Toxicological effects of chemical pesticides in fish: Focusing on intestinal injury and gut microbial dysbiosis.

The gut is susceptible to environmental pollutants and is a crucial barrier to exchanging internal and exterior substances in animals and humans. Intestinal microbiota plays vital roles in nutrition metabolism, synthesis of functional compounds, immune regulation, inflammation, and infection. Gut microbiota dysbiosis can induce intestinal physical barrier damage, trigger inflammation, and increase gut permeability. Intestinal barrier dysfunction facilitates the entry of pathogenic bacteria and harmful chemicals into the body through the blood circulation system, potentially causing neurotoxicity, hepatotoxicity, respiratory toxicity, growth inhibition, and even death. Herein, we overviewed the knowledge on the toxic effects of chemical pesticides on fish intestines and gut microbiota in the latest decade (2015-2025) and attempted to summarize the potential toxicological mechanisms. Chemical pesticide exposure can cause intestinal damage, impair immune function, and disrupt gut microbiota in fish. Gut microbial dysbiosis was strongly associated with intestinal injury. Alterations in gut microbiome metabolites, such as lipopolysaccharide, peptidoglycan, and short-chain fatty acids, have been linked to intestinal damage, inflammation, and changes in permeability. The mechanisms underlying intestinal injury in fish exposed to chemical pesticides included apoptosis, oxidative stress, and inflammation, which are mediated by reactive oxygen species pathways as well as death receptor and mitochondrial signaling pathways. Furthermore, pesticide-induced intestinal dysbiosis can cause neurotoxicity and hepatotoxicity through the microbiome-gut-brain/liver axis.