Abstract
Sustained swimming at moderate speeds is considered beneficial in terms of the productive performance of salmonids, but the causative mechanisms have yet to be unequivocally established. In the present study, the effects of moderate exercise on the bioenergetics of rainbow trout were assessed during a 15 week growth experiment, in which fish were reared at three different current speeds: 1 BL s−1, 0.5 BL s−1 and still water (≈ 0 BL s−1). Randomly selected groups of 100 fish were distributed among twelve 600 L tanks and maintained on a restricted diet regime. Specific growth rate (SGR) and feed conversion ratio (FCR) were calculated from weight and length measurements every 3 weeks. Routine metabolic rate (RMR) was measured every hour as rate of oxygen consumption in the tanks, and was positively correlated with swimming speed. Total ammonia nitrogen (TAN) excretion rates showed a tendency to decrease with increasing swimming speeds, yet neither they nor the resulting nitrogen quotients (NQ) indicated that swimming significantly reduced the fraction of dietary protein used to fuel metabolism. Energetic budgets revealed a positive correlation between energy expenditure and the current speed at which fish were reared, fish that were forced to swim and were fed restrictively consequentially had poorer growth and feed utilization. The results show that for rainbow trout, water current can negatively affect growth despite promoting minor positive changes in substrate utilization. We hypothesize that this may be the result of either a limited dietary energy supply from diet restriction being insufficient for both covering the extra costs of swimming and supporting enhanced growth.
Highlights
The use of a moderate water current, to elicit a low level of sustained aerobic exercise, can have beneficial effects on several parameters of productivity and welfare of farmed salmonids (McKenzie et al, 2012; Davison and Herbert, 2013)
Regardless of schooling, dominant fish may display less aggression to compensate for the higher energetic costs of swimming, which in turn increases the opportunities for subordinate individuals to feed (Christiansen and Jobling, 1990; Davison, 1997), and promotes growth by lowering stress levels in all categories of fish (Adams et al, 1995; Davison, 1997)
The purpose of the present study was to investigate the effects of water current on the growth performance and bioenergetics of rainbow trout maintained on a restricted diet, as a way to better expose the effects of exercise and prevent that differences in energy requirements be compensated and masked by an increased or differences in feed intake
Summary
The use of a moderate water current, to elicit a low level of sustained aerobic exercise, can have beneficial effects on several parameters of productivity and welfare of farmed salmonids (McKenzie et al, 2012; Davison and Herbert, 2013). Evidence for enhanced growth performance (East and Magnan, 1987; Houlihan and Laurent, 1987; Jobling et al, 1993; Jørgensen and Jobling, 1993; Davison, 1997) suggests that the additional costs of swimming are more than met by compensatory gains. The mechanisms underlying such effects seem to result from a number of physiological changes induced by the presence of water current. It is known that fish peripheral tissues have a poor ability to clear a www.frontiersin.org
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