Environmental cocktails of pollutants leave morphological imprints on Seabream otoliths in Mediterranean lagoons.

Anthropogenic activities have led to the persistent build-up of trace metals and organic pollutants in coastal ecosystems, threatening aquatic life. Gilthead seabream, a commercially valuable species, often inhabits Mediterranean lagoons that function as vital nursery grounds. In this study, we examined 93 juvenile seabreams from three Tunisian lagoons to evaluate contamination levels and their effects on otolith morphology. We measured inorganic and organic contaminants in fish muscle and investigated their potential effects on otolith shape and asymmetry. Clear fish muscle contamination signatures emerged across sites: Tunis Lagoon exhibited the highest levels of contamination, followed by Ghar El Melh, while El Biban Lagoon appeared relatively pristine. Relatively elevated levels of metals (e.g., Pb, Ni, Be) and persistent organic pollutants (e.g., PCBs, DDTs, PBDEs) were observed in the more impacted lagoons. Notably, we found that otolith shape and fluctuating asymmetry were significantly associated with contaminant exposure, even after accounting for natural variables like fish size and lipid content. Specific pollutants, especially Cu, Rb, Sr and DDT, were linked to altered otolith morphology, suggesting disrupted biomineralization. The stronger response of the left otolith suggests that sub-lethal stress impairs developmental stability. Although fish muscle contaminant levels generally fell below food safety thresholds, the observed effects on otolith development raise concerns about functional consequences and underlying physiological stress. Our results highlight otolith asymmetry as a sensitive bioindicator of environmental stress in wild fish. By integrating shape analysis with contaminant profiling, this study offers a powerful tool for assessing pollution impacts in vulnerable Mediterranean nursery habitats.