Abstract：
We present the first description of inspiration-first air breaths in royal knifefish, Chitala blanci, a ray-finned fish known to use four-stroke air breaths. Four-stroke breaths are used by nearly all ray-finned fish species that use their gas bladder to breathe air and are the ancestral breath type of ray-finned fishes. Interestingly, one such species, Amia calva, is known to perform two distinct breath types. Amia use four-stroke breaths when they need more oxygen and performs inspiration-first breaths to restore buoyancy. We observed that C. blanci also performs inspiration-first breaths and tested whether the two breath types are performed for the same functions in C. blanci as they are in Amia. We recorded the frequency of each breath type when exposed to aquatic hypoxia and two conditions of oxygen availability. We found that C. blanci performed more four-stroke breaths (81% ± 15% of total breaths) than inspiration-first breaths when exposed to aerial normoxia but performed more inspiration-first breaths (72% ± 40%) than four-stroke breaths when exposed to aerial hyperoxia. These patterns match those described for Amia and indicate that C. blanci performs four-stroke breaths in response to oxygen depletion and performs inspiration-first breaths to maintain buoyancy. Few studies have examined the role of air-breathing in buoyancy regulation. Decreasing buoyancy, rather than oxygen availability, to stimulate air breaths may reveal that inspiration-first breaths are more common among fishes than we are aware. We consider this possibility and present a new hypothesis for the origin and early evolution of air breathing in vertebrates.
摘要：
我们首先描述了皇家刀鱼的灵感第一空气呼吸，ChitalaBlanci,一种鱼鳍鱼，已知使用四冲程空气呼吸。几乎所有射线鳍鱼类都使用四冲程呼吸，它们使用气囊呼吸空气，并且是射线鳍鱼类的祖先呼吸类型。有趣的是,一个这样的物种，AmiaCalva,已知执行两种不同的呼吸类型。Amia在需要更多氧气时使用四冲程呼吸，并进行吸气先呼吸以恢复浮力。我们观察到C.blanci也执行吸气优先呼吸，并测试了两种呼吸类型是否在C.blanci中执行与Amia相同的功能。我们记录了暴露于水生缺氧和两种氧气可用性条件下每种呼吸类型的频率。我们发现，C.blanci在暴露于空中常氧时进行的四冲程呼吸（占总呼吸的81％±15％）比吸气第一呼吸多，但在暴露于空中高氧时进行的吸气第一呼吸（72％±40％）比四冲程呼吸多。这些模式匹配Amia所描述的模式，表明C.blanci响应于氧气消耗而进行四冲程呼吸，并进行吸气优先呼吸以保持浮力。很少有研究研究空气呼吸在浮力调节中的作用。降低浮力，而不是氧气的可用性，刺激空气呼吸可能表明，灵感优先呼吸在鱼类中比我们所知的更常见。我们考虑了这种可能性，并为脊椎动物呼吸空气的起源和早期演变提出了新的假设。
