The effects of the addition of iron sulfateheptahydrate to rainbow trout (Oncorhyncus mykiss) feedrations on growth, antioxidant enzymes, and thermalstress

In this study, the effects of different doses of iron addition to plant-based feed formulation on growth performance, feed intake, nutritional composition, digestibility, iron-related serum parameters, and gene expression in juvenile rainbow trout (Oncorhynchus mykiss) were evaluated. Additionally, fish were exposed to thermal stress, and the effects of feeding and thermal stress on the expression of antioxidant enzymes and some immunity-related genes were examined. The fish were fed with no iron supplementation (Fe0), 150, 300, and 600 mg of iron/kg feed iron supplementated (Fe150; Fe300; Fe600) and commercial feed (CMF) for 60 days. Then, the fish were exposed to thermal stress by increasing the water temperature by 1 ºC per day, from 17 ºC to 24 ºC in 7 days. At the end of the feeding trial, the growth performance of the fish was best in the Fe150, Fe300 and CMF groups; Digestibility coefficients (%ADC) were found to be over 90% in the Fe150 and Fe300 groups. The highest CAT activity was obtained in the Fe150, Fe300 and CMF groups, and the highest SOD level was obtained in the Fe150 group. Considering HSP70, Cas3 and IL1 mRNA gene expressions, iron doses in the Fe300 and Fe600 groups caused stress for fish. Compared to the feeding final, TBARS activities of all groups except Fe0 decreased with thermal stress. SOD activities after thermal stress did not differ among the experimental groups. The highest CAT activity was observed in the Fe150 group and showed similar results with the Fe300 and CMF groups. At the end of thermal stress, HSP70 mRNA expression decreased and HSP90 mRNA expression increased in the Fe150 and CMF groups, which were considered the optimum dose. The highest CAT activity was observed in the Fe150 group and showed similar results with the Fe300 and CMF groups. After thermal stress, HSP70 mRNA expression decreased and HSP90 mRNA expression increased in the Fe150 and CMF groups, which were considered the optimum doses. The higher levels of HSP90, Cas3, and IL1 mRNA showed that fish in the Fe150 and CMF groups were able to respond well to heat stress.