Division of Zoophysiology, Department of Biology, Aarhus University, 8000C Aarhus, Denmark.
Department of Biological Sciences, University of North Texas, 1155 Union Circle, Denton, TX 76203, USA.
Proc Biol Sci. 2023 Sep 13;290(2006):20231353. doi: 10.1098/rspb.2023.1353.
In hypoxia, air-breathing fish obtain O from the air but continue to excrete CO into the water. Consequently, it is believed that some O obtained by air-breathing is lost at the gills in hypoxic water. is an air-breathing catfish with very large gills from the Mekong River basin where it is cultured in hypoxic ponds. To understand how can maintain high growth in hypoxia with the presumed O loss, we quantified respiratory gas exchange in air and water. In severe hypoxia (PO: ≈ 1.5 mmHg), it lost a mere 4.9% of its aerial O uptake, while maintaining aquatic CO excretion at 91% of the total. Further, even small elevations in water PO rapidly reduced this minor loss. Charting the cardiovascular bauplan across the branchial basket showed four ventral aortas leaving the bulbus arteriosus, with the first and second gill arches draining into the dorsal aorta while the third and fourth gill arches drain into the coeliacomesenteric artery supplying the gut and the highly trabeculated respiratory swim-bladder. Substantial flow changes across these two arterial systems from normoxic to hypoxic water were not found. We conclude that the proposed branchial oxygen loss in air-breathing fish is likely only a minor inefficiency.
在缺氧环境中，空气呼吸鱼类从空气中获取氧气，但仍将二氧化碳排泄到水中。因此，人们认为，一些通过空气呼吸获得的氧气会在缺氧水中从鳃部损失掉。湄公河流域有一种具有非常大鳃的空气呼吸鲶鱼，它在缺氧池塘中养殖。为了了解空气呼吸的如何在氧气损失的情况下在缺氧环境中保持高生长，我们量化了在空气和水中的呼吸气体交换。在严重缺氧（PO：≈1.5mmHg）下，它仅损失了其空气中氧气摄取量的 4.9%，同时保持了 91%的水中二氧化碳排泄量。此外，即使水中 PO 的微小升高也会迅速减少这种少量的损失。绘制横跨鳃篮的心血管结构蓝图显示，有四条腹主动脉从动脉球离开，第一和第二鳃弓排入背主动脉，而第三和第四鳃弓排入供应肠道和高度小梁化呼吸鳔的腹腔肠系膜动脉。从正常氧合水到缺氧水，这些两个动脉系统的流量变化不大。我们得出结论，空气呼吸鱼类中提出的鳃部氧气损失可能只是一个较小的效率低下。
