This study examined the effect of dietary lipid oxidation on Arctic charr and Nile tilapia. Primary dietary lipid oxidation reduced growth of Arctic charr. In Arctic charr, the activities of Catalase and glutathione peroxidise increased with lipid oxidation. Growth of Nile tilapia increased with dietary lipid oxidation. Differences in lipid intake and access to vitamin E/tocopherol affect the tolerance of fish to lipid oxidation.