Effect of thiamethoxam on the behavioral profile alteration and toxicity of adult zebrafish at environmentally relevant concentrations.

Thiamethoxam (THM) is a commercial neonicotinoid insecticide with broad-spectrum insecticidal activity. It has been widely detected in the aquatic environment, but its behavioral toxicity on aquatic organisms received limited attention. In this study, adult zebrafish were exposed to THM at three levels (0.1, 10, and 1000 μg/L) for 45 days to investigate its effect on their ecological behavior, histopathology, bioaccumulation, and stress response. The bioconcentration factor in zebrafish brain was significantly higher (p < 0.05) at low concentration of THM (0.1 μg/L) than in other treatment groups. In terms of individual behavior, the locomotor activity, aggregation, and social activity of fish were enhanced after THM exposure, but the memory of the food zone was disturbed and abnormal swimming behavior was observed. THM exposure caused brain tissue necrosis, erythrocyte infiltration, cloudy swelling, and other pathological changes in brain tissue and affected the concentrations of acetylcholinesterase and cortisol related to neurotoxicity. The condition factor and organ coefficients (brain, heart, and intestine) of zebrafish were markedly impacted by THM treatment at 0.1 and 1000 μg/L, respectively. This finding showed that THM was more harmful to fish behavior than lethality, reproduction, and growth, and a behavioral study can be a useful tool for ecological risk assessment.