Organic and Inorganic Pollutants, Oxidative Stress Biomarkers, and Electrophoretic Protein Profiles in an Endangered Thresher Shark ( <i>Alopias vulpinus</i> ) From Southeastern Brazil: A Case Study

A comprehensive screening of different environmental contaminants (total metals, thermostable metal fractions associated with detoxification, and persistent organic pollutants) was conducted in an endangered common thresher shark (Alopias vulpinus ) individual incidentally captured in southeastern Brazil. Stress biomarkers were assessed to evaluate physiological responses, and SDS-PAGE was applied to identify thermostable protein profiles. Most metals were more abundant in total than in thermostable fractions, suggesting partial cellular absorption, likely through compartmentalization in organelles or binding to metallothioneins. Of 25 screened pesticides, only p,p'-DDT and Mirex were detected, with unexpectedly high levels observed in liver. Several low molecular weight PAHs were also found in both tissues, especially muscle, suggesting chronic exposure and bioaccumulation. The SDS-PAGE revealed ~15 kDa bands, consistent with metallothioneins, and higher bands possibly corresponding to matrix metalloproteinases. Poor resolution in the Ampullae of Lorenzini was likely due to high salt content. Antioxidant biomarkers showed tissue-specific patterns, with high H₂O₂ levels and SOD activity in gills, blood, and brain, suggesting oxidative stress. Further studies are, however, required, as a sample number of one precludes broad conclusions at the species level. Despite this limitation, the study provides valuable preliminary insights and a baseline for Alopias spp. The integrated biochemical and molecular approach applied herein may aid in detecting early physiological stress and sublethal contamination effects and, combined with ecological and life-history data, can inform conservation strategies, such as habitat prioritization, pollutant mitigation, and monitoring programs, to support the long-term survival and population viability of this and other vulnerable shark species.