Nanoplastics in aquatic ecosystems: Disruptions to fish digestive physiology and gut microbiota.

Nanoplastics (NPs) have emerged as pervasive contaminants in aquatic ecosystems, raising concerns due to their small size, high reactivity, and bioaccumulation potential. This review examines their impacts on fish digestive physiology and gut microbiota, highlighting key mechanisms and ecological implications. Evidence shows that NPs disrupt intestinal integrity by causing epithelial damage, villus degeneration, and increased gut permeability. These changes impair digestive enzyme activity, reducing nutrient absorption and growth performance. NPs also induce oxidative stress through excessive reactive oxygen species (ROS) production, weakening antioxidant defenses and triggering inflammation in digestive tissues. Additionally, NPs alter gut microbial communities by reducing diversity, depleting beneficial taxa, and promoting opportunistic pathogens. This dysbiosis affects metabolic functions, immune responses, and overall fish health. Co-exposure with other contaminants may further intensify these effects. Emerging studies suggest that dietary strategies, such as probiotics and prebiotics, could help mitigate NP-induced damage and restore gut balance. Despite recent progress, significant knowledge gaps remain regarding long-term exposure, species-specific responses, and molecular toxicity mechanisms. Future multidisciplinary research is essential to improve risk assessment and develop sustainable mitigation strategies for aquaculture and aquatic ecosystems.