<p>The widespread use of antibiotics in human and veterinary medicine has led to the presence of their residues in aquatic environments, primarily due to their high-water solubility and poor bioavailability. As a result, fish, being a crucial part of the aquatic ecosystem, are continually exposed to the risk of antibiotic toxicity, which can significantly disrupt their normal physiological functions. Therefore, the aim of the study was to assess the impact of the antibiotic Norfloxacin (NOR) on the edible fish species <i>Heteropneustes fossilis</i>. Fish were treated with four different concentrations (mg/L) of NOR (0.0025, 0.1, 4 and 160) for 7 days, and different hematological and serum biochemical changes were examined. The result of the present study revealed that fish exposed to 160&#xa0;mg/l had significant changes in their blood and serum biochemical parameters relative to the control. These changes include fluctuations in RBC count, WBC count, Hb content, Ht%, and O₂ carrying capacity of blood, as well as levels of AST, ALP, ALT, and LDH. Additionally, the exposed fish exhibited variations in the levels of cholesterol, triglycerides, glucose, total protein, albumin, globulin, bilirubin, and creatinine in their serum. Nevertheless, the treatment of fish with 0.0025&#xa0;mg/l resulted in the least impact on the above-mentioned parameters. Structural changes, including membrane and nuclear disintegration along with deformation and vacuolation of cells, were also observed in the RBCs of NOR-exposed fishes. Changes in the structure and percentage of deposited and circulating immune cells in spleenic smears were also observed in NOR-exposed group. As a result, our study provides valuable insights into the potential ecotoxicity of NOR on aquatic organisms.</p>