Antioxidant status and nonspecific immune responses in rainbow trout (Oncorhynchus mykiss) fed two levels of vitamin E along with three lipid sources

Abstract

This study was designed to examine the effects of dietary vitamin E on antioxidant status and nonspecific immune responses of rainbow trout (Oncorhynchus mykiss) fed different lipids. Six semi-purified diets containing three lipid sources: pollock liver oil (PO), linseed oil (LO) and safflower oil (SO), each in combination with two levels of vitamin E (100 and 1000 mg α-tocopheryl acetate kg−1 diet), were fed to duplicate groups of 17 g fish for 9 weeks. The growth performances were significantly greater in the PO and LO groups compared to the SO fed fish, irrespective of vitamin E content. The hematocrit (Hct) values were also higher in the PO and LO fed fish suggesting that n−3 fatty acids in these oils were more involved in erythropoiesis. The red blood cells (RBCs) were less fragile in fish fed PO diets, regardless of vitamin E levels. The hydroperoxide content in red blood cells and superoxide dismutase (SOD) in plasma were slightly higher in fish fed 1000 mg vitamin E kg−1 diet suggesting that the antioxidant capacity of the vitamin at the high level was not evident compared to that at the lower level. On the other hand, only minor modulations of the immune responses related to vitamin E were observed for the three lipid groups. The total immunoglobulin (Ig) and phagocyte activity were lower while serum alternative complement and lysozyme activities, and the production of reactive oxygen species by head kidney leucocytes were higher in fish fed the higher amount of vitamin E. Although most of results in this study were not statistically significant, the prooxidant tendency of vitamin E observed at the high dose has to be examined carefully in relation to health of fish.