Effect of oxidized fish oil, vitamin E and ethoxyquin on the histopathology and haematology of rainbow trout, Salmo gairdneri Richardson.
Rainbow trout were fed for 24 weeks on practical diets containing varying concentrations of oxidized fish oil, with or without supplementation of vitamin E and ethoxyquin. Groups fed highly or extremely oxidized oils without DL-α-toxopherol acetate supplementation, and with or without supplemental ethoxyquin, exhibited lower red blood cell numbers, haemoglobin content, haematocrit, and increased haemolysis. In addition, fish from these groups had increased, abnormally developing polychromatocytes, splenic haemosiderosis and hepatic ceroidosis. The results indicate that vitamin E protects better and at lower concentrations than does ethoxyquin, and that supplementation with 33 mg of DL-α-tocopherol acetate/kg is adequate to prevent vitamin E deficiency signs when feeding diets containing 7.5% of a highly oxidized oil. Supplementation with ethoxyquin alone to diets containing highly oxidized oil appeared to exert partial protection, but did not increase the level of protection when added simultaneously with tocopherol acetate. The findings support the theory of a general antioxidant function for vitamin E, and suggest that death from vitamin E deficiency was due to the cumulative effects of liver dysfunction and anaemia.