Domestication and selective breeding for rapid-growth have impaired the cardiorespiratory system of salmonids, which might compromise their capacity to tolerate environmental stressors, such as heat waves. Exercise training by swimming has been proposed as a potential tool to enhance growth, cardiac function and disease resilience in farmed fish and thereby improves aquaculture production. However, whether exercise training could also improve cardiac robustness against heat waves, which are becoming more common and cause severe challenges to aquaculture, remains unknown. Here, we trained juvenile rainbow trout at three different training velocities: 0.06 m*s^-1 (or 0.9 body lengths per second [bl*s^-1]; control group), 0.11 m*s^-1 (or 1.7 bl*s^-1; medium speed group) and 0.17 m*s^-1 (or 2.7 bl*s^-1; high speed group) for 5 weeks, 6h per day, 5 days per week. Measuring maximal heart rate (fH_max) during acute warming, we demonstrated that training at 1.7 bl*s^-1 was optimal in order to increase the temperature at which fH_max reached its peak (T_peak) as well as the upper thermal tolerance of the cardiovascular function (arrhythmia temperature, T_ARR), up to 3.6°C as compared to the control fish. However, more intensive training did not provide similar improvement on thermal tolerance. Both training regimes enhanced the ventricular citrate synthase activity which may provide higher aerobic energy production capacity for ventricles. Further mechanistic studies are needed to understand the complex interactions between training intensities and changes in thermal tolerance. Although not conclusive on that point, our findings present a valid training programme for hatchery salmonids to increase their cardiac thermal tolerance and consequently probably also their capacity to tolerate heat waves, which has a direct application for aquaculture.

为实现快速生长而进行的驯化和选择性育种已经损害了鲑鱼的心肺系统，这可能会损害它们耐受环境压力的能力，例如热浪。游泳运动训练已被提议作为一种潜在的工具来增强养殖鱼类的生长、心脏功能和抗病能力，从而提高水产养殖产量。然而，运动训练是否也能提高心脏抵抗热浪的能力，这种热浪正变得越来越普遍，并对水产养殖造成严重挑战，目前尚不清楚。在这里，我们以三种不同的训练速度训练幼年虹鳟鱼：0.06 m*s ^-1（或每秒 0.9 身长 [bl*s ^-1 ]；对照组）、0.11 m*s ^-1（或 1.7 bl*s ^-1; 中速组）和 0.17 m*s ^-1（或 2.7 bl*s ^-1；高速组），持续 5 周，每天 6 小时，每周 5 天。测量最大心率 (FH _max ) 在急性变暖期间，我们证明了 1.7 bl*s ^-1的训练是最佳的，以增加FH _max达到峰值（T _peak）以及心血管功能的热耐受上限（心律失常温度，T _ARR)，与对照鱼相比，最高可达 3.6°C。然而，更密集的训练并没有提供类似的耐热性改善。两种训练方案都增强了心室柠檬酸合酶活性，这可能为心室提供更高的有氧能量产生能力。需要进一步的机制研究来了解训练强度和耐热性变化之间的复杂相互作用。尽管在这一点上尚无定论，但我们的研究结果为孵化场鲑鱼提供了一个有效的培训计划，以提高它们的心脏耐热性，从而提高它们耐受热浪的能力，这直接应用于水产养殖。