Hypoxia-seeking behavior, metabolic depression and skeletal muscle function in an amphibious fish out of water

Several animals enter a state of dormancy to survive harsh environmental conditions. During dormancy, metabolic depression can be critical for economizing on limited endogenous energy reserves. We used two isogenic strains (strain 1 and strain 2) of a self-fertilizing amphibious fish (Kryptolebias marmoratus) to test the hypothesis that animals seek hypoxic microhabitats that accentuate metabolic depression during dormancy. Fish were placed in custom experimental choice chambers that maintained an O2 gradient (normoxic to hypoxic) to determine the preferred O2 level of fish out of water. We then measured the O2 consumption rate of water- (control) and air-acclimated (21 days) fish in aerial normoxia, as well as the O2 consumption rate of air-acclimated fish acutely exposed to aerial hypoxia. We then tested the hypothesis that chronic hypoxia acclimation in air would protect endogenous energy reserves and skeletal muscle integrity, thereby maintaining locomotor performance. The hypothesis predicts that K. marmoratus acclimated to aerial hypoxia will deplete energy stores more slowly, demonstrate less skeletal muscle atrophy and have better locomotor performance than fish acclimated to aerial normoxia, presumably owing to hypoxic hypometabolism. We measured the whole-body [glycogen] and lipid content in fish acclimated to water (control), air and aerial hypoxia for 21 days. The cross-sectional area of red and white muscle fibers was also measured, as well as terrestrial locomotor performance (tail-flip jumping).

为应对严苛的环境胁迫，诸多动物会进入蛰伏状态。在蛰伏期间，代谢抑制对于节约有限的内源性能量储备至关重要。本研究选用两株同基因品系（品系1与品系2）的自体受精两栖鱼类斑纹隐小鳉（Kryptolebias marmoratus），以验证“动物在蛰伏期间会寻求能够强化代谢抑制的低氧微生境”这一假说。将实验鱼置于可维持氧气梯度（从常氧到低氧）的定制实验选择舱中，以测定离水状态下鱼类偏好的氧气浓度。随后，我们分别测定了水驯化（对照组）与空气驯化21天的实验鱼在空气常氧条件下的耗氧率，同时也测定了空气驯化鱼在急性暴露于空气低氧环境时的耗氧率。在此基础上，我们验证了另一项假说：在空气中进行慢性低氧驯化，能够保护鱼类的内源性能量储备与骨骼肌完整性，进而维持其运动能力。该假说预测，相较于空气常氧驯化的个体，经空气低氧驯化的斑纹隐小鳉（K. marmoratus）能量储备消耗速率更慢、骨骼肌萎缩程度更轻，且运动表现更优，这一差异推测源于低氧性代谢减退。我们测定了经水驯化（对照组）、空气驯化及空气低氧驯化21天的实验鱼的全身糖原与脂质含量。同时还测定了实验鱼的红肌与白肌纤维横截面积，以及其陆地运动能力（尾部翻转跳跃能力）。