The vitamin E requirement of rainbow trout ( Salmo gairdneri) given diets containing polyunsaturated fatty acids derived from fish oil

Groups of rainbow trout (mean initial weight 14 g) were given diets containing 10% of fatty acids derived from a white fish offal oil together with graded levels of vitamin E (2–10 mg/100 g) for 16 weeks. Fish increased in weight by eight-fold over the course of the experiment but there were no differences in weight gain between treatments, food conversion was similar in all treatments, no pathologies were observed and few mortalities occurred. In trout given the lowest dietary vitamin E intake, tissue levels of vitamin E were lowest in skeletal muscle, concentrations in most other soft tissues were about threefold that in muscle but higher levels were found in brain. Increased erythrocyte fragility occurred in those fish given diets low in vitamin E, and ascorbic acid-Fe 3+-stimulated lipid peroxidation in liver microsomes decreased with increasing dietary vitamin E. Little or no malonaldehyde was formed in microsomes from trout fed diets containing 5 mg vitamin E/100 g or more. This was taken to be an adequate or safe concentration under the dietary conditions employed. Microsomes prepared from the muscle of trout given low levels (2 mg/100 g diet) of vitamin E were more susceptible to peroxidation in vitro than those obtained from gill, heart or liver. Microsomal susceptibility to peroxidation is determined by the ratio of vitamin E: peroxidizable unsaturated fatty acids in the microsomal membrane. Some of these ratios were measured and the results are discussed.