Effects of dietary glutathione on the growth performance, skin mucus antioxidant capacity, and immune responses of juvenile taimen Hucho taimen

A 49-day feeding trial was conducted to examine the effects of dietary glutathione on growth performance, skin antioxidant capacity, immune responses, and gene expression in juvenile taimen (Hucho taimen). The experimental fish had a mean initial weight of 5.36 +/- 0.13 g and were fed diets (approximately crude protein 460 g/kg, gross energy 22 MJ/kg) containing graded amounts of glutathione (0-control, 100, 200, 400, and 800 mg/kg). Each group had 3 replicates with 500 fish per tank (500 L). Fish were fed four times daily until evident satiation. After the feeding trial, 60 fish from each tank were challenged with lipopolysaccharide for 7 days, and the skin mucus antibacterial activity, antioxidant ability, and skin gene expression were also determined. The weight gain (WG, 3642.33-3843.67 g) and survival rate (SR, 93.07-94.19%) were all significantly improved in fish fed dietary glutathione (100-800 mg/kg) compared with the control group (WG, 3414.30 g; SR, 90.61%) (P < 0.05). After a 7-day lipopolysaccharide (3.00 mg/kg body weight) challenge, compared with the control group, dietary glutathione (100-800 mg/kg) significantly increased skin mucus protein, lysozyme activity (LZM, 2.67-2.74 U/mg; control, 2.11 U/mg), alkaline phosphate activity (ALP, 5.09-5.34 U/L; control, 4.50 U/L), minimal inhibitory concentration (MIC, 100-200 mu L/mL; control, > 200 mu L/mL), and antimicrobial activity (7.72-9.11 mm; control, 7.19 mm) (P < 0.05). Furthermore, dietary glutathione (100-800 mg/kg) also improved skin mucus antioxidant capacity and superoxide dismutase (SOD, 9.45-9.52 U/L; control, 7.51 U/L), and glutathione peroxidase (GSH-px, 9.68-10.11 U/L; control, 8.68 U/L) was significantly higher (P < 0.05), whereas the malondialdehyde (MDA, 0.18-0.20 nmol/L; control, 0.23 nmol/L) concentration was lower (P < 0.05). Additionally, dietary glutathione (100-800 mg/kg) significantly decreased the expression levels of skin tumor necrosis factor (TNF-alpha), interleukin 1 beta (IL-1 beta), interleukin 6 (IL-6), and interleukin 8 (IL-8), but increased the expression levels of interleukin 10 (IL-10) and nuclear factor-kappa-B inhibitor alpha-like (I kappa B alpha). In conclusion, dietary glutathione (100-800 mg/kg) improved the growth performance and decreased the lipopolysaccharide-induced skin inflammatory response, indicating that glutathione has the potential for anti-inflammatory effects on juvenile H. taimen.