant enzymes (GPx and GST) and other antioxidant enzymes (SOD and CAT). The results showed that the diet with 200 mg/kg GSH supplementation was optimal for the juvenile Atlantic salmon, which had a measured GSH content of 209.54 mg/kg.