Technical Abstract: Juvenile channel catfish were fed egg-white based diets with or without 20 mg supplemental iron/kg from iron methionine for 13 weeks. Subsequently, fish from each treatment were divided into two groups and were fed with either the iron-deficient or replete diets for another 4 weeks. At the end of week 13, fish fed the iron-deficient diet had significantly lower weight gain, feed efficiency ratio, hematocrit, total cell count, and serum iron and transferrin saturation than those fed the replete diet. These values remained consistently low or decreased for the groups which continued to receive or were switched to the iron-deficient diet, but were improved for those fed the replete diet. The differences, however, were not always significant. Chemotactic response of peritoneal macrophages to Edwardsiella ictaluri exoantigen was suppressed for fish fed the iron-deficient diet, but the abnormality was reversed by feeding the iron-replete diet. However, the challenge study showed that dietary iron did not protect channel catfish against mortality from E. Ictaluri, but the onset of mortality was earlier for fish fed the iron-deficient diet due probably to the combined effect of iron deficiency and infection.