Can Antarctic fish face marine heatwave-like events? Exploring cardiac physiology of Trematomus bernacchii using bio-loggers and stress biomarkers

Rising seawater temperatures fundamentally reshape marine ecosystems, with the Southern Ocean exhibiting vulnerability to climatic perturbations. Antarctic teleosts have evolved under near-constant sub-zero conditions, developing unique physiological adaptations. In this study, responses of Trematomus bernacchii , an endemic Antarctic fish, to three successive marine heatwave-like events were addressed. Using implantable bio-loggers, core body temperature and heart rate were monitored over 15 days, revealing a statistically significant positive correlation between core body temperature and cardiac performance, with an approximately 25% increase per °C. Molecular analyses of cardiac tissue revealed a sequential antioxidant response. An early upregulation of gpx4 suggests immediate mitochondrial protection against lipid peroxidation, while the subsequent induction of gpx1 , prdx3 , and prdx5 indicates a broader cytosolic defence. Furthermore, the marked decoupling between elevated gpx1 transcript levels and diminished Selenium-dependent glutathione peroxidase activity highlights a hitherto unrecognised post-transcriptional regulatory mechanism under acute thermal stress. Our findings suggest that T. bernacchii activates a sequential, organ-specific stress response to short-term warming, which may allow it to overcome episodic heatwaves. • First real-time cardiac activity monitoring with implantable bio-loggers in an Antarctic fish • Cardiac performance is a critical bottleneck for thermal tolerance. • Cardiac tissue mounted an early mitochondrial protection, followed by other cellular districts. • Mismatch between transcripts and proteins suggests a post-transcriptional regulation. • Trematomus bernacchii shows resilience margins against marine heatwaves.