Abstract
Catfish (Ictalurus punctatus) and rainbow trout (Oncorhynchus mykiss) are the leading fish food in the United States. Iron (Fe) is an essential element for fish; however, a higher dose could exert toxic effects on fish. Vitamin C is a reducing agent that helps in facilitating iron uptake in the gut. Bentonite clay acts as a chelating agent. Our study investigated the effect of dietary supplementation of vitamin C and bentonite in mitigating the iron toxicity in catfish and trout. Vitamin C study: Catfish were exposed with/without iron (9.5 mg/L Fe3+ in water) and fed 3 diets [control, low vitamin-C (143 ppm), and high vitamin-C (573 ppm)] for 8 weeks. Results showed that fish growth was lower in iron exposed compared to non-exposed groups. Supplementations of vitamin C increased the growth rate, reduced oxidative stress, and mitigate the organs damages under iron-exposed conditions. Bentonite study: Six diets [0% bentonite (Con), 2% bentonite (LB), 4% bentonite (HB), 0.25% iron as FeSO4 (Fe), Fe+2% bentonite (LBFe), and Fe+4% bentonite (HBFe) were fed to trout for 8 weeks. Significantly lower fish growth was observed when fed Fe compared to control, however bentonite supplementation improved the growth. Oxidative status was enhanced in LBFe and HBFe groups compared to the Fe group. The liver showed infiltration with inflammatory cells and necrosis in Fe and HB groups whereas the LBFe group appears to be normal. Bentonite and Vitamin C study: Seven diets [500 ppm vitamin-C (Con), 0.25% iron as FeSO4 (Fe)+ Vitamin-C(500ppm) (ConFe), 2% bentonite, 0.25% iron as FeSO4 (Fe) (BenFe), Fe+1500 ppm Vitamin-C (MVCFe), Fe+2% bentonite + 1500 ppm Vitamin-C (MVCBenFe), Fe+3000 ppm Vitamin-C (HVCFe), and Fe+2% bentonite + 3000 ppm Vitamin-C (HVCBenFe) were fed to trout for 10 weeks. The result indicated that the supplementation of bentonite, vitamin C ,or in combination exposed to a higher dietary iron augmented (p < 0.05) their growth performance compared to the ConFe group. The liver and gills showed a series of histological changes in ConFe, which was accompanied by a significant rise in hepatic and muscle iron overload. The supplementation of bentonite, vitamin C, or in combination reduced the augmented concentrations of iron accumulation to that of ConFe group. Also, the MDA level was significantly higher in ConFe groups than in the rest of the groups. Similarly, the expression of the antioxidant gene was upregulated with the supplementation of bentonite, vitamin C, or in combination. Further, the gene expression of Hepcidin (HAMP, transferrin (Tf), and Hemeoxygenase (HO1) were upregulated in the ConFe group compared to the rest groups. Overall, dietary supplementation of vitamin C and bentonite can be an effective approach to mitigate the iron toxicity in the catfish and trout aquaculture industry.