An experiment was conducted to compare the effects of iron oxide nanoparticles (T 1 ) and ferrous sulfate (T 2 ) on Indian major carp, Labeo rohita H. There were significant differences (P \ 0.05) in the final weight of T 1 and T 2 compared with the control. Survival rates were not affected by the dietary treatments. Fish fed a basal diet (control) showed lower (P \ 0.05) iron content in muscle compared to T 1 and T 2 . Furthermore, the highest value (P \ 0.05) of iron content was observed in T 1 . In addition, RBCs and hemoglobin levels were significantly higher in T 1 as compared to other treated groups. Different innate immune parameters such as respiratory burst activity, bactericidal activity and myeloperoxidase activity were higher in nano-Fe-treated diet (T 1 ) as compared to other iron source (T 2 ) and control in 30 days post-feeding. Moreover, nano-Fe appeared to be more effective (P \ 0.05) than ferrous sulfate in increasing muscle iron and hemoglobin contents. Dietary administration of nanoFe did not cause any oxidative damage, but improved antioxidant enzymatic activities (SOD and GSH level) irrespective of different iron sources in the basal diet.