Adverse effects of polystyrene microplastics in the freshwater commercial fish, grass carp (Ctenopharyngodon idella): Emphasis on physiological response and intestinal microbiome

Microplastics (MPs) pollution in aquatic environment has attracted global attention in recent years. To evaluate the potential toxic effects of MPs in freshwater cultured fish, grass carps (Ctenopharyngodon idella) (body length: 7.7 +/- 0.1 cm, wet weight: 6.28 +/- 0.23 g) were exposed to different sizes (0.5 mu m, 15 mu m) and concentrations (100 mu g/L, 500 mu g/L) of polystyrene microplastics (PS-MPs) suspension for 7 and 14 days, followed by 7 days of depuration, de-tecting the variations in growth rate, histological structure, oxidative response and intestinal microbiome. Our results indicate that MP toxicity elicited significant size-and concentration-dependent responses by grass carp. MP exposure caused obvious decrease in growth rate on day 14 but not on day 7. Additionally, MPs with large size and high concen-tration caused more severe intestinal damage and less weight gain, while MP particles with small size and high concen-tration induced more severe liver congestion and stronger oxidative stress. MP exposure dramatically shifted the gut microbial composition, with the top 10 genera in abundance being associated with the diameter and concentration of the MPs. After 7 days of depuration, only superoxide dismutase and malondialdehyde in liver, showed a tendency to recover to the initial values. Even though the differences in the gut microbial community between the control and treatment groups disappeared, and the proportion of potential pathogenic bacteria in intestine was still high. Thus, it is clear that a short-term depuration period of 7 days is not enough for complete normalization.

Automated summary

This study investigates the potential toxic effects of different sizes and concentrations of polystyrene microplastics on grass carp, and finds that the toxic effects are dependent on the size and concentration of microplastics. Exposure to microplastics leads to decreased growth rate, increased intestinal damage, and oxidative stress in the fish. Microplastics also significantly alter the composition of the fish's intestinal microbiome. Furthermore, a 7-day depuration period is not sufficient for complete normalization.