Dietary iron fortification did not affect the intestinal microbiome for channel catfish (Ictalurus punctatus) juveniles, but decreased their resistance against Edwardsiella ictaluri

Authors: YAMAMOTO, FERNANDO - Mississippi State University; Older, Caitlin; KHOO, LESTER - Mississippi State University; ROMANO, NICHOLAS - Virginia State University; Richardson, Bradley; Ott, Brian; WISE, DAVID - Mississippi State University; WARE, CYNTHIA - Mississippi State University; GOODMAN, PENELOPE - Mississippi State University; REIFERS, JONATHAN - Mississippi State University; GRIFFIN, MATT - Mississippi State University

Submitted to: Journal of Fish Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2024
Publication Date: 12/10/2024
Citation: Yamamoto, F.Y., Older, C.E., Khoo, L.H., Romano, N., Richardson, B.M., Ott, B.D., Wise, D.J., Ware, C., Goodman, P.M., Reifers, J.G., Griffin, M.J. 2024. Dietary iron fortification did not affect the intestinal microbiome for channel catfish (Ictalurus punctatus) juveniles, but decreased their resistance against Edwardsiella ictaluri. Journal of Fish Diseases. Article 14060. https://doi.org/10.1111/jfd.14060.
DOI: https://doi.org/10.1111/jfd.14060

Interpretive Summary: Idiopathic catfish anemia (ICA) has been an ongoing issue affecting the United States catfish industry for decades. While catfish anemia has been linked to nutrition, recent farm cases appear to rule out feed-related anemia, as outbreaks tend to occur in isolated ponds, while other ponds receiving the same feed show no signs of disease. To mitigate this issue, catfish feed mills have supplemented their diets with levels of iron sulphate which exceed the normal amount by at least 5.5-fold. It is currently unknown what effects this may have on fish health, particularly with respect to intestinal pathogens, which can also utilize iron. Mississippi State University researchers in collaboration with scientists from Virginia State University and the USDA ARS Warmwater Aquaculture Research Unit in Stoneville, MS, conducted a research study to better understand the effects of excess dietary iron sulphate on channel catfish health. Channel catfish (Ictalurus punctatus) were fed diets containing either no added iron sulphate or 1000 mg/kg iron sulphate for nine weeks. Production performance, intestinal microbiota, and susceptibility to infection by bacterial catfish pathogen Edwardsiella ictaluri were evaluated. No differences in production performance were identified, however bacterial communities present in the gut were affected and reduced survival was observed for fish fed iron-supplemented diets. These results may suggest that excess iron sulphate supplementation in diets can make fish more susceptible to E. ictaluri infection. Iron should be supplemented carefully in catfish diets, preferably only during periods when ICA is most likely to occur.

Technical Abstract: Idiopathic catfish anemia (ICA) has been an ongoing issue affecting the United States catfish industry for decades. This disease typically manifests in early spring or late fall; however, due to its sporadic nature and occurrence, its etiology has remained elusive. While catfish anemia has been linked to nutrition, parasite infestation, and waterborne toxins, recent farm cases appear to rule out feed-related anemia, as outbreaks tend to occur in isolated ponds, while other ponds receiving the same feed show no signs of disease. To mitigate this issue, catfish feed mills have supplemented their diets with iron sulphate to improve erythropoiesis and, in turn, prevent the onset of anemia. Despite no empirical evidence was presented to support this iron supplementation, a linear increase in blood hematocrit was later observed for hybrid catfish (Ictalurus punctatus × I. furcatus) fed graded levels of iron sulphate. Nevertheless, a numerical reduction in survival was also observed for fish fed iron supplemented diets when challenged with the causative bacteria of enteric septicemia of catfish (Edwardsiella ictaluri). Iron is an essential micronutrient for teleost fish, and supplementation of this element in the mineral premix is a standard practice in aquafeeds. The mineral requirements for farmed aquatic species typically ranges from ~60-170 mg/kg. However, the catfish industry has consistently included 700-1000 mg/kg, surpassing the normal range by at least 5.5-fold. This practice raises concern, as vertebrates use physiological mechanisms to sequester iron from circulation during bacterial infections, thereby depriving invading microorganisms of this essential nutrient. It is thought that excess dietary iron may compromise this host defense strategy, particularly against enteric pathogens. The present study evaluated dietary supplementation of iron sulphate at either 0 or 1000 mg/kg to better understand the implications of iron supplementation on production performance, the intestinal microbiome in channel catfish (Ictalurus punctatus) and subsequent susceptibility to E. ictaluri infection.