This study investigated histopathological alterations in the gills of juvenile common carp (Cyprinus carpio) following acute exposure to the neonicotinoid insecticide thiamethoxam in its commercial formulation (Actara). Fish were exposed to two median lethal concentrations (LC₅₀ for 24 h and LC₅₀ for 96 h), after which gill tissues were subjected to histological analysis. After 24 h of exposure (LC₅₀ 24 h – 100 mg/L), gill lesions included lifting of the respiratory epithelium, pronounced interlamellar epithelial hyperplasia, telangiectasia, and curvature of the secondary lamellae. After 96 h (LC₅₀ 96 h – 60 mg/L), these alterations were accompanied by edema of the secondary lamellae (hydropic degeneration) and dilation of blood vessels at their bases. The observed histopathological changes comprised both adaptive–protective responses (epithelial hyperplasia, epithelial lifting, and edema) and destructive–circulatory effects (telangiectasia and vascular dilation). These findings demonstrate the complex toxic effects of thiamethoxam on fish gills, reflecting the coexistence of compensatory mechanisms and irreversible tissue damage under acute exposure conditions.
Yusifova et al. (2025) studied this question.