The effect of hypoxia on fish swimming performance and behaviour.

Oxygen depletion, hypoxia, can be a common stressor in aquatic habitats, including aquaculture. Hypoxia limits aerobic swimming performance in fish, by limiting their aerobic metabolic scope. Hypoxia also elicits changes in spontaneous swimming activity, typically causing a decrease in swimming speed in sedentary species and an increase in active species. However, fish do have the capacity to avoid hypoxia and actively choose well-oxygenated areas. Hypoxia causes differences in fish behaviour in schools, it may reduce school density and size and influence activities such as shuffling within schools. Hypoxia also influences predator[long dash]prey interactions, in particular by reducing fast-start performance. Thus, through effects on swimming, hypoxia can have profound effects on species distributions in the field. In aquaculture, effects of hypoxia may be particularly significant in sea cages. It is therefore important to understand the nature and thresholds of effects of hypoxia on swimming activity to extrapolate to potential impacts on fish in aquaculture.