Air breathing and aquatic gas exchange during hypoxia in armoured catfish

作者：Scott Graham R^*; Matey Victoria; Mendoza Julie Anne; Gilmour Kathleen M; Perry Steve F; Almeida Val Vera M F; Val Adalberto L

来源：Journal of Comparative Physiology B-Biochemical Systems and Environmental Physiology, 2017, 187(1): 117-133.

DOI：10.1007/s00360-016-1024-y

• Gas exchange
• Gill
• Ventilation
• Haemoglobin
• Myoglobin
• Calophysus macropterus
• Teleost

Air breathing in fish is commonly believed to have arisen as an adaptation to aquatic hypoxia. The effectiveness of air breathing for tissue O-2 supply depends on the ability to avoid O-2 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 O-2 loss while air breathing in aquatic hypoxia, and we measured various other respiratory and metabolic traits important for O-2 supply and utilization. Fish were instrumented with opercular catheters to measure the O-2 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 O-2 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 O-2 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-O-2 binding affinity when sampled in normoxia (P-50 of 3.1 kPa at pH 7.4), but were able to rapidly increase binding affinity during progressive hypoxia exposure (to a P-50 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 O-2 loss in armoured catfish while air breathing in aquatic hypoxia.

• 出版日期2017-1