Silva-Garay Lorena, Ern Rasmus, Andreassen Anna H, Reiersen Marie, Jutfelt Fredrik
Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway.
Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway; DTU Aqua: National Institute of Aquatic Resources, Technical University of Denmark, Kgs. Lyngby, Denmark.
J Therm Biol. 2025 Jul;131:104157. doi: 10.1016/j.jtherbio.2025.104157. Epub 2025 May 31.
Understanding the physiological mechanisms that limit the upper thermal tolerance of ectothermic animals during acute warming, particularly the role of tissue oxygen supply, is a key area of interest. Studies manipulating water oxygen levels show mixed results, suggesting that the effect of oxygen availability on upper thermal limits is species and context-dependent. Given the importance of thermal acclimation in modulating acute thermal limits, we investigated whether thermal acclimation impacts the oxygen dependence of Critical Thermal Maximum (CT) in adult zebrafish (Danio rerio). We conducted a series of three experiments. First, we measured routine and maximum metabolic rates and CT of 20°C-acclimated fish across four oxygen levels: 50, 100, 150, and 250 % air saturation to investigate the relationship between water oxygen level and aerobic scope. Second, we acclimated zebrafish to 20, 28, and 34°C for 13-17 days, and tested their CT under acute oxygen exposure (30, 100, 200 % air sat). Third, we expanded our sample size for fish acclimated to 14° and 20°C and assessed CT across the different oxygen levels. Thermal acclimation strongly influenced CT, with colder acclimation lowering CT (-6.2°C at 14°C, -2.7°C at 20°C) and warmer acclimation increasing it (+1.5°C at 34°C) relative to the optimal temperature (28°C). Hyperoxia did not increase CT at any acclimation temperature, despite significantly expanding their aerobic scope at 20°C. While hypoxia at 50 % air saturation did not reduce aerobic scope or CT, severe hypoxia (30 % air saturation) reduced CT across all acclimation temperatures. Our findings indicate that upper thermal limits in adult zebrafish are oxygen-independent across a broad range of oxygen levels, regardless of thermal history. Our study suggests that multiple temperature-sensitive physiological functions, rather than only the oxygen limitation mechanism, determines the acute upper thermal tolerance of fish.
了解在急性升温过程中限制变温动物热耐受上限的生理机制，尤其是组织氧气供应的作用，是一个关键的研究领域。控制水中氧气水平的研究结果不一，这表明氧气可用性对热耐受上限的影响因物种和环境而异。鉴于热驯化在调节急性热耐受极限方面的重要性，我们研究了热驯化是否会影响成年斑马鱼（Danio rerio）的临界热最大值（CT）对氧气的依赖性。我们进行了一系列三个实验。首先，我们测量了在20°C驯化的鱼在四种氧气水平下的常规代谢率和最大代谢率以及CT：空气饱和度的50%、100%、150%和250%，以研究水中氧气水平与有氧代谢范围之间的关系。其次，我们将斑马鱼分别驯化到20°C、28°C和34°C，持续13 - 17天，并在急性氧气暴露（空气饱和度的30%、100%、200%）下测试它们的CT。第三，我们扩大了适应14°C和20°C的鱼的样本量，并评估了不同氧气水平下的CT。热驯化对CT有强烈影响，相对于最佳温度（28°C），较冷的驯化降低了CT（14°C时降低6.2°C，20°C时降低2.7°C），而较温暖的驯化则提高了CT（34°C时提高1.5°C）。尽管在20°C时显著扩大了它们的有氧代谢范围，但高氧在任何驯化温度下都没有提高CT。虽然空气饱和度50%时的低氧没有降低有氧代谢范围或CT，但严重低氧（空气饱和度30%）在所有驯化温度下都降低了CT。我们的研究结果表明，无论热历史如何，成年斑马鱼在广泛的氧气水平范围内，其热耐受上限与氧气无关。我们的研究表明，多种温度敏感的生理功能，而不仅仅是氧气限制机制，决定了鱼类的急性热耐受上限。
