Ecophysiology of Antarctic fish. Stress responses to environmental global changes

Dealing with stressful situations is a challenge all living organisms experience and must overcome. The ability to develop strategies to cope with stress is thus essential for survival and reproductive success. In Antarctic organisms, stress responses are particularly relevant because many fish have evolved narrow physiological tolerances, reflecting long adaptation to stable environments, which makes them sensitive to rapid environmental change. Among them, Antarctic notothenioid fishes are an outstanding example, as their extreme specialization to the cold and stable Southern Ocean leaves them with little physiological flexibility when confronted with novel stressors. Although geographically isolated, Antarctica is not immune to the consequences of human activity. Anthropogenic pressures reach this remote environment directly, through the long-range transport and accumulation of pollutants, and indirectly, as major drivers of global climate change. The Antarctic Polar Front limits maritime transfer of contaminants, making atmospheric transport the principal pathway by which xenobiotics reach the Southern Ocean. Despite the vast distance from pollution sources, metals and emerging pollutants, including endocrine-disrupting chemicals and perfluorinated compounds (PFAS), have been detected in the Antarctic ecosystems. While the toxicological potential of many of these substances is well established, their environmental fate and biological effects in polar regions remain poorly represented in monitoring programmes. In parallel, climate change poses a severe additional challenge for high-latitude species, such as Antarctic notothenioid fishes, which are particularly vulnerable to ocean warming, oxygen levels, acidity etc. Processes such as glacier melting and freshwater influx profoundly alter salinity, temperature, circulation patterns, and sea level, leading to osmotic stress and ecosystem shifts. Because the Antarctic ice sheet functions as the largest cold reservoir of the Earth system, these changes not only reshape local ecosystems but also influence climate globally. Despite its remoteness, Antarctica is increasingly affected by global change, making it a unique natural laboratory to investigate how pollutants and climate-driven stressors shape biological responses. This context provides an exceptional opportunity to study stress physiology in highly specialized organisms that are predicted to be among the most vulnerable to environmental change. Against this backdrop, the investigation of stress physiology in Antarctic notothenioid fishes at multiple biological levels forms the core of my thesis. This multi-layered approach, addressing molecular and physiological mechanisms of stress, is mirrored in the structure of this work. Thereby, it focuses on neuroendocrine signalling, metabolic adjustments, cardiac performance, and the generation and detoxification of reactive oxygen species (ROS). Building on this, I examined the role of antioxidant enzymes, metallothioneins, and oxidative damage biomarkers, and explored the interplay between oxidative stress and immune modulation. Particular attention was given to post-transcriptional regulation and stress memory, including stress granules and epigenetic responses (Section I). The second part (Section II) of the thesis positioned these mechanisms within the broader environmental context of the Southern Ocean, considering the combined pressures of climate change and anthropogenic pollutants such as heavy metals, PFAS, and BPA. Finally, the experimental chapters (Section III) integrate these perspectives through targeted studies, addressing thermal stress, pollutant exposure, transcriptional plasticity, and post-transcriptional regulation in key Antarctic fish species.