The eye size of the bluefin killifish (Lucania goodei) varies from springs to swamps

Variation in lighting environments creates different demands of visual systems for the successful detection and interpretation of visual signals in a given setting. Eye size is a critical property of the visual system as it is has strong effects on visual acuity and visual sensitivity. While many comparative studies have examined eye size across fishes that live in disparate lighting environments (i.e., caves versus surface habitats, mesopelagic versus pelagic depths, turbid versus clear water), fewer have investigated differences in eye size as a function of water clarity at the among population - within species level. Here, we compared relative eye size (eye size residuals on standard length) between wild-caught individuals from swamps and springs and across four drainages in Florida. We also performed a laboratory experiment where we reared animals in clear or tea-stained water, which mimic spring and swamp conditions to determine whether phenotypic plasticity as a function of lighting conditions influences relative eye size. Field caught animals greatly varied in relative eye size among populations, but there was no clear relationship with lighting environment. Fish from southern populations (where swamps are common) had greater relative eye size than those from northern populations (where springs are common). However, in North Florida, bluefin killifish from swamps had smaller eyes than those from springs. This is consistent with the results of our laboratory rearing experiment, which indicated that animals raised in tea-stained water had slightly smaller eyes than those raised in clear water conditions. These two disparate patterns suggest that the determinants of eye size are currently unknown.

光照环境的差异会对视觉系统提出差异化需求，以保障在特定环境中成功检测并解读视觉信号。眼睛大小是视觉系统的核心属性，其对视觉敏度(visual acuity)与视觉敏感度(visual sensitivity)均存在显著影响。尽管已有诸多比较研究针对不同光照环境下的鱼类类群展开了眼大小分析——例如洞穴与地表生境、中层带与远洋带水深、浑浊与清澈水体——但针对种群间、物种内尺度下，水体透明度对眼大小差异的影响的相关研究仍较为匮乏。
本研究对比了佛罗里达州4条水系中，捕获于沼泽与泉水生境的野生个体的相对眼大小（即眼大小相对于标准体长的残差）。此外我们还开展了室内饲养实验，将实验对象饲养于模拟泉水与沼泽生境的清澈水体或茶色水体中，以探究光照条件驱动的表型可塑性(phenotypic plasticity)是否会对相对眼大小产生影响。
野外捕获个体的相对眼大小在种群间存在显著差异，但并未与光照环境呈现明确关联。南部种群（沼泽生境较为常见）的个体相对眼大小大于北部种群（泉水生境较为常见）。
然而在佛罗里达州北部，来自沼泽的蓝鳍鳉(bluefin killifish)的相对眼大小较泉水生境的个体更小。这一结果与室内饲养实验的结论相符：饲养于茶色水体中的个体相对眼大小略小于饲养于清澈水体中的个体。
上述两种截然不同的观测模式表明，当前我们仍未明确鱼类眼大小的决定因素。