Temperature is a key factor shaping performance of ectothermal organisms. Furthermore, their thermal tolerance windows may be narrowed by the ongoing process of ocean acidification. Consequently, these organisms may become even more sensitive to warming. As mitochondrial metabolism is one of the most important factors defining thermal limitation, we studied the effects of acclimation to elevated temperatures (7°C), elevated CO2-levels (1190µatm) and the combination thereof on mitochondrial plasticity of the Antarctic fish Notothenia rossii.Mitochondrial metabolism was determined from measurements of mitochondrial respiration, membrane potential and proton leakage. Measurements of standard metabolic rate were taken for analysis of potential aerobic limitations in this Antarctic notothenioid.This study is the first dealing with metabolic sensitivity of the Antarctic fish Notothenia rossii to hypercapnia and the combined effect of warming and elevated CO2-levels.