Ingestion, egestion and post-exposure effects of polystyrene microspheres on marine medaka (Oryzias melastigma)

Microplastics (MPs) are of environmental concern due to their bioavailability and potential impacts on a wide range of marine biota. In this study, we investigated the ingestion, bioaccumulation and egestion of fluorescent polystyrene (PS) micospheres (10 μm) in both larvae and adults of marine medaka (Oryzias melastigma), with or without food supply. The post-exposure effects of non-fluorescent PS (10 μm) on the survival, growth and reproduction of medaka larvae were also explored. Results showed that the PS microspheres could be ingested by both larvae and adults during the 48 h-exposure. Notably, feeding status was found to significantly affect the ingestion in medaka adults, which was not observed in the larvae. The egestion process of PS was rapid during the first recovery day but there was still certain percent of particles retained in digestive tracts at the end of 7 d recovery for either larvae or adults. After a 14 d pre-exposure with the non-fluorescent PS microspheres, the subsequent survival, growth and reproduction of medaka larvae were all significantly affected at the end of 120 d of experiment without PS. Overall, these results indicate that fishes might ingest or retain more MPs if the environmental abundance of MPs continues to increase while the available food decreases. Medaka fishes in larval stage have no capacity to select natural food sources like the adults. The chronic and "legacy effect" of MPs might also be a problem worthy paid more attention in future research instead of acute and immediate effect studies.