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 le vels of iron from iron methionine (0, 30 and 300 mg/kg) were each fed to ju venile channel catfish in triplicate aquaria twice daily to apparent satiat ion for 14 weeks. Fish fed with iron-deficient diets had decreased weight g ain, feed conversion and survival. Supplementation of ascorbic acid to the iron-deficient diets further decreased weight gain and survival. Feed conve rsion was not significantly affected by dietary level of vitamin C or iron and vitamin C interaction. No gross signs of vitamin C deficiency were obse rved. Total cell count (TCC), red blood cell count (RBC), hematocrit (HCT) and hemoglobin (Hb) were significantly lower for fish fed the iron deficien t diet. TCC and RBC significantly increased when 3000 mg of vitamin C/kg wa s added. However, in the absence of dietary iron, supplementation of ascorb ic acid resulted in significant decrease in HCT and Hb values. Hepatic iron concentration increased with increasing dietary level of iron. Supplementa tion of high level of ascorbic acid to the diet containing 300 mg/kg of sup plemental iron significantly increased the liver iron content. Liver ascorb ate increased with increasing dietary level of ascorbic acid. Dietary level of iron and the interaction between iron and vitamin C had no effect on li ver content of vitamin C. Mean macrophage migration in the absence or prese nce of Edwardsiella ictaluri exoantigen was significantly higher for fish f ed the iron supplemented diets. The significant effect of vitamin C was obt ained only when high level (3000 mg/kg) was used. Neither dietary levels of iron nor vitamin C or their interaction influenced survival of juvenile ch annel catfish against E. ictaluri 14-day post challenge. However. the onset of mortality was earlier for fish fed the iron-deficient diet. (C) 2000 Pu blished by Elsevier Science B.V.