Effect of induced hyperoxia on the antioxidant status of Atlantic salmon Salmo salar L. fed three different levels of dietary vitamin E

Atlantic salmon smolt (64 g) were fed 40, 300 or 1100 mg kg(-1) all-rac-alp ha-tocopheryl acetate feed under normoxic and moderate hyperoxic conditions for 12 weeks. After 7 weeks, however, the hyperoxic fish were subjected to a temporary severe supersaturation of dissolved oxygen with development of gas bubble disease and substantial mortality as a result. Liver alpha-toco pherol (alpha-TOH) levels reflected the dietary input after 6 and 12 weeks of feeding. Increased levels of thiobarbituric-reactive substances (TBARS) in the liver of hyperoxygenated fish after 6 weeks indicate that moderate h yperoxic conditions may represent an oxidative challenge to the fish. After 12 weeks, liver ascorbic acid (AA) content was reduced in hyperoxygenated fish, and a decreasing tendency was also found in the liver content of alph a-TOH. Effects of oxygen supersaturation were also observed on liver antiox idant enzyme activities, content of glutathione and total mercapthans in li ver, phagocytic chemiluminescent response and total plasma protein level, i ndicating a disturbed redox balance. No effects of dietary vitamin E were o bserved on any of the measured parameters, indicating that high levels of d ietary vitamin E under these circumstances did not protect the fish against oxidative stress.