## 4 Conclusions  
Overall, this study provides information on the quantities and types of MPs in sea basses (_Clientrarchus labrax_) and sea breams (_Sparus aurata_), as well as mussels (_Mytillus galloprovincialis_), from the aquaculture environment of the Northwest Ionian Sea as well as in seawater. PE was the most frequent polymer type found in fish and mussels in consistency with MPs in seawater, reflecting the global production and use of this material. MP ingestion values are comparable to those reported for the same species in other Mediterranean areas. It also documents, for the first time, the detection of PVB (25%) and PBMA (25%) polymers in that kind of fish species. Most MPs sampled in seawater were in the shape of fibers and fragments. A carbonylation index > 0.31 in the analyzed polymers from seawater samples proves the chemical weathering resulting from photo-oxidation and/or bacterial degradation. Weathering and fragmentation processes were observed in the images obtained from SEM, while oxidation and sorption of metallic ions were further confirmed by EDS analysis. Finally, our results can contribute to the definition of baseline levels of MP ingestion in the studied species as well as to the MP pollution in the Mediterranean area.  
Figure 11: EDS spectra of six selected MPs recovered from fish guts (**a**) F1, F2, F3 and (**b**) F4, F5, F6. Spectra were acquired using an accelerating voltage of 15 kV.  
**Supplementary Materials:** The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app13179705/s1](https://www.mdpi.com/article/10.3390/app13179705/s1)]([https://www.mdpi.com/article/10.3390/app13179705/s1](https://www.mdpi.com/article/10.3390/app13179705/s1)); Figure S1: The stepwise workflow employed in this study to extract efficiently microplastics from fish and mussels. Figure S2: Representative examples of Raman spectra for microplastics detected in sea beam samples with micro-Raman spectroscopy. Figure S3: Representative examples of Raman spectra for microplastics detected in mussel samples with micro-Raman spectroscopy. Figure S4: Representative examples of Raman spectra for microplastics detected in seawater samples with micro-Raman spectroscopy.  
**Author Contributions:** Investigation, visualization, validation, formal analysis, writing--original draft preparation, K.M. and C.L.; methodology, formal analysis, A.G.K.; conceptualization, methodology, supervision, resources, writing--review and editing, funding acquisition, I.K. All authors have read and agreed to the published version of the manuscript.  
**Funding:** The authors would like to acknowledge the financial support of the project \"Development of research infrastructure for the design, production, development of quality characteristics and safety of agrofoods and functional foods (RI-Agrofoods)\" (MIS 5047235), which is implemented under the Action \"Reinforcement of the Research and Innovation Infrastructure\", funded by the Operational Programme \"Competitiveness, Entrepreneurship and Innovation\" (NSRF 2014-2020) and co-financed by Greece and the European Union (European Regional Development Fund).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The data presented in this study are available in this article and in the associated Supplementary Materials.  
**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.