This study was conducted to determine the dietary vitamin E requirement of juvenile hybrid striped bass (Morone chrysops female × Morone saxatilis male). Semi‐purified diets supplemented with 0.2 mg Se kg−1 from Na2SeO3 and either 0 (basal), 10, 20, 40, 60, or 80 mg vitamin E kg−1 as DL‐α‐tocopheryl acetate were fed to hybrid striped bass initially averaging 1.8 ± 0.1 g (mean ± SD) for 12 weeks. Fish fed the basal diet, which contained 5.8 mg α‐tocopherol kg−1 dry weight, were darker in colour and had reduced weight gain, as well as generally reduced haematocrit values compared with fish fed diets supplemented with vitamin E. In addition, fish fed diets containing less than 20 mg supplemental vitamin E kg−1 had significantly (P < 0.05) reduced weight gain and feed efficiency compared with those fed diets supplemented with vitamin E at 20–80 mg kg−1. Dietary supplementation of vitamin E caused incremental increases in the concentration of α‐tocopherol in both plasma and liver tissues. However, hybrid striped bass fed graded levels of vitamin E did not exhibit a dose response in terms of ascorbic acid‐stimulated lipid peroxidation of hepatic microsomes. Regression analysis of weight gain data using the broken‐line model indicated a minimum vitamin E requirement (± SE) of 28 (± 3) mg kg−1 dry diet. Based on these data, the dietary vitamin E requirement of hybrid striped bass appears to be similar to that determined for other fish species.

A feeding trial was conducted to determine the minimum dietary vitamin C requirement of juvenile red drum and characterize signs of vitamin C de®ciency. Semipuri®ed diets containing 400 g crude protein kg ±1 from lyophilized red drum muscle and crystalline amino acids were used in the feeding trial. The basal diet without supplemental vitamin C contained » 6 mg vitamin C kg ±1 and was fed for a 1-week conditioning period. Red drum, initially averaging » 3.6 g each, were fed diets supplemented with 0, 10, 20, 30, 45, 60, 75, or 150 mg vitamin C kg ±1 as ascorbate polyphosphate for a period of 10 weeks. Fish fed the basal diet began to exhibit overt signs of vitamin C de®ciency, including reduced weight gain, lordosis, scoliosis and loss of equilibrium after 8 weeks. Total ascorbate was undetectable in liver of ®sh fed the basal diet while liver ascorbate levels in ®sh fed the other diets generally re¯ected dietary supplementation. Regression analysis of weight gain data using the broken-line model resulted in a minimum vitamin C requirement (SE) of 15 3 mg kg ±1 diet.

A 10‐month feeding trial was performed with channel catfish, Ictalurus punctatus, to re‐evaluate the minimum level of dietary vitamin E supplementation required under conditions of commercial production. Four levels (0, 15, 30 and 60 mg kg−1 diet) of supplemental vitamin E were added as DL‐α‐tocopherol acetate to a typical commercial catfish diet. Sixteen 0.04‐ha ponds were stocked in July, at a rate of 25 000 fish ha−1, with two size classes (averaging 18 and 265 g fish−1) of fingerling channel catfish, and each diet was fed to fish in four replicate ponds once daily to satiation. After 10 months of feeding, a total harvest was performed to obtain final production data, and samples were obtained from fish in all ponds. Liver and plasma samples were obtained for α‐tocopherol determination, and liver, heart and muscle samples were processed for histological evaluation. No discernible differences occurred among fish fed the different diets with respect to weight gain or survival. Mean production rate was 9734 kg ha−1, with a final average fish weight of 0.53 kg. A significant (P < 0.05) effect of diet was noted in plasma and liver α‐tocopherol levels, which increased with dietary supplementation. An effect of size also was apparent, with plasma and liver α‐tocopherol levels being higher in larger fish compared with smaller fish within a dietary treatment. Histological evaluation revealed no differences among fish fed the different dietary treatments. Based on the lack of overt histological signs of deficiency, it appears that the current level of vitamin E supplementation of commercial catfish diets may be reduced considerably with no detriment to channel catfish health or production.