Evaluation of Morphological and Behavioral Alterations in Clarias Batrachus following Acute Zinc Exposure

Heavy metal contamination poses a significant threat to freshwater ecosystems. Zinc an essential trace element, exhibits toxicity at elevated concentrations, adversely affecting physiological, morphological, and behavioral responses in aquatic organisms. The present study aimed to investigate the dose-dependent morphological and behavioral alterations in freshwater fish Clarias batrachus during a 96-hour acute toxicity exposure to zinc sulphate (ZnSO4·7H2O). Fish were exposed to graded concentrations ranging from 50 to 250 mg/L under static renewal conditions. Morphological changes observed included excessive mucus secretion, skin discoloration, fin erosion, and gill necrosis, which intensified with increasing concentrations. Behavioral anomalies such as hyperactivity, erratic swimming, surface respiration, spiralling, and loss of equilibrium emerged as early indicators of sublethal stress. The severity of both morphological and behavioral responses showed a direct correlation with zinc concentration and exposure duration. These changes suggest systemic physiological disturbances, including respiratory and neurological dysfunction. The study demonstrates that both morphological and behavioral parameters serve as reliable biomarkers of zinc toxicity, offering valuable insights into the health status of aquatic organisms under environmental stress. The findings contribute to environmental toxicology by supporting the use of C. batrachus as a sentinel species for monitoring heavy metal contamination and establishing safe ecological thresholds.