Changes in tissue α-tocopherol status and degree of lipid peroxidation with varying α-tocopheryl acetate inclusion in diets for the African catfish

Juvenile African catfish, Clarias gariepinus (Burchell), were fed low-tocopherol, practical test-diets containing graded levels of alpha-tocopheryl acetate (0, 80, 200 and 500 mg kg(-1) dry feed) at proportionately 0.02 body weight per day for 70 days. After the feeding period, selected fish tissues were assayed for alpha-tocopherol and thiobarbituric acid reactive substances (TBARS) concentrations, before and after iron-ascorbate stimulated peroxidation. Results show that tissue accretion of alpha-tocopherol in muscle, liver and blood plasma increased linearly (R-2 = 0.83, 0.82 and 0.93, respectively) in response to elevated dietary supplementation of alpha-tocopheryl acetate within the range of doses under study. In muscle and liver this resulted in a significant decrease (P < 0.05) in basal TBARS and TBARS after stimulated peroxidation, indicating a greater stability against oxidation. Growth indices were not significantly affected (P > 0.05) by dietary alpha-tocopheryl acetate inclusion. Clarias fed the highest alpha-tocopheryl acetate dose (500 mg kg(-1) dry feed) were observed to have significantly lower (P < 0.05) haematocrit (% packed cell volume) than fish fed the basal diet (0 mg kg(-1) dry feed). It was concluded that supplemental alpha-tocopheryl acetate in practical diets, for Clarias gariepinus, was effective in reducing the degree of tissue-lipid peroxidation under conditions of increased oxidative stress. Thus, the post mortem resistance to oxidation achieved would improve the stability of catfish products destined for human consumption.