Tolerance of an acute warming challenge declines with size in Nile tilapia: evidence of a link to capacity for oxygen uptake

It has been proposed that larger individuals within fish species may be more sensitive to global warming, due to limitations in their capacity to provide oxygen for aerobic metabolic activities. This could affect size distributions of populations in a warmer world but evidence is lacking. In Nile tilapia Oreochromis niloticus (n = 18, mass range 21 - 313g), capacity to provide oxygen for aerobic activities (aerobic scope) was inde-pendent of mass at an acclimation temperature of 26 °C. Tolerance of acute warming, however, declined significantly with mass when evaluated as the critical temperature for fatigue from aerobic swimming (CTSmax). The CTSmax protocol challenges a fish to meet the oxygen demands of constant intense aerobic exercise while their demands for basal metabolism are accelerated by incremental warming, culminating in fatigue. CTSmax elicited pronounced increases in oxygen uptake but maximum rates achieved prior to fatigue declined very significantly with mass. Mass-related variation in CTSmax and maximum oxygen uptake rates were positively correlated, which indicates a caus-al relationship. When fish populations are faced with acute thermal stress, larger indi-viduals may become constrained in their ability to perform aerobic activities at lower temperatures than smaller conspecifics. This could affect survival and fitness of larger fish in a world with more frequent and extreme heatwaves, with consequences for population productivity.
Methods
The data were collected on 18 tilapia acclimated to 26 °C, swimming respirometry was used to calculate standard and active metabolic rates, to calculate aerobic scope by difference. CTmax was measured by warming groups of animals in a tank until loss of equilibrium, CTSmax was measured by warming tilapia when they were swimming, until they fatigued. Data are calculated values, not raw oxygen data (for example).
Also included are data for swimming performance at acclimation temperature, namely maximum aerobic speed, absolute maximum speed and the gait transition speed between these.
Further, the measures of oxygen uptake during incremental warming in CTSmax are carried for each fish studied.

有研究表明，鱼类物种中体型较大的个体可能对全球变暖更为敏感，这主要归因于其在提供氧气以支持有氧代谢活动方面的能力限制。这一现象可能会影响温暖世界中鱼类种群的大小分布，然而相关证据尚显不足。在尼罗罗非鱼（Oreochromis niloticus，n = 18，体重范围21 - 313g）中，在适应温度为26°C时，提供氧气以支持有氧活动的范围（有氧广度）与体重无关。然而，当以从有氧游泳疲劳（CTSmax）的临界温度来评估时，对急性变暖的耐受性却随着体重的增加而显著下降。CTSmax测试挑战鱼类在保持基础代谢需求加速的同时，满足持续高强度有氧运动的氧气需求，最终导致疲劳。CTSmax测试引发氧摄取量显著增加，但在疲劳前的最大摄取速率却与体重呈显著负相关。CTSmax和最大氧摄取速率与体重相关的变化呈正相关，这表明了因果关系。当鱼类种群面临急性热应激时，大型个体可能在低于小型同种个体的温度下，其进行有氧活动的能力受到限制。这可能会影响大型鱼类在更频繁且更极端热浪的世界中的生存和适应性，从而对种群生产力产生影响。

研究方法：在26°C下对18条罗非鱼进行适应，使用游泳呼吸测量法计算标准代谢率和活性代谢率，通过差分法计算有氧广度。CTmax通过加热鱼缸中的动物群体至失去平衡来测量，CTSmax通过加热游泳的罗非鱼，直至其疲劳来测量。数据为计算值，而非原始的氧气数据（例如）。此外，还包括在适应温度下的游泳性能数据，即最大有氧速度、绝对最大速度以及这些速度之间的步态转换速度。此外，还对每条研究的鱼类在CTSmax中增量加热时的氧摄取量进行了测量。