Evaluating the toxicological effects of water-borne iron on hematological and oxidative stress biomarkers in Osteobrama belangeri (Valenciennes, 1844) fingerling

Iron is essential for fish, but elevated water-borne iron can cause toxicity and impair aquaculture productivity. This study evaluated the acute and sub-lethal effects of FeSO4·7H2O on Osteobrama belangeri fingerlings. The 96 h LC50 was estimated at 45.30 ± 0.99 mg L−1. Based on this value, we exposed fish to 1/16th (T1), 1/8th (T2), and 1/4th (T3) of the LC50, along with a control, for 96 h. Blood, serum, and tissue samples were collected at 24, 48, 72, and 96 h to assess hematological, biochemical, and oxidative stress responses. Iron exposure significantly (p < 0.05) increased hemoglobin concentration, hematocrit, erythrocyte and leukocyte counts, and levels of glucose, and lipid peroxidation, while significantly decreasing total protein, albumin, globulin, albumin–globulin ratio, as well as superoxide dismutase, and catalase activities. These alterations indicate physiological stress and oxidative damage in the liver, gill, and kidney. The integrated biomarker response further confirmed oxidative parameters as sensitive indicators of iron toxicity. These findings provide insights into iron tolerance in O. belangeri and support improved iron management in aquaculture. Further chronic and field studies are warranted to establish safe environmental limits.