Why do fish fail at high temperatures?

越来越多的证据表明，鱼类将受到全球气温上升的严重影响，因为它们的体温与周围水域的温度相匹配。这对淡水鱼来说是一个特别的问题，因为它们几乎没有移动到冷水中的空间。对鱼类温度上限的广泛引用的机械解释是，随着温度的升高，动物无法提供足够的氧气来满足其细胞不断增加的代谢需求。然而，最近对这一假设的测试发现，它通常不能正确预测温度上限，鱼类在氧气供应仍然充足的温度下失败。在本项目中，我们将使用新开发的方法首次对替代假设进行全面的检验，并由此提供可能的生理机制，以支持对温度升高对鱼类以及其他冷血水生物种的分布和功能的影响的预测。我们将测试鱼类的温度上限是否取决于线粒体-动物细胞的发电站-无法提供足够的能量分子ATP以使其细胞正常工作的点。以褐鳟为试验物种，我们将研究它们线粒体功能的变化是否能让我们预测它们仍能进食和生长的上限温度。我们还将测试生活在高温下的鱼类是否会像这个替代假设所预测的那样衰老得更快。该项目的信息将使我们能够预测哪些类型的鱼类最容易受到高温的影响，以及温度状况的哪些特征对生存最关键（例如，是日平均温度还是峰值温度）。如果我们要对物种或地点进行优先保护措施，就需要这些信息。

There is increasing evidence that fish will be badly affected by increases in global temperatures due to their body temperatures matching that of the surrounding water. This is a particular problem for freshwater fishes since they have little scope for moving to colder water. The widely-quoted mechanistic explanation for the upper temperature limit for fish is that, as the temperature rises, there comes a point where the animal cannot supply sufficient oxygen to meet the increasing metabolic demands of its cells. However, recent tests of this hypothesis have found that it often does not correctly predict upper temperature limits, with fish failing at a temperature when their supply of oxygen is still adequate. This suggests that the currently-adopted hypothesis is inadequate.In this project we will use newly-developed methods to provide the first comprehensive test of an alternative hypothesis, and in so doing potentially provide the physiological mechanism that will underpin predictions of the consequences of warming temperatures for the distribution and functioning of fish species - and potentially other cold-blooded aquatic species. We will test whether the upper temperature limit for fish is determined by the point at which their mitochondria - the powerhouses of animal cells - fail to deliver enough of the energy molecule ATP to allow their cells to function properly. Using Brown trout as a test species we will investigate whether the changing functioning of their mitochondria allows us to predict the upper temperature at which they can still feed and grow. We will also test whether fish living at high temperatures age faster, as is predicted by this alternative hypothesis. Information from this project will allow us to predict what types of species of fish will be most vulnerable to high temperatures and which features of the temperature regime are most critical to survival (e.g. whether it is the daily average or the peak temperature). This information is needed if we are to prioritise species or sites for protection measures.