Ectothermic animals are especially susceptible to temperature change, considering that their metabolism and core temperature are linked to the environmental temperature. As global water temperatures continue to increase, so does the need to understand the capacity of organisms to tolerate change. Sheepshead minnows (Cyprinodon variegatus) are the most eurythermic fish species known to date and can tolerate a wide range of environmental temperatures from − 1.9 to 43.0 °C. But little is known about the physiological adjustments that occur when these fish are subjected to acute thermal challenges and long-term thermal acclimation. Minnows were acclimated to 10, 21, or 32 °C for 4 weeks or acutely exposed to 10 and 32 °C and then assessed for swimming performance [maximum sustained swimming velocity (Ucrit), optimum swimming velocity (Uopt)] and metabolic endpoints (extrapolated standard and maximum metabolic rate [SMR, MMR), absolute aerobic scope (AS), and cost of transport (COT)]. Our findings show that the duration of thermal exposure (acute vs. acclimation) did not influence swimming performance. Rather, swimming performance was influenced by the exposure temperature. Swimming performance was statistically similar in fish exposed to 21 or 32 °C (approximately 7.0 BL s−1), but was drastically reduced in fish exposed to 10 °C (approximately 2.0 BL s−1), resulting in a left-skewed performance curve. There was no difference in metabolic end points between fish acutely exposed or acclimated to 10 °C. However, a different pattern was observed in fish exposed to 32 °C. MMR was similar between acutely exposed or acclimated fish, but acclimated fish had a 50% reduction in extrapolated SMR, which increased AS by 25%. However, this enhanced AS was not associated with changes in swimming performance, which opposes the oxygen-capacity limited thermal tolerance concept. Our findings suggest that sheepshead minnows may utilize two distinct acclimation strategies, resulting in different swimming performance and metabolic patterns observed between 10 and 32 °C exposures.

中文翻译：

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热适应或急性热暴露后羊头鲦鱼（Cyprinodon variegatus）的新陈代谢和游泳性能

考虑到它们的新陈代谢和核心温度与环境温度有关，等温动物特别容易受到温度变化的影响。随着全球水温持续升高，了解生物体耐受变化的能力的需求也不断增加。羊头鲦鱼 (Cyprinodon variegatus) 是迄今为止已知的最温热的鱼类，可以耐受 - 1.9 至 43.0 °C 的广泛环境温度。但是，当这些鱼受到急性热挑战和长期热适应时发生的生理调整知之甚少。鲦鱼在 10、21 或 32 °C 环境中适应 4 周或剧烈暴露于 10 和 32 °C，然后评估游泳性能 [最大持续游泳速度 (Ucrit)，最佳游泳速度 (Uopt)] 和代谢终点（外推标准和最大代谢率 [SMR、MMR)、绝对有氧范围 (AS) 和运输成本 (COT)]。我们的研究结果表明，热暴露的持续时间（急性与适应）不会影响游泳表现。相反，游泳性能受暴露温度的影响。暴露于 21 或 32 °C（约 7.0 BL s-1）的鱼的游泳性能在统计学上相似，但暴露于 10 °C（约 2.0 BL s-1）的鱼的游泳性能急剧下降，导致性能向左倾斜曲线。急性暴露或适应 10 °C 的鱼之间的代谢终点没有差异。然而，在暴露于 32 °C 的鱼中观察到不同的模式。急性暴露或驯化的鱼之间的 MMR 相似，但驯化的鱼外推的 SMR 降低了 50%，而 AS 增加了 25%。然而，这种增强的 AS 与游泳性能的变化无关，这与氧气容量有限的耐热性概念相反。我们的研究结果表明，羊头鲦鱼可能利用两种不同的适应策略，导致在 10 到 32°C 暴露之间观察到不同的游泳表现和代谢模式。