Department of Integrative Biology, University of Guelph, 50 Stone Road East, Guelph, Ontario, Canada N1G 2W1.
Proc Biol Sci. 2020 Feb 12;287(1920):20192796. doi: 10.1098/rspb.2019.2796.
The morphology of fish gills is closely linked to aerobic capacity and tolerance of environmental stressors such as hypoxia. The importance of gill surface area is well studied, but little is known about how the mechanical properties of gill tissues determine function. In some fishes, the bases of the gill filaments are surrounded by a calcified 'sheath' of unknown function. We tested two non-exclusive hypotheses: (i) calcified gill filaments enhance water flow through the gill basket, improving aquatic respiratory function, and (ii) in amphibious fishes, calcification provides support for gills out of water. In a survey of more than 100 species of killifishes and related orders, we found filament calcification was widespread and thus probably arose before the evolution of amphibious lifestyles in killifishes. Calcification also did not differ between amphibious and fully aquatic species, but terrestrial acclimation caused calcium deposition on the filaments of the killifish , suggesting a possible structural role when out of water. We found strong evidence supporting a role for filament calcification in enhancing aquatic respiratory function. First, acclimation to increased respiratory demands (hypoxia, elevated temperatures) induced calcium deposition on the filaments of . Next, gentle removal of filament calcification decreased branchial resistance to water flow, indicating disruption of gill basket positioning. Thus, the mechanical properties of the gill filaments appear to play an important and previously unappreciated role in determining fish respiratory function.
鱼类鳃的形态与有氧能力和对环境胁迫（如缺氧）的耐受性密切相关。鳃表面积的重要性已经得到了充分的研究，但对于鳃组织的机械性能如何决定其功能，我们知之甚少。在一些鱼类中，鳃丝的基部被一层未知功能的钙化“鞘”所包围。我们检验了两个非排他性的假说：（i）钙化的鳃丝增强了水通过鳃篮的流动，从而改善了水生呼吸功能；（ii）在两栖鱼类中，钙化为离开水的鳃提供了支撑。在对超过 100 种的食蚊鱼和相关目鱼类的调查中，我们发现鳃丝钙化非常普遍，因此可能是在食蚊鱼的两栖生活方式进化之前就出现了。钙化在两栖和完全水生物种之间也没有差异，但在陆地上适应会导致食蚊鱼鳃丝上的钙沉积，这表明在离开水时可能具有结构作用。我们发现了有力的证据支持鳃丝钙化在增强水生呼吸功能方面的作用。首先，对呼吸需求增加（缺氧、高温）的适应会导致钙沉积在鳃丝上。其次，温和地去除鳃丝钙化会降低鳃对水流的阻力，这表明鳃篮的位置发生了混乱。因此，鳃丝的机械性能似乎在决定鱼类呼吸功能方面发挥了重要而以前未被重视的作用。
