Effects of polystyrene nanoplastics on oxidative stress, histopathology and intestinal microbiota in largemouth bass (Micropterus salmoides)

Nanoplastics (NPs) can be taken up by aquatic organism and profoundly impact the growth and fitness of aquatic animals in the ecosystem. Currently, the influence of NPs in commercial fish is still poorly documented, especially in carnivorous freshwater fish. To investigate the effects of NPs in water on growth performance, oxidative stress, histopathology, and intestinal microbiota of Micropterus salmoides, juvenile fish (initial weight 14.56 ± 0.09 g) were exposed to 10 and 100 μg/L polystyrene NPs (100 nm) for seven days and nineteen days. The results showed that no significant difference was found in growth among all the experimental groups. NPs caused obvious histological changes in gills (e.g., hyperplasia, curvature, fragmentation, capillary dilatation), livers (e.g., hypertrophy, infiltration, lipid droplet, vacuolization) and intestines (e.g., increase/decrease of gut villus density and length, decrease of goblet cells). The SOD and CAT activities in livers of the high NPs (100 μg/L) group were significantly higher than that of the control group after nineteen-day exposure (P < 0.05). The MDA level of the high NPs (100 μg/L) group was significantly higher than that of the control group after seven-day exposure (P < 0.05), but no significant difference was found in MDA among all the experimental groups after nineteen-day exposure. M. salmoides might adapt to the environment containing NPs through the changes in the intestine microbiota affecting or promoting the growth of the different bacterial genera. This study provides novel insight beyond the current understanding of the potential toxicological effects and NP contamination in M. salmoides.