Administration of grape (Vitis vinifera) seed extract to rainbow trout (Oncorhynchus mykiss) modulates growth performance, some biochemical parameters, and antioxidant-relevant gene expression

Grape seed, as a main source of polyphenols, has many nutritional and medicinal properties in humans. In the current study, the effects of dietary ethanolic grape seed extract (GSE) on the growth performance, antioxidant activity, and some biochemical parameters in rainbow trout were investigated. Ninety fish (initial weight 78.47 g) were randomly distributed among nine cement tanks (1.8 m × 0.22 m × 0.35 m) with 10 fish per tank. Three experimental diets containing either 0, 10, or 50 g kg^-1 GSE were prepared and each diet was randomly assigned to three tanks of fish for 60 days. Results showed that feeding GSE enhanced some growth parameters including the specific growth rate and condition factor in comparison with the control group. Among different serum metabolites, the glucose levels in treatment groups significantly decreased compared to the control group. The total product of lipid peroxidation indicated as malondialdehyde significantly decreased in both the GSE-added treatment groups. The gene expression related to the antioxidant enzymes, catalase, glutathione peroxidase 1, and glutathione S-transferase A, were upregulated in the intestine of fish that received a low dose of GSE. The results of the current study suggest that GSE, especially at 10 g kg^-1, diet had the potential to improve (1) specific growth rate and condition factor, (2) biochemical parameters including glucose and lipid peroxidation product, and (3) upregulated the expression of antioxidant genes including catalase, glutathione peroxidase 1, and glutathione S-transferase A in rainbow trout.