Potential Risk Assessment of Different Sizes of Microplastics on the Digestive System of Hybrid Sturgeon

Microplastics are pollutants that are widely present in aquatic environments. Currently, research on the effects of microplastics of different particle sizes on freshwater fish remains relatively limited. This study utilized polyethylene microplastic particles of 1 µm and 5 µm to expose hybrid sturgeon( Acipenser baerii ♂×A. schrenckii ♀ ), analyzing changes in intestinal ultrastructure, digestive enzyme activity, and gut microbial composition (based on high-throughput sequencing of the 16S rRNA V3–V4 region). The results indicate that microplastics of both particle sizes cause changes in intestinal ultrastructure and digestive enzyme activity. The alpha and beta diversity of gut microbiota in the exposed groups were significantly higher than those in the control group. At the phylum level, the relative abundances of Bacteroidetes, Actinobacteria, and Desulfobacterota significantly increased (P < 0.01); at the genus level, the abundances of Pseudomonas , Lactobacillus , Enterobacter , Desulfovibrio, HIMB11 , and Muribaculaceae also significantly increased (P < 0.01). Furthermore, functional predictions of the microbiota indicated that the abundance of functions related to diseases, cellular processes, and organism systems increased in the 5 µm treatment group, while the abundance of functions related to genetic information processing significantly decreased (P < 0.05, FDR < 0.05). This study reveals the potential risks of microplastics to the digestive physiology and intestinal digestive system of sturgeon, providing a basis for further exploration of the mechanisms by which different particle sizes of microplastics affect freshwater fish.