## 3 Results and Discussion
### Identification and Quantification of MP Particles in Biota Samples Using Raman Spectroscopy
The average number of MPs items per gram weight in individuals containing MPs was higher in sea breams compared to sea bass. Specifically, sea breams contain 1.65 ng of PE per gram wet weight, 1.22 ng g\({}^{-1}\) EVA, 1.50 ng g\({}^{-1}\) PVB, 1.36 ng g\({}^{-1}\) PBMA, and 1.64 ng g\({}^{-1}\) PVA. Figure 2: Representative examples of microplastics Raman spectra detected in sea bass samples with micro-Raman spectroscopy. The present study also detected MP ingestion in mussels. According to Figure 4, PE was again the most frequent polymer type found (50%). Up next, ethylene-co-acrylic acid (EAA) was the second most commonly found polymer (45%), followed by EVA (40%) and PVB (25%). Additionally, Figure 4c,d represents the different sizes of the detected particles according to their diameter and perimeter. Ingested MPs have an average diameter of 15.1 \(\upmu\)m and a perimeter of 70.3 \(\upmu\)m. There was a much higher difference in the sizes of mussel samples than in fish species; specifically, four fibers were detected in mussels with sizes from 28.7 \(\upmu\)m to 86.1 \(\upmu\)m. The average number of MPs in mussels was 16 \(\pm\) 1.7 particles per mussel. The average number of ingested MPs in mussels per gram weight of this study was 6.65 ng g\({}^{-1}\) for EAA, 3.3 ng g\({}^{-1}\) for EVA, 1.18 ng g\({}^{-1}\) for PE, and 0.6 ng g\({}^{-1}\) for PVB. In addition, one of the samples contained two fibers corresponding to EAA with 1.62 ug g\({}^{-1}\) and 0.49 ug g\({}^{-1}\), respectively. More examples of representative examples of Raman spectra for MPs detected in marine organisms can be found in the Supplementary Materials. The composition pattern and number of the MPs found in sea basses clearly match with previous studies carried out in the Canary Islands region (Spain) regarding the determination of MPs in the marine environment. As an example, [PERSON] et al. (2021) [64] presented evidence of MP ingestion by cultured European sea bass (_Dicentrarchus labrav_), finding Cellulose (55%), Nylon (27%), fragments of PE (25%), and PP (25%) with an average of particles per fish (2.7 \(\pm\) 1.85). [PERSON] et al. (2018) [42] estimated the mean MP abundance in the wild European sea beams as 0.3 \(\pm\) 0.61 MPs fish\({}^{-1}\) from Portugal. When results obtained in this study were compared with wild counterparts, higher MP abundance (31 \(\pm\) 3.2 MPs fish\({}^{-1}\), 22 \(\pm\) 2.1 MPs sea bass\({}^{-1}\), and 40 \(\pm\) 3.9 MPs sea bream\({}^{-1}\)) were obtained, which may be related to exposure to the very homogeneous environmental conditions that occur in such fish farms. However, evidence from MPs contamination in commercial fish from the Mediterranean Coast of Egypt showed similar results to our findings, with PE (55%) and EVA (55%) as the dominant polymers in the fish digestive tracts  
Figure 3: (**a**) Identified particles of sea bream sample on silicon filters; (**b**) mean relative contribution of each polymer type; (**c,d**) size (diameter and perimeter, respectively) of MPs extracted from sea bream samples. of _Sparus aurata_ (38.3 \(\pm\) 28.4 items fish\({}^{-1}\)) with sizes \(\leq\) 50 \(\upmu\)m [65]. Furthermore, [PERSON] et al. (2021) [66] obtained nine different polymer types, including PE (45%) and polyvinyl esters (9%), with sizes ranging from 91 \(\upmu\)m to 5 mm and high average numbers of MP (8.53 \(\pm\) 2.19) in the intestine of _Sparus aurata_ comparable to our values. To our knowledge, polyvinyl esters such as polyvinyl butral and polybutyl methacrylate were detected for the first time in this study in the two fish species. Analogous findings of PBMA (2 MP fish\({}^{-1}\), 22%) and (2%) have been reported on Norwegian coast in Atlantic cod (_Gadus monthua_) and in three planktivorous species (_Clupea harengus_, _Sardina pilchardus_ and _Engarus encrasicolus_) of three different zones including the English Channel, the Northwestern Mediterranean Sea and the Northeastern Atlantic (Bay of Biscay), respectively [67; 68].