Exercise, Stress and Welfare

Abstract

In this chapter we speculate about possible links between exercise and welfare in fish, drawing on the extensive mammalian literature on this topic. We summarise briefly some of the many studies reporting beneficial effects of sustained swimming, including faster growth, better feed conversion efficiency and lower plasma cortisol concentrations. While general trends are clear, in many of the studies reported here, there is considerable variation within each treatment group and we propose that one source of this variation may be the existence within populations of animals with distinct stress coping styles. These may determine how much individual fish can benefit from the stress-reducing effects of exercise through differences in cortisol responsiveness. Stress coping styles may also generate individual differences in the swimming speed that optimises growth, through differences in resting metabolic rate and general energy requirements. The various beneficial effects of exercise can all be seen as indicators of improved welfare, defined in terms of effective functioning. We discuss a number of possible reasons why exercise might promote welfare in fish. These including enhanced functional ability through improved muscular-skeletal development, osmoregulation and disease resistance, and hence better welfare by definition. Possible links between exercise and welfare also include behavioural changes, such as reduced aggression and, potentially, lower anxiety levels. They also include better spatial skills and an improved ability to predict adverse events arising from enhanced neurogenesis. In mammals, and possibly in fish also, the opportunity to undertake voluntary exercise is rewarding, which offers a possible link to feelings-based definitions of fish welfare.