Microplastic Pollution and Its Physiological Effects on the Top Fish Predator Dentex dentex from the Western Mediterranean

Microplastic (MP) pollution is a growing environmental concern, particularly in marine ecosystems. This study investigated the presence and effects of MPs in the common dentex (Dentex dentex), a commercially and ecologically important species in the Mediterranean Sea. Fish (n = 22) were collected from Ibiza’s coastal waters (western Mediterranean, Spain), and their gastrointestinal tracts were analysed to determine MP ingestion rates and potential physiological impacts. MPs were detected in 90.9% of the specimens, with an average of 6.6 ± 1.2 MPs per individual. Fibres accounted for 78.9% and fragments for 21.1%. Stress and detoxification biomarkers were assessed by categorizing fish into two groups based on MP load: low (<6 MPs) and high (≥6 MPs). Fish with higher MP loads showed significantly increased detoxification and antioxidant enzyme activities in the digestive tract, while malondialdehyde levels remained similar between groups. No significant differences were observed in liver biomarkers. These findings indicate that MP ingestion triggers physiological responses in D. dentex, activating antioxidant and detoxification defences in the digestive tract. However, the lack of response in the liver suggests that the MP load is not sufficient to induce systemic changes. Further research is needed to assess long-term consequences on fish health and ecosystem sustainability.