Physiological Responses to Microplastic Ingestion in the Peacock Wrasse Symphodus tinca from Ibiza, Spain

Microplastics (MPs) are ubiquitous coastal contaminants that can induce oxidative stress, detoxification responses and inflammation in marine species. We evaluated MP occurrence and associated physiological responses in the digestive tract of the peacock wrasse Symphodus tinca (N = 28) from the northeastern coast of Ibiza (Balearic Islands, Spain). MPs occurred in 60.7% of the fish (58 items in total; mean 2.1 ± 0.5 items·fish−1), dominated by fibres (75.9%). Polyester (38.1%) and polypropylene (23.8%) were the most frequent polymers in the subset of MPs analysed. Fish were grouped by median MP count (<2 vs. ≥2), and statistical differences and correlations were assessed. Individuals with ≥2 MPs showed significantly elevated activities of antioxidant enzymes (catalase, CAT; superoxide dismutase, SOD), the phase-II detoxification enzyme glutathione S-transferase (GST), and the pro-inflammatory enzyme myeloperoxidase (MPO). Production of reactive oxygen species (ROS) and oxidative-damage biomarkers, malondialdehyde (MDA) and protein carbonyls tended to be higher in the high-MP group, but differences were not statistically significant. MP exposure correlated positively with all biomarkers except protein carbonyls. In conclusion, higher MP loads in S. tinca are associated with activation of antioxidant, detoxification and inflammatory pathways, without clear evidence of widespread oxidative damage under the sampled conditions. These physiological responses suggest potential impacts on individual fitness that may signal early ecological effects in coastal fish populations, highlighting their value as early-warning indicators in coastal monitoring and environmental management.