RESUMO
Two 12-wk experiments were conducted to determine the adequate dietary niacin levels for juvenile hybrid tilapia, Oreochromis niloticus x O. aureus, when diets containing either 38% D(+)-glucose or 38% dextrin (type III, from corn) as the carbohydrate source were fed. In Experiment 1, we used 0, 40, 80, 120, 160 and 200 mg/kg of supplemental niacin in both the glucose- and dextrin-containing diets. In Experiment 2, 0, 10, 25, 40 and 55 mg/kg or 0, 10, 25, 40, 80, 120 and 160 mg/kg of supplemental niacin was incorporated in diets containing glucose or dextrin, respectively. In both experiments, fish fed niacin-deficient diets grew poorly. They developed skin, fin and mouth lesions and hemorrhages; the snout was deformed and there was gill edema. These pathologies began 6 wk after the experiments started. Plasma glucose concentrations were higher in fish fed glucose diets than those fed dextrin diets. Weight gain analyzed by broken-line regression indicated that the adequate dietary niacin level for maximal growth in rapidly growing tilapia fingerlings is 26 mg/kg in fish fed the glucose diet and 121 mg/kg in fish fed the dextrin diet.
