Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 28, 1997
Publication Date: N/A
Interpretive Summary: Losses of cultured fish from enteric septicemia of catfish (ESC) caused by a bacterium Edwardsiella ictaluri cost the farmers about $50 million annually. Attempts to prevent and control this disease by various means have met with little success. It has been shown that, in man and land-animals deficiencies of nutrients adversely affect the host defense against diseases. For channel catfish, available information on relationship between nutrition, immunity and disease resistance is very limited. Thus, this study was conducted to find out if the immune response and resistance of catfish to the bacterium E. ictaluri are affected by dietary iron. Growth response and blood parameters were also evaluated. Results showed that fish fed diet without iron had poor growth,survival, and feed efficiency and developed characteristic signs of anemia. Deficiency of iron also decreased the activity of white blood cells (macrophages) in response to the bacterial products, but this abnormality can be reversed by feeding iron-adequate diet for 4 weeks. Dietary iron, however, did not protect fish from ESC but the on-set of mortality was delayed for fish fed the iron-adequate diet. This information is essential to feed formulator for improving feed quality and serves a base-line data for future research on nutrition, immunity, and disease resistance.
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.