Iron catalyzed oxidation of trout diets and its effect on the growth and physiological response of rainbow trout

Two experiments were conducted to determine 1) the effect of iron supplementation and the quality of fish oils on dietary lipid peroxidation and 2) the concurrent effects of diet rancidity and iron overload on the growth and physiological response of rainbow trout. Semi-purified diets supplemented with graded levels of iron (0–6250 mg/kg diet as ferrous sulphate) were fed to trout for 12–36 weeks. The malonaldehyde (MA) concentration of the test diets increased as the iron levels in the diets increased indicating that iron catalyzed lipid oxidation was occurring. However, when ethoxyquin was added to the oils, the increase in dietary MA level was significantly reduced. Fish oils with an initial high peroxide value were more susceptible to iron-catalyzed lipid oxidation. The concurrent effects of diet rancidity and iron overload (greater than 86 mg/kg) led to the development of unique histopathological signs, poor growth and high mortalities in the trout. In contrast, when diet rancidity was low (less than 10 µg MA/g diet), the toxic level of dietary iron was greater than 1380 mg/kg diet. The concentration of iron in trout tissues, and the hematocrit and hemoglobin concentrations increased as dietary iron levels increased and were not affected by the degree of diet rancidity.