Dietary Alpha-Tocopherol Affects Tissue Vitamin E and Malondialdehyde Levels but Does not Change Antioxidant Enzymes and Fatty Acid Composition in Farmed Atlantic Salmon (Salmo salar L.)

In this study the effect of increasing dietary alpha tocopherol on vitamin E tissue concentrations, lipid peroxidation (malondialdehyde), antioxidant enzymes, and fatty acid composition has been investigated in farmed Atlantic salmon. To this end fish (initial body weight ~ 193 g, n = 70 per group) were fed diets based on fish oil (27.5 %), fish meal (15.0 %), wheat gluten (20.6 %), and soy protein concentrate (24.0 %) for 14 weeks. Diets were supplemented with 0 (negative control), 150, and 400 mg/kg vitamin E as all-rac alpha-tocopheryl acetate. Dietary vitamin E did not affect feed conversion efficiency ratio but significantly (p < 0.05) increased alpha-tocopherol concentrations in salmon plasma, liver, and fillet (n = 8 per group each). The increase in fillet alpha-tocopherol was accompanied by a considerable decrease (p < 0.01) in malondialdehyde concentrations at the higher supplementation level. Furthermore, we observed an antagonistic interaction between alpha- and gamma-tocopherol in plasma at the highest supplementation level, since high dietary alpha-tocopherol reduced plasma gamma-tocopherol concentrations. Liver antioxidant enzymes, including glutathione peroxidase and superoxide dismutase, remained largely unchanged in response to dietary alpha-tocopherol. Dietary alpha-tocopherol did not affect eicosapentaenoic acid and docosahexaenoic acid concentrations in salmon fillet. Present data suggest that alpha-tocopherol supplementations beyond dietary recommendations may further improve flesh quality and nutritional value of Atlantic salmon fillet as far as malondialdehyde and vitamin E concentrations are concerned.