The frequency and magnitude of droughts are forecast to increase throughout southern Australia, which implies our freshwater fishes will potentially face more frequent and severe episodes of hypoxia in the future. Unfortunately, however, we have a poor understanding of the resistance and resilience of our fishes to hypoxia. More generally, there appear to be few generalisations or ‘laws’ of fish community change in response to hypoxia; laws that ecologists and managers can utilise to forecast effects on biodiversity. Community ecologists have suggested that experimental work linking animal physiological traits to fitness along environmental gradients may yield more useful, ‘functional-trait-based’ laws of community change.

Here we tested the hypothesis that fish ‘lifestyle’ is linked to metabolic rate, which in turn drives resistance, and behavioural response, to hypoxia. Metabolic rates of a ‘fast’ pelagic species, unspecked hardyhead, were significantly higher than those of a ‘slow’ benthopelagic ambush predator, flathead gudgeon. In turn, physiological resistance to hypoxia (as indicated by critical oxygen tension) was lower in hardyhead than in flathead gudgeon. Behavioural responses to gradual hypoxia also demonstrated that the onset of avoidance to hypoxia occurred earlier in hardyhead than in flathead gudgeon. These results, combined with others, imply interesting links between fish lifestyle and resistance to hypoxia.