Re-evaluation of vitamin E supplementation of practical diets for channel catfish, Ictalurus punctatus, production
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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--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 -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 -tocopherol levels, which increased with dietary supplementation. An effect of size also was apparent, with plasma and liver -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. 1998 Blackwell Science Ltd.
