In recent years, several studies showed that the initial stages of fishes are able to ingest microplastics or absorb them through the gills. These plastic particles with less than 5 mm can cause gut blockage and limit food intake but also can have negative effects on growth, development, reproduction and even lead to death. Although an increasing number of studies focus on the ingestion and effects of microplastics, most studies are laboratory-based, and field studies are still very limited. Therefore, the present work aimed to evaluate if microplastics are being ingested or absorbed by wild larval stages of fishes, collected from the Douro Estuary (northern Portugal), an estuarine nursery ground for marine fish species. Monthly surveys were performed over 1 year (2021-2022) to collect fish larvae and microplastics from water samples. Samples were sorted, fish larvae identified and two fish species relevant for human consumption were chosen to evaluate their ingestion rate, namely the Senegalese sole, Solea senegalensis and the European sardine, Sardina pilchardus. A total of 30 fish larvae of S. senegalensis and 100 fish larvae of S. pilchardus were analyzed to extract microplastics, using a previously optimized protocol where the organic matter is degraded with H2O2 at 65°C. Microplastics present in the water were also quantified, and all microplastics retrieved from water and larval fish samples were characterized in terms of size, color, shape, and the polymer identified through FTIR. So far, results showed that all the microplastics present in fish larvae were fragments or fibers of 0.01 - 2.0 mm in size, and of 8 different colors. In contrast, a higher variety of shapes was observed in water samples, including fibers, fragments, films, foam, and paint, in more than 10 colors and ranging between 0.01 - 5 mm in size. These preliminary results indicate that microplastics present in fish larvae are similar to the ones from the estuarine water, although only the small size plastic fragments or fibers were ingested/absorbed by fish larvae. This study will allow to investigate microplastic occurrence in the initial stages of fishes from an estuarine nursery area, evaluating the incidence of microplastic present in fish larvae and comparing these results with the microplastics collected in the water.
Acknowledgments: This research was partially funded by Ocean3R (NORTE-01-0145-FEDER-000064) and ATLANTIDA (NORTE-01-0145-FEDER-000040) projects and FCT — Foundation for Science and Technology, Portugal within the scope of UIDB/04423/2020 and UIDP/04423/2020. Financial support from FCT was also provided through the grant awarded to S.M. Rodrigues (SFRH/BD/145736/2019), D.M. Silva (2020.06088.BD) and R. Pereira (2021.04850.BD) and a research contract to S. Ramos (DL57/2016/CP1344/CT0020).