Abstract The ability to conserve energy by suppressing metabolic rate is an essential component of staying alive during exposure to environmental hypoxia. These energetic savings can be achieved through hypoxia-induced changes to behavior, physiology, and cellular processes, which serve to bring whole organism energy consumption more in line with the reduced capacity for energy production. During hypoxia exposure, the main site of energy production, the mitochondria, is slowed (during hypoxia) or not running at all (during anoxia), because of the lack of oxygen, which is the final substrate for mitochondrial respiration. Suppression of metabolic rate has been documented in many fish species in response to hypoxia exposure. This article describes the beneficial aspects of metabolic rate suppression as response to hypoxia exposure and outlines the underlying mechanisms that yield reductions in energy expenditure.