Gill Damage Patterns in Heteropneustes fossilis Exposed to Cypermethrin: A Diagnostic Tool for Monitoring Freshwater Contamination

Abstract

The widespread application of cypermethrin in agriculture leads to its persistent entry into natural waters, where it may compromise fish health. This work investigates the progression of structural disturbances in the gills of Heteropneustes fossilis exposed to sublethal cypermethrin concentrations for 24, 48, 72, and 96 hours. Gill samples were processed using standard histological techniques and examined to determine lesion patterns associated with exposure duration. Even the shortest exposure interval produced visible epithelial disruption, including swelling, local detachment, and initial fusion of secondary lamellae. As exposure time increased, lamellar deformation intensified, accompanied by hyperplasia of chloride cells, marked vacuolation, hemorrhagic regions, and distortion of pillar cell arrangement. After 96 hours of exposure, the gill framework showed severe necrosis and extensive fragmentation, suggesting functional collapse. The gradual escalation of tissue injury indicates that gill morphology can provide a sensitive measure of pesticide stress in aquatic organisms. These results confirm that cypermethrin impairs respiratory surfaces in H. fossilis and support the application of gill histopathology in monitoring chemical contamination in freshwater systems.