Goldfish are among the champions of hypoxia tolerance, particularly at low water temperatures, but how their mitochondria respond to prolonged hypoxia is presently unknown. For instance, respiration capacity is decreased in the tissues of shovelnose ray sharks, oysters, and frogs, but maintained in epaulette sharks, killifish, and snappers. Mitochondrial respiration can be affected by hypoxia acclimation differently, depending on metabolic fuel, species, and tissue. Mitochondria are thought to play a key role in coordinating these responses because of their ability to detect changes in O 2. By contrast, hypoxia-tolerant animals can maintain this balance by regulating the activity of key enzymes of energy metabolism (e.g., slowing the tricarboxylic acid (TCA) cycle and stimulating glycolysis), and by downregulating ion pumps such as Na +/K +-ATPase. In hypoxia-sensitive species, this critical pathway of energy metabolism is inhibited when O 2 is scarce, causing an imbalance between the now lower supply of ATP and normal energetic demand.
Under normoxic conditions, adenosine triphosphate (ATP) is mainly produced by oxidative phosphorylation (OXPHOS) in the mitochondria through the electron transport chain (ETC). It presents a dangerous challenge requiring animals to enter a hypometabolic state for survival.
Hypoxia is a state of oxygen limitation commonly found in many environments.
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