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Research article2021Peer reviewed

Striped catfish (Pangasianodon hypophthalmus) use air-breathing and aquatic surface respiration when exposed to severe aquatic hypercarbia

Morgan, Rachael; Tunnah, Louise; Tuong, Dang D.; Hjelmstedt, Per; Nhu, Pham N.; Stiller, Kevin T.; Phuong, Nguyen Thanh; Huong, Do Thi Thanh; Bayley, Mark; Wang, Tobias; Milsom, William K.


We investigated the extent to which the facultative air-breathing fish, the striped catfish (Pangasianodon hypophthalmus), uses air-breathing to cope with aquatic hypercarbia, and how air-breathing is influenced by the experimental exposure protocol and level of hypercarbia. We exposed individuals to severe aquatic hypercarbia (up to PwCO2 = 81 mmHg) using step-wise and progressive exposure protocols while measuring gill ventilation rate, heart rate, mean arterial blood pressure, and air-breathing frequency, as well as arterial blood pH and PCO2. We confirm that P. hypophthalmus is tolerant of hypercarbia. Under both protocols gill ventilation rate, heart rate, and mean arterial blood pressure were maintained near control levels even at very high CO2 levels. We observed a marked amount of individual variation in the PwCO(2) at which air-breathing was elicited, with some individuals not responding at all. The experimental protocol also influenced the onset of air-breathing. Air-breathing began at lower PwCO2 in the step-wise protocol (23 +/- 4.1 mmHg) compared with the progressive protocol (46 +/- 7.8 mmHg). Air-breathing was often followed by aquatic surface respiration, at higher PCO2 (71 +/- 5.2 mmHg) levels. On average, the blood PCO2 was approximately 43% lower (46 +/- 2.5 mmHg) than water PwCO2 (similar to 81 mmHg) at our highest tested CO2 level. While this suggests that aerial CO2 elimination is an effective, and perhaps critical, respiratory strategy used by P. hypophthalmus to cope with severe hypercarbia, this observation may also be explained by a long lag time required for equilibration.


aerial respiration; blood gases; cardiorespiratory control; CO2; hypercapnia; Pangasius

Published in

Journal Of Experimental Zoology Part A:Ecological And Integrative Physiology
2021, Volume: 335, number: 9-10, pages: 820-830
Publisher: WILEY