Supplementation of iron sulfate in plant-based feeds has been a common practice to mitigate idiopathic catfish anemia. Two separate feeding trials evaluated the supplementation of iron in feeds for hybrid catfish (Ictalurus punctatus × I. furcatus) and channel catfish (I. punctatus). For the first feeding trial, four experimental diets were formulated with practical ingredients and supplemented with ferrous monosulfate to provide 0, 500, 1000, and 1500 mg of iron per kg of diet. Groups of 16 hybrid catfish juveniles (~22.4 g) were stocked in each of 20, 110-L aquaria (n=5), and experimental diets were distributed in a completely randomized block design. Fish were fed to apparent satiation for 12 weeks, and at the end of the study, production performance, survival, condition indices, and protein and iron retention were unaffected by the dietary treatments. Hematocrit levels as well as the iron concentration in the whole-body presented a linear increase as the concentration of iron increased in the diets. The remaining fish from the feeding trial were challenged with a virulent strain of Edwardsiella ictaluri through immersion at 1.2×107 CFU/mL for 1 h. The mortality rate was not significantly different but appeared to be higher for the dietary groups treated with iron-supplemented diets. Intestinal histology samples are being processed, and results are pending.
A follow-up trial conducted with channel catfish evaluated the supplementation of 1000 mg/kg, and a basal diet served as a control. The iron supplementation level was chosen based on the previous study, and what has been practiced by the catfish feed industry. Groups of 30 channel catfish juveniles (~13.3 g) were distributed in each of 16, 110-L aquaria (n=8), and experimental diets were distributed in a completely randomized block design. After 90 days of feeding, production performance, survival, condition indices, total cell count in the blood, plasma protein, and whole-body proximate composition were unaffected by the dietary treatments. Blood hematocrit increased when fish were fed 1000 mg/kg of iron. The transient microbiome did not present differences for the alpha and beta diversity metrics, nor for testing of differentially abundant bacterial taxa. The remaining fish were exposed to a bath exposure of E. ictaluri (3.2×108 CFU/mL) for 1 h, and fish fed the iron-supplemented diet had a significantly lower survival (27%) when compared to the control group (43%). These two trials indicate that iron supplementation above their established requirement level can increase their hematocrit levels, but also increase susceptibility to E. ictaluri.