The amazon fishes’ responses to hypoxia seem to be related to the Amazon basin diversity of aquatic environments, which present drastic daily and seasonal variations in the dissolved oxygen concentration. Among these fishes’ adaptation to hypoxia, behavioral, metabolic, physiological, and biochemical responses are well known for some species. In this work, we aimed to identify how two different aquatic environments, normoxic forest streams and hypoxic lakes, dictate the responses to hypoxia for two cichlid species, Mesonauta festivus and Aequidens pallidus. In our results, we found that A. pallidus is less tolerant to hypoxia, which seems to be related to this animal’s natural normoxic environment. Even though this species modulated the mitochondrial respiration in order to improve the oxygen use, it also showed a lower decrease in metabolic rate when exposed to hypoxia and no activation of the anaerobic metabolism. Instead, M. festivus showed a higher decrease in metabolic rate and an activation of the anaerobic metabolism. Our data reveal that the natural dissolved oxygen influences the hypoxia tolerance and the species’ tolerance is related to its ability to perform metabolic depression. The interest results are the absence of mitochondrial respiration influences in these processes. The results observed with A. pallidus bring to light also the importance of preserving the forests, in which streams hold very specialized species acclimated to normoxia and lower temperature. The importance of hypoxia tolerance is, thus, important to keep fish assemblage and is thought to be a strong driver of fish biodiversity.

亚马逊鱼对缺氧的反应似乎与亚马逊流域水环境的多样性有关，其溶解氧浓度呈现出剧烈的每日和季节性变化。在这些鱼类对缺氧的适应中，一些物种的行为、代谢、生理和生化反应是众所周知的。在这项工作中，我们旨在确定两种不同的水生环境（含氧量正常的森林溪流和缺氧湖泊）如何决定两种慈鲷物种Mesonauta festivus和Aequidens pallidus对缺氧的反应。在我们的结果中，我们发现A. pallidus对缺氧的耐受性较差，这似乎与这种动物的天然常氧环境有关。尽管该物种调节了线粒体呼吸以改善氧气的使用，但它在暴露于缺氧和无氧代谢没有激活时也表现出较低的代谢率下降。相反，M. festivus表现出更高的代谢率下降和无氧代谢的激活。我们的数据表明，天然溶解氧会影响缺氧耐受性，而物种的耐受性与其进行代谢抑制的能力有关。有趣的结果是在这些过程中没有线粒体呼吸影响。用A. pallidus观察到的结果还揭示了保护森林的重要性，在这些森林中，溪流中有非常特殊的物种适应了常氧和较低的温度。因此，耐缺氧性对于保持鱼类群落非常重要，并且被认为是鱼类生物多样性的强大驱动力。