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The quantitative dietary ascorbic acid requirements of fingerling Nile tilapia, Oreochromis niloticus L., were assessed by feeding seven diets containing graded supplements of this vitamin (0,50,75,100,125,300 and 400mg/100g dry diet) to triplicate groups of fish for 12 weeks. Fish fed the diet devoid of ascorbic acid exhibited significantly (P < 0-01) poorer growth and higher condition factor. Food conversion and protein efficiency ratios were improved with increasing dietary ascorbic acid level up to 125mg/100g of dry diet. Protein utilization, haematocrit, haemoglobin level and tissue ascorbate concentrations were depressed in fish fed the ascorbic-acid-free diet. Tissue ascorbate concentrations, especially for liver, were highly correlated with dietary ascorbic acid level. Fish fed the ascorbic-acid-free diet exhibited deficiency signs including erratic and convulsive swimming, anorexia, lethargy, caudal fin erosion, skin haemorrhages and mortality. Based on the nutritional and pathological parameters investigated, the recommended dietary inclusion level is 125mg/100g dry diet, which is equivalent to a net requirement (after processing and storage) of 42mg/100g diet.

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Abstract. Ascorbic acid depleted Oreochromis niloticus fingerlings were fed on each of three diets providing nil, normal and luxus levels of the vitamin, after small surgical incisions had been made in the dursoluteral musculature. Fish from each group were sampled regularly over 16 days and histopathological evaluation of the lesion area carried out. The tissue ascorbate levels were measured in each group during the study. The results showed that the epithelial element of the healing process developed irrespective of the vitamin level but although fibroblast activity was marked in all three groups, coltagenization was very much slower in the deficient group, and in these the lesion was not mature, even at the termination of the experiment.