Interaction between dietary levels of iron and vitamin C on growth, hematology, immune response and resistance of channel catfish (Ictalurus punctatus) to Edwardsiella ictaluri challenge

Nine egg-white-based diets supplemented with three levels of vitamin C from L-ascorbyl-2-polyphosphate (0, 50 and 3000 mg/kg) for each of the three levels of iron from iron methionine (0, 30 and 300 mg/kg) were each fed to juvenile channel catfish in triplicate aquaria twice daily to apparent satiation for 14 weeks. Fish fed with iron-deficient diets had decreased weight gain, feed conversion and survival. Supplementation of ascorbic acid to the iron-deficient diets further decreased weight gain and survival. Feed conversion was not significantly affected by dietary level of vitamin C or iron and vitamin C interaction. No gross signs of vitamin C deficiency were observed. Total cell count (TCC), red blood cell count (RBC), hematocrit (HCT) and hemoglobin (Hb) were significantly lower for fish fed the iron deficient diet. TCC and RBC significantly increased when 3000 mg of vitamin C/kg was added. However, in the absence of dietary iron, supplementation of ascorbic acid resulted in significant decrease in HCT and Hb values. Hepatic iron concentration increased with increasing dietary level of iron. Supplementation of high level of ascorbic acid to the diet containing 300 mg/kg of supplemental iron significantly increased the liver iron content. Liver ascorbate increased with increasing dietary level of ascorbic acid. Dietary level of iron and the interaction between iron and vitamin C had no effect on liver content of vitamin C. Mean macrophage migration in the absence or presence of Edwardsiella ictaluri exoantigen was significantly higher for fish fed the iron supplemented diets. The significant effect of vitamin C was obtained only when high level (3000 mg/kg) was used. Neither dietary levels of iron nor vitamin C or their interaction influenced survival of juvenile channel catfish against E. ictaluri 14-day post challenge. However. the onset of mortality was earlier for fish fed the iron-deficient diet. (C) 2000 Published by Elsevier Science B.V.