Requirement for alpha-tocopherol by channel catfish fed diets low in polyunsaturated triglycerides

Channel catfish (Ictalurus punctatus) were grown from 5 to 45 g average size by feeding diets containing a low level of polyunsaturated fatty acids (0.48% linolenic acid) and supplemented with 0 (basal), 25, 75, 250 or 2500 mg/kg of alpha-tocopherol or 125 mg/kg of ethoxyquin. Growth rate was improved by supplementation of the basal diet with ethoxyquin (P less than 0.05) and further improved by supplementation with alpha-tocopherol (P less than 0.05); increasing alpha-tocopherol above the lowest level did not improve growth. Fish fed the basal diet were lighter in color, visibly thinner across the back, more easily excitable and had lower hematocrits. Histological signs in the alpha-tocopherol-deficient fish included extreme atrophy and necrosis of white muscle fibers, sclerotic glomeruli in the posterior kidney and ceroid-laden macrophages in intrahepatic blood vessels. Fish fed the lowest level of alpha-tocopherol showed no gross signs of vitamin deficiency but histological examination revealed necrosis of white muscle fibers and ceroids in liver blood vessels. No pathological changes were found in fish fed higher levels of alpha-tocopherol. These results indicate that high amounts of polyunsaturated fatty acids are not necessary in alpha-tocopherol-deficient diets to produce myopathy in channel catfish, and that the present National Research Council requirement for this vitamin for channel catfish may be low.