The visual capacity of aquatic organisms is, in general, related to light penetration in the water. Therefore, aquatic environments that differ in color can potentially contribute to species polymorphism, especially in fish. In this study, we explore the relationship between light quality and intensity in water bodies and the eye and mouth size in Galaxias maculatus, one of the most widespread fish. Fish morphology was studied photographically, and the vertical attenuation coefficient of light (Kd) was measured in five aquatic systems: two humic lakes, two estuaries, and one river. Water color was also estimated as absorbance at 440 nm. In those environments with less light penetration and darker water color, we observed bigger eyes and, additionally, larger mouths. The darkness of water bodies was mainly related to water color associated with humic substances. As G. maculatus is known to be a visual predator, our results suggest that bigger eyes increase visual capacity in darker environments, which would result in improved feeding rates, also supported by larger mouth length.

中文翻译：

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广泛存在的鱼 Galaxias maculatus 的形态差异：较暗的环境是否意味着更大的眼睛？

一般来说，水生生物的视觉能力与水中的光线穿透力有关。因此，颜色不同的水生环境可能会导致物种多态性，尤其是在鱼类中。在这项研究中，我们探讨了水体中的光质量和强度与黄斑星河鱼（最普遍的鱼类之一）的眼睛和嘴巴大小之间的关系。对鱼类形态进行了摄影研究，并在五个水生系统中测量了光的垂直衰减系数 (Kd)：两个腐殖质湖、两个河口和一条河流。水的颜色也被估计为 440 nm 处的吸光度。在那些光线穿透较少、水色较深的环境中，我们观察到更大的眼睛，此外还有更大的嘴巴。水体的黑暗主要与腐殖质相关的水体颜色有关。由于 G. maculatus 是一种视觉捕食者，我们的研究结果表明，在较暗的环境中，更大的眼睛会增加视觉容量，这将导致进食率提高，同时嘴巴更长。