THE QUANTITATIVE REQUIREMENT FOR ALPHA-TOCOPHEROL BY JUVENILE AFRICANCATFISH, CLARIAS-GARIEPINUS BURCHELL

Employing practical-type diets containing graded levels of all-rac-alp ha-tocopheryl acetate (0, 5, 15, 30, 45, 60, 75 or 100 mg/kg), the qua ntitative requirement for alpha-tocopherol by juvenile African catfish (Clarias gariepinus Burchell) was investigated. Diets, defined with r espect to selenium, fatty acid and ascorbate inclusion, were offered f or 12 weeks during which catfish grew from 10 g to 120 g. Dietary regi me had no significant effect on growth (P > 0.05), although haematocri t values increased with increasing tocopherol dose above 25 mg/kg (ass ayed) (R-2 = 0.71, P < 0.05). Tissue accretion of the vitamin increase d concomitant with dietary dose (P < 0.001). Employing a colorimetric assay for thiobarbituric acid reactive substances (TBARS) it was evide nt that concentration of TBARS in muscle and liver reflected tissue ox idation status, in that elevated dietary vitamin E resulted in decreas ed assayed TBARS (P < 0.05). By broken-line analysis the requirement f or this species to suppress lipid peroxidation was estimated as 30 to 40 mg all-rac-alpha-tocopheryl acetate per kg dry diet and this agrees with published requirements of many fish species.