The efficiency and adaptive plasticity of mitochondrial metabolism is one of the key factors shaping organismal tolerance towards environmental change.We thus investigated the adaptive capacities of mitochondrial metabolism in Antarctic & Austral notothenioids (Nothothenia rossii, N. coriiceps & N. angustata) and temperate Sea Bass (Dicentrarchus labrax) with respect to some important factors that will influence the survival of marine life in the near future: global warming (elevated sea temperatures), ocean acidification (elevated CO2 levels) and hypoxia tolerance.We namely analysed the function and contribution of the single respiratory complexes to total mitochondrial metabolism, as well as membrane potential and proton leak. In all experiments, mitochondrial measurements were made under acute thermal challenges, compairing liver and heart mitochondria from either differently acclimated individuals (thermal acclimation, CO2 acclimation the combination thereof) or from individuals selected for a specific phenotypic trait (hypoxia tolerance in D. labrax).The implications of mitochondrial plasticity for long-term adaptation in a changing marine environment will be discussed.