Effects of dietary iron sources on muscle development, nutrient composition, antioxidant status, and iron metabolism in yellow catfish (Pelteobagrus fulvidraco)

Iron is an essential micronutrient in aquafeeds, yet the biological impacts of its chemical forms on fish physiology remain insufficiently characterized. This study investigated the effects of different dietary iron sources on muscle development, proximate composition, antioxidant status, and iron metabolism in yellow catfish Pelteobagrus fulvidraco, providing scientific evidence for optimizing iron supplementation in aquafeeds. Juvenile specimens were assigned to five experimental diets: FeSO₄, Fe-Gly, FeCl₂, Fe-CA, and Fe₂O₃ NPs during a 10-week feeding trial. The results revealed that none of the iron sources significantly affected muscle moisture or ash content. However, the Fe-Gly and Fe-CA exhibited significantly lower crude lipid content, while Fe₂O₃ NPs reduced crude protein content. Compared to the FeSO₄, Fe₂O₃ NPs significantly reduced antioxidant enzyme activities and the GSH/GSSG ratio, accompanied by elevated malondialdehyde (MDA) levels. This group also showed downregulation of mRNA expression of antioxidant-related genes. Conversely, Fe-Gly demonstrated superior antioxidant capacity by enhancing enzymatic activities and gene expression patterns. Additionally, FeCl₂ and Fe-CA exerted varying degrees of influence on the muscle antioxidant status. Histological analysis demonstrated that muscle fibers in the Fe-Gly and Fe-CA groups were densely arranged and exhibited superior morphology, whereas those in the Fe₂O₃ NPs group were loosely arranged. Gene expression analysis further showed that the Fe-Gly and Fe-CA groups significantly upregulated the mRNA expression of myf5, mrf4, and mef2d genes, while suppressing the mRNA expression of pax7 and mstn genes. Conversely, the Fe₂O₃ NPs group appeared to exacerbate muscle development inhibition by significantly downregulating myod and myog mRNA expression and upregulating mstn mRNA expression. Iron metabolism analysis indicated Fe-Gly enhanced muscle iron deposition and upregulated mRNA expression of iron transport genes (dmt1, fpn1, ftl, irp1, tf, and tfr1), whereas Fe₂O₃ NPs increased fth mRNA expression while reducing tf and tfr1 transcript levels. In conclusion, Fe-Gly exhibits considerable application potential due to its superior antioxidant properties, promotion of muscle development, and efficient iron utilization. However, the observed adverse effects of Fe₂O₃ NPs warrant further investigation into nanoparticle safety in aquatic species. This study provides valuable insights for selecting appropriate iron sources in aquafeed formulations.