The thermal stability of the Antarctic Ocean raises questions concerning the metabolic plasticity of Antarctic notothenioids to changes in the environmental temperature. In this study, Notothenia rossii survived 90days at 8°C, and their condition factor level was maintained. However, their hepatosomatic (0.29×) index decreased, indicating a decrease in nutrient storage as a result of changes in the energy demands to support survival. At 8°C, the plasma calcium, magnesium, cholesterol, and triglyceride concentrations decreased, whereas the glucose (1.91×) and albumin (1.26×) concentrations increased. The main energy substrate of the fish changed from lipids to glucose due to a marked increase in lactate dehydrogenase activity, as demonstrated by an increase in anaerobic metabolism. Moreover, malate dehydrogenase activity increased in all tissues, suggesting that fish acclimated at 8°C exhibit enhanced gluconeogenesis. The aerobic demand increased only in the liver due to an increase (2.23×) in citrate synthase activity. Decreases in the activities of superoxide dismutase, catalase, and glutathione-S-transferase to levels that are most likely sufficient at 8°C were observed, establishing a new physiological activity range for antioxidant defense. Our findings indicate that N. rossii has some compensatory mechanisms that enabled its long-term survival at 8°C.