Response of Atlantic salmon to long-term sustained aerobic training at suboptimum elevated temperature: Cardiac anatomy, aerobic performance, and growth implications

Sustained aerobic training is suggested to enhance cardiac performance and growth in farmed salmonids, but its effects under suboptimum elevated temperatures remain unclear. This study examined whether continuous training at different temperatures could improve growth and whether it influenced cardiac performance at a suboptimum elevated temperature in a context relevant to offshore aquaculture. Atlantic salmon were reared for 90 days at 15 °C (control temperature) and 20 °C (suboptimum elevated temperature), with either continuous aerobic swimming (trained: 0.45 m.s^-1) or standard conditions (untrained: 0.18 m.s^-1). Growth and feed intake were assessed at both temperatures, while cardiac and metabolic parameters were measured only at 20 °C. At 15 °C, trained fish exhibited increased feed intake, but this did not translate into improved growth. At 20 °C, neither feed intake nor growth improved with training. Swim-tunnel respirometry at 20 °C revealed no significant differences in aerobic performance between trained and untrained fish, although trained fish exhibited lower interindividual variability in metabolic and swimming parameters. While training increased relative ventricular mass (RVM), indicating potential cardiac remodelling, this did not result in improved metabolic performance. These findings underscore the complexity of physiological responses to exercise and temperature in salmon aquaculture. While continuous aerobic training induced minor cardiac adaptations, its impact on growth and performance was limited, particularly at suboptimum elevated temperatures. This research provides valuable insights into how Atlantic salmon may respond to offshore farming environments, with specific relevance to Tasmania's aquaculture industry.