Comparative toxicity of thiamethoxam and abamectin in red swamp crayfish: Bioaccumulation, oxidative stress, and gut microbiota in a rice-crayfish Co-culture system.

The expansion of integrated agriculture-aquaculture systems, while economically beneficial, introduces complex environmental challenges, particularly concerning pesticide runoff and its impact on non-target aquatic species. The rice-crayfish co-culture system, a prevalent agricultural model in China, exemplifies this dichotomy, where crop protection practices may inadvertently compromise the health of co-cultured organisms. Here this study investigate the ecotoxicological effects of two widely used pesticides-thiamethoxam (TMX), a neonicotinoid insecticide, and abamectin (ABM), a macrocyclic lactone-on the red swamp crayfish (Procambarus clarkii), a co-culture species in this integrated system. Through a 14-day controlled exposure experiment (0, 0.1, 1, and 10 μg/L), this study comprehensively assessed organismal, biochemical, transcriptional, and microbial responses. Our results demonstrate marked differential toxicity between the two compounds. TMX exhibited substantially greater bioaccumulation potential and acute toxicity, manifested as TMX caused significantly higher mortality than ABM. Multi-parametric analysis revealed that both pesticides induced hepatopancreatic injury, evidenced by elevated aspartate aminotransferase (AST) activity, and disrupted lipid metabolism, manifested as altered triglyceride (TG) and cholesterol (CHO) homeostasis. Oxidative stress emerged as a central mechanism, with malondialdehyde (MDA) accumulation and dysregulated antioxidant enzyme activities (SOD, CAT, GPx, GSH) indicating progressive failure of cellular defense systems. Transcriptional profiling further elucidated these mechanisms: while ABM elicited a classic hormetic response in heat shock protein (HSP70, HSP90, Dnaj-1, Dnaj-2) and antioxidant gene expression, TMX exposure resulted in monotonic suppression of these protective pathways, correlating with its enhanced toxicity. Notably, high-concentration pesticide exposure profoundly perturbed intestinal microbial communities, reducing taxonomic diversity and enriching opportunistic pathogens (Citrobacter, Aeromonas, Dysgonomonas), with TMX inducing more extensive dysbiosis and predicted functional disruption of 62 metabolic pathways versus four for ABM. These findings establish a mechanistic framework for pesticide toxicity in crustaceans and reveal that TMX poses a more significant ecotoxicological threat than ABM in rice-crayfish coculture systems. The results underscore the need for pesticide selection strategies that balance agricultural productivity with ecosystem health in integrated farming systems.