Exposure to microplastics induces lower survival, oxidative stress, disordered microbiota and altered metabolism in the intestines of grass carp (Ctenopharyngodon idella)

There are major gaps in illustrating the risk to freshwater fish that are exposed to environmental microplastics (MPs), even though MPs in freshwater environments has drawn much concern. To explore the potentially negative effects of microplastics on freshwater fish, grass carp (averaging 9.215 ± 0.035g) were exposed to microplastics (32–40 μm in diameter) at two environmental concentrations (100 and 1000 μg/L) for 21 days, and evaluated for physio-biochemical performance, gut microbiome, and metabolome responses. After exposure, microplastics were detected in the intestine and within basal nuclei and goblet cells hyperplasia. Antioxidant enzyme activities (superoxide dismutase and catalase) also significantly decreased within the intestines (P < 0.05). Through 16S rRNA gene sequencing analysis, a decrease in diversity and richness was observed in the MPs-H and MPs-L groups. The abundance of opportunistic pathogens increased and beneficial bacteria decreased in both MP treatments. For example, Acinetobacter and Bosea proportions were higher in the MPs-L group, while Bacteroides and Shewanella increased in the MPs-H group. Furthermore, abundance of Lactobacillus decreased both in the MPs-H and MPs-L groups. Metabolomics analysis revealed primary bile acid biosynthesis metabolism upregulated in the MPs-L and purine metabolism downregulated in the MPs-H group. Additionally, an integration analysis of the gut microbiome and metabolomics identified significant associations between several bacteria taxa and metabolites related to intestinal repair. Taken together, these results highlighted the negative effects on intestinal morphology, oxidative stress, and microbiome and emphasized the relationship between microbiota and metabolites in response to microplastics, which could provide comprehensive insights into the potential risks of MPs on freshwater fish intestines.