Abstract

This study evaluated the oxidative stress response in two cold-water fish species, the Antarctic Harpagifer antarcticus and the sub-Antarctic H. bispinis, following exposure to single and combined stressors: polyvinyl chloride (PVC) microplastics and thermal increase. Fish were exposed for 24 h to two temperature regimes (2 ◦C and 5 ◦C for H. antarcticus; 8 ◦C and 12 ◦C for H. bispinis) and were orally administered a PVC microplastic solution (200 mg/L). Oxidative stress was assessed through transcriptional and enzymatic activity analyses of key antioxidant markers: catalase, glutathione peroxidase, superoxide dismutase, and glutathione reductase. In H. antarcticus, gill antioxidant gene expression decreased in response to both stressors when applied individually, while H. bispinis exhibited transcriptional upregulation under the same conditions. In H. antarcticus, enzymatic activity in gill tissues increased for all four enzymes following exposure to both microplastics and elevated temperature. In contrast, H. bispinis showed a differential enzymatic response: thermal stress induced CAT activity, whereas exposure to microplastics specifically increased GR activity. At the hepatic level, H. antarcticus displayed increased transcription of antioxidant genes following exposure to both stressors. In H. bispinis, transcriptional upregulation was limited to GR and SOD in response to microplastics. However, under the combined exposure of multiple stressors, an inactivation of the antioxidant enzyme response was observed in the gills. This could indicate a functional collapse of the antioxidant system under conditions of exacerbated acute stress. The observed responses raise concerns about the potential vulnerability of polar and subpolar fishes, considering their ecological importance in trophic networks and the increasing pressure from multiple anthropogenic stressors in a rapidly changing climate.