title: High capacity for extracellular acid-base regulation in the air-breathing fish Pangasianodon hypophthalmus.
abstract: The evolution of accessory air-breathing structures is typically associated with reduction of the gills, although branchial ion transport remains pivotal for acid-base and ion regulation. Therefore, air-breathing fishes are believed to have a low capacity for extracellular pH regulation during a respiratory acidosis. In the present study, we investigated acid-base regulation during hypercapnia in the air-breathing fish Pangasianodon hypophthalmus in normoxic and hypoxic water at 28-30°C. Contrary to previous studies, we show that this air-breathing fish has a pronounced ability to regulate extracellular pH (pHe) during hypercapnia, with complete metabolic compensation of pHe within 72 h of exposure to hypoxic hypercapnia with CO2 levels above 34 mmHg. The high capacity for pHe regulation relies on a pronounced ability to increase levels of HCO3(-) in the plasma. Our study illustrates the diversity in the physiology of air-breathing fishes, such that generalizations across phylogenies may be difficult.
authors: Section for Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus, Denmark cdamsg@gmail.com.
authors: Christian
authors: C
authors: Damsgaard
authors: College of Aquaculture and Fisheries, Can Tho University, 92000 Can Tho City, Vietnam.
authors: Le Thi Hong
authors: le TH
authors: Gam
authors: College of Aquaculture and Fisheries, Can Tho University, 92000 Can Tho City, Vietnam.
authors: Dang Diem
authors: DD
authors: Tuong
authors: College of Aquaculture and Fisheries, Can Tho University, 92000 Can Tho City, Vietnam.
authors: Phan Vinh
authors: PV
authors: Thinh
authors: College of Aquaculture and Fisheries, Can Tho University, 92000 Can Tho City, Vietnam.
authors: Do Thi
authors: do T
authors: Huong Thanh
authors: Section for Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus, Denmark.
authors: Tobias
authors: T
authors: Wang
authors: Section for Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus, Denmark.
authors: Mark
authors: M
authors: Bayley
mesh_terms: D000136:Acid-Base Equilibrium; D000818:Animals; D002245:Carbon Dioxide / Q000097:blood*; D002397:Catfishes / Q000502:physiology*; D010100:Oxygen / Q000032:analysis; D045483:Rivers / Q000737:chemistry
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen
keywords: Carbon dioxide; Hypercapnia; Hypoxia; Pangasius