Department of Ocean Sciences, Memorial University, St. John's, NL, A1C 5S7, Canada.
J Therm Biol. 2021 Oct;101:103102. doi: 10.1016/j.jtherbio.2021.103102. Epub 2021 Sep 20.
Fish can be identified as either low responders (LR) or high responders (HR) based on post-stress cortisol levels and whether they exhibit a proactive or reactive stress coping style, respectively. In this study, male Atlantic salmon (Salmo salar) from 17 families reared at 9 °C were repeatedly exposed to an acute handling stress over a period of four months, with plasma cortisol levels measured at 1 h post-stress. Fish were identified as either LR or HR if the total Z-score calculated from their cortisol responses fell into the lower or upper quartile ranges, respectively; with intermediate responders (IR) classified as the remainder. Salmon characterized as LR, IR or HR were then subjected to an incremental thermal challenge, where temperature was raised at 0.2 °C day from their acclimation temperature (12 °C) to mimic natural sea-cage farming conditions during the summer in Newfoundland. Interestingly, feed intake remained high up to 22 °C, while previous studies have shown a decrease in salmon appetite after ∼16-18 °C. After the first three mortalities were recorded at elevated temperature, a subset of LR and HR salmon were exposed to another acute handling stress event at 23.6 °C. Basal and post-stress measurements of plasma cortisol, glucose and lactate did not differ between stress response phenotypes at this temperature. In the end, the average incremental thermal maximum (IT) of LR and HR fish was not different (25.1 °C). In comparison, the critical thermal maximum (CT; temperature increased at 2 °C h) of the remaining IR fish that had been held at 12 °C was 28.5 °C. Collectively, these results: 1) show that this population of Atlantic salmon is very thermally tolerant, and further question the relevance of CT in assessing responses to real-world temperature changes; and 2) indicate that characterization of stress phenotype at 9 °C is not predictive of their stress response or survival at high temperatures. Therefore, selection of fish based on phenotypic stress response at low temperatures may not be beneficial to incorporate into Atlantic salmon breeding programs, especially if the goal is to improve growth performance and survival at high temperatures in sea-cages.
鱼类可以根据应激后皮质醇水平以及是否表现出主动或被动应激应对方式，被鉴定为低反应者（LR）或高反应者（HR）。在这项研究中，来自 17 个家系的雄性大西洋鲑（Salmo salar）在 9°C 下饲养，经过四个月的时间，反复受到急性处理应激的影响，在应激后 1 小时测量血浆皮质醇水平。如果通过皮质醇反应计算得出的总 Z 分数落入较低或较高四分位范围，则将鱼类鉴定为 LR 或 HR；将中间反应者（IR）归类为其余部分。然后，将被鉴定为 LR、IR 或 HR 的鲑鱼置于递增的热挑战中，其中温度从适应温度（12°C）以 0.2°C/天的速度升高，以模拟纽芬兰夏季的自然海水养殖条件。有趣的是，在 22°C 之前，饲料摄入量一直保持高位，而之前的研究表明，在 16-18°C 之后，鲑鱼的食欲会下降。在升高的温度下记录到前三次死亡后，一部分 LR 和 HR 鲑鱼在 23.6°C 下再次经历急性处理应激事件。在该温度下，不同应激反应表型之间的基础和应激后血浆皮质醇、葡萄糖和乳酸水平没有差异。最后，LR 和 HR 鱼的平均递增热最大值（IT）没有差异（25.1°C）。相比之下，在 12°C 下饲养的其余 IR 鱼的临界热最大值（CT；温度以 2°C/h 的速度升高）为 28.5°C。总的来说，这些结果：1）表明该大西洋鲑种群非常耐热，进一步质疑 CT 在评估对现实世界温度变化的反应中的相关性；2）表明在 9°C 下对应激表型的特征描述不能预测其在高温下的应激反应或生存能力。因此，基于低温下表型应激反应选择鱼类可能不利于纳入大西洋鲑鱼的选育计划，特别是如果目标是提高海笼中高温下的生长性能和生存能力。
