Morphology, metabolism and behaviour: responses of three fishes with different lifestyles to acute hypoxia

Behavioural responses to changing environments affect community composition, so the identification of associations between environmental gradients, behavioural traits and physiological traits makes a significant contribution to the quest for trait‐based rules of community change. We tested the hypothesis that fish morphology and lifestyle are associated with metabolic rate, hence oxygen demand, and behavioural response to gradual hypoxia [low dissolved oxygen (DO)], using respirometry and behavioural experiments. Three species fell along different points of the fast–slow lifestyle continuum: Melanotaenia fluviatilis, a pelagic fish adapted to endurance swimming, lies at the fast end of the lifestyle continuum, while Mogurnda adspersa, a benthic fish adapted to burst swimming, lies at the other end. The benthopelagic Hypseleotris sp. has an intermediate lifestyle. Standard and routine metabolic rates varied strongly among the species and were associated with lifestyle according to the inequality M. fluviatilis > Hypseleotris > M. adspersa. As DO declined, aquatic surface respiration behaviour also varied significantly among the species and indicated a sensitivity to hypoxia described by the same inequality. As hypoxia ensued, changes in habitat were also linked to lifestyle, but changes in activity level among species were not neatly correlated with lifestyle. Overall, our experiments imply that there are significant links between morphology, lifestyle, metabolism and behavioural response to hypoxia in these three species of fish.