Air breathing and aquatic gas exchange during hypoxia in armoured catfish

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• 作者：Graham R. Scott ; Victoria Matey ; Julie-Anne Mendoza…
• 关键词：Gas exchange ; Gill ; Ventilation ; Haemoglobin ; Myoglobin ; Calophysus macropterus ; Teleost
• 刊名：Journal of Comparative Physiology B
• 出版年：2017
• 出版时间：January 2017
• 年：2017
• 卷：187
• 期：1
• 页码：117-133
• 全文大小：
• 刊物类别：Biomedical and Life Sciences
• 刊物主题：Animal Physiology; Biomedicine, general; Human Physiology; Zoology; Biochemistry, general;
• 出版者：Springer Berlin Heidelberg
• ISSN：1432-136X
• 卷排序：187

文摘

Air breathing in fish is commonly believed to have arisen as an adaptation to aquatic hypoxia. The effectiveness of air breathing for tissue O₂ supply depends on the ability to avoid O₂ loss as oxygenated blood from the air-breathing organ passes through the gills. Here, we evaluated whether the armoured catfish (Hypostomus aff. pyreneusi)—a facultative air breather—can avoid branchial O₂ loss while air breathing in aquatic hypoxia, and we measured various other respiratory and metabolic traits important for O₂ supply and utilization. Fish were instrumented with opercular catheters to measure the O₂ tension (PO₂) of expired water, and air breathing and aquatic respiration were measured during progressive stepwise hypoxia in the water. Armoured catfish exhibited relatively low rates of O₂ consumption and gill ventilation, and gill ventilation increased in hypoxia due primarily to increases in ventilatory stroke volume. Armoured catfish began air breathing at a water PO₂ of 2.5 kPa, and both air-breathing frequency and hypoxia tolerance (as reflected by PO₂ at loss of equilibrium, LOE) was greater in individuals with a larger body mass. Branchial O₂ loss, as reflected by higher PO₂ in expired than in inspired water, was observed in a minority (4/11) of individuals as water PO₂ approached that at LOE. Armoured catfish also exhibited a gill morphology characterized by short filaments bearing short fused lamellae, large interlamellar cell masses, low surface area, and a thick epithelium that increased water-to-blood diffusion distance. Armoured catfish had a relatively low blood-O₂ binding affinity when sampled in normoxia (P₅₀ of 3.1 kPa at pH 7.4), but were able to rapidly increase binding affinity during progressive hypoxia exposure (to a P₅₀ of 1.8 kPa). Armoured catfish also had low activities of several metabolic enzymes in white muscle, liver, and brain. Therefore, low rates of metabolism and gill ventilation, and a reduction in branchial gas-exchange capacity, may help minimize branchial O₂ loss in armoured catfish while air breathing in aquatic hypoxia.