Journal of Comparative Physiology B

, Volume 188, Issue 4, pp 581–589 | Cite as

Ventilatory responses of the clown knifefish, Chitala ornata, to hypercarbia and hypercapnia

  • Dang Diem Tuong
  • Brittney Borowiec
  • Alexander M. Clifford
  • Renato Filogonio
  • Derek Somo
  • Do Thi Thanh Huong
  • Nguyen Thanh Phuong
  • Tobias Wang
  • Mark Bayley
  • William K. MilsomEmail author
Original Paper


The aim of the present study was to determine the roles of externally versus internally oriented CO2/H+-sensitive chemoreceptors in promoting cardiorespiratory responses to environmental hypercarbia in the facultative air-breathing fish, Chitala ornata (the clown knifefish). Fish were exposed to environmental acidosis (pH ~ 6.0) or hypercarbia (≈ 30 torr PCO2) that produced changes in water pH equal to the pH levels of the acidotic water to distinguish the relative roles of CO2 versus H+. We also injected acetazolamide to elevate arterial levels of PCO2 and [H+] in fish in normocarbic water to distinguish between internal and external stimuli. We measured changes in gill ventilation frequency, air breathing frequency, heart rate and arterial blood pressure in response to each treatment as well as the changes produced in arterial PCO2 and pH. Exposure to normocarbic water of pH 6.0 for 1 h did not produce significant changes in any measured variable. Exposure to hypercarbic water dramatically increased air breathing frequency, but had no effect on gill ventilation. Hypercarbia also produced a modest bradycardia and fall in arterial blood pressure. Injection of acetazolamide produced similar effects. Both hypercarbia and acetazolamide led to increases in arterial PCO2 and falls in arterial pH although the changes in arterial PCO2/pH were more modest following acetazolamide injection as were the increases in air breathing frequency. The acetazolamide results suggest that the stimulation of air breathing was due, at least in part, to stimulation of internally oriented CO2/H+ chemoreceptors monitoring blood gas changes.


Fish CO2 Gill ventilation Air breathing Acidosis Hypercarbia 



This research was funded by the Danish Ministry of Foreign Affairs: Danida fellowship Centre Project 272 number: DFC 12-014AU iAQUA, The Danish International Development Agency (DANIDA) and by the Natural Sciences and Engineering Research Council of Canada.


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  • Dang Diem Tuong
    • 1
  • Brittney Borowiec
    • 2
  • Alexander M. Clifford
    • 3
    • 5
  • Renato Filogonio
    • 4
  • Derek Somo
    • 5
  • Do Thi Thanh Huong
    • 1
  • Nguyen Thanh Phuong
    • 1
  • Tobias Wang
    • 6
    • 7
  • Mark Bayley
    • 6
  • William K. Milsom
    • 5
    Email author
  1. 1.Department of Aquatic Nutrition and Products Processing, College of Aquaculture and FisheriesCan Tho UniversityCan ThoVietnam
  2. 2.Department of BiologyMcMaster UniversityHamiltonCanada
  3. 3.Department of Biological SciencesUniversity of AlbertaEdmontonCanada
  4. 4.Department of Physiological SciencesUniversidade Federal de São CarlosSão CarlosBrazil
  5. 5.Department of ZoologyUniversity of British ColumbiaVancouverCanada
  6. 6.Department of Bioscience, ZoophysiologyAarhus UniversityAarhusDenmark
  7. 7.Aarhus Institute of Advanced StudiesAarhus CDenmark

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