Is hypoxia vulnerability in fishes a by-product of maximum metabolic rate?

ABSTRACT The metabolic index concept combines data and known thermal sensitivities to estimate the factorial aerobic scope of animals in different habitats, which is valuable for understanding demands that constrain species' geographical distributions. An important assumption this O2 supply capacity (which equivalent rate oxygen consumption divided by environmental partial pressure oxygen: ) constant at tensions above critical threshold (i.e. where uptake can no longer meet demand). This has led notion hypoxia vulnerability not a selected trait, but by-product selection on maximum rate. In Commentary, we explore whether fundamental supported among fishes. We provide evidence all fishes, with some species exhibiting an elevated hypoxic environments. further discuss divergent selective pressures hypoxia- exercise-based cardiorespiratory adaptations while also considering implications hypoxia-optimized concept.