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What we did: Hypoxic environments can be very different from one another. For example, tidepools experience short-term bouts of severe hypoxia, whereas oceanic oxygen minimum zones experience moderate hypoxia all year round. We hypothesized that this variation in naturally occurring hypoxia explains the seemingly innumerable ways that fishes tolerate hypoxia. To explore this, we devised a 4-quadrant matrix that binned natural hypoxic environments according to their oxygen levels and hypoxic duration characteristics, and then systematically mined the literature for well-studied species native to these environments.
What we found: Distantly related species from similar hypoxic environments employ similar metabolic strategies of hypoxic survival, while closely related species from dissimilar hypoxic environments employ dissimilar strategies. Predation threat and aerial access also contribute to the strategies used.
What this means: By suggesting that the wide variation in metabolic responses of fishes to hypoxia is not random but rather based on the native hypoxic environment, this work establishes the importance of considering hypoxia as a complex, multi-dimensional stressor. Refined models may even be capable of predicting optimal hypoxic responses based on environmental variables, and this may benefit conservation efforts as the world’s aquatic environments become increasingly hypoxic.