The ability to tolerate environmental change may decline as fishes age. We tested the hypothesis that ageing influences the scope for phenotypic flexibility in the mangrove rivulus (Kryptolebias marmoratus), an amphibious fish that transitions between two vastly different environments, water and land. We found that older fish (4–6 years old) exhibited marked signs of ageing; older fish were reproductively senescent, had reduced fin regenerative capacity and body condition, and exhibited atrophy of both oxidative and glycolytic muscle fibers relative to younger adult fish (1–2 years old). However, age did not affect routine O2 consumption. We then acclimated adult fish (1–6 years) to water (control) or air for 10 days to assess the scope for phenotypic flexibility in response to terrestrial exposure. In support of our hypothesis, we found that older air-acclimated fish had a diminished scope for gill remodeling relative to younger fish. We also found that older fish exhibited poorer terrestrial locomotor performance relative to younger adult fish, particularly when acclimated to air. Our results indicate that ageing diminishes skeletal muscle integrity and locomotor performance of amphibious fishes, and may, therefore, impair terrestrial foraging ability, predator avoidance, or dispersal across the terrestrial environment. Remarkably, older fish voluntarily left water to a similar degree as younger fish despite the age-related deterioration of traits important for terrestrial life.

中文翻译：

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老化影响空气适应的两栖鱼的表型灵活性

随着鱼类年龄的增长，耐受环境变化的能力可能会下降。我们检验了衰老影响红树林河 (Kryptolebias marmoratus) 表型灵活性范围的假设，这是一种在水和陆地两种截然不同的环境之间过渡的两栖鱼类。我们发现年龄较大的鱼（4-6 岁）表现出明显的衰老迹象；与年轻的成年鱼（1-2 岁）相比，年长的鱼在生殖上衰老，鳍的再生能力和身体状况降低，氧化和糖酵解肌肉纤维都出现萎缩。然而，年龄并不影响常规 O2 消耗。然后，我们将成年鱼（1-6 岁）适应水（对照）或空气 10 天，以评估表型灵活性对陆地暴露的反应范围。为了支持我们的假设，我们发现，相对于较年轻的鱼，较老的适应空气的鱼的鳃重塑范围较小。我们还发现，与年轻的成年鱼相比，年长的鱼表现出较差的陆地运动性能，尤其是在适应空气时。我们的研究结果表明，衰老会降低两栖鱼类的骨骼肌完整性和运动性能，因此可能会损害陆地觅食能力、避免捕食者或在陆地环境中的分散。值得注意的是，年长的鱼自愿离开水的程度与年幼的鱼相似，尽管与年龄相关的对陆地生命很重要的性状退化。我们还发现，与年轻的成年鱼相比，年长的鱼表现出较差的陆地运动性能，尤其是在适应空气时。我们的研究结果表明，衰老会降低两栖鱼类的骨骼肌完整性和运动性能，因此可能会损害陆地觅食能力、避免捕食者或在陆地环境中的分散。值得注意的是，年长的鱼自愿离开水的程度与年幼的鱼相似，尽管与年龄相关的对陆地生命很重要的性状退化。我们还发现，与年轻的成年鱼相比，年长的鱼表现出较差的陆地运动性能，尤其是在适应空气时。我们的研究结果表明，衰老会降低两栖鱼类的骨骼肌完整性和运动性能，因此可能会损害陆地觅食能力、避免捕食者或在陆地环境中的分散。值得注意的是，年长的鱼自愿离开水的程度与年幼的鱼相似，尽管与年龄相关的对陆地生命很重要的性状退化。