Journal of Comparative Physiology B

, Volume 189, Issue 6, pp 673–683 | Cite as

Ventilatory responses of the clown knifefish, Chitala ornata, to arterial hypercapnia remain after gill denervation

  • Dang Diem TuongEmail author
  • Do Thi Thanh Huong
  • Nguyen Thanh Phuong
  • Mark Bayley
  • William K. Milsom
Original Paper


The aim of this study was to corroborate the presence of CO2/H+-sensitive arterial chemoreceptors involved in producing air-breathing responses to aquatic hypercarbia in the facultative air-breathing clown knifefish (Chitala ornata) and to explore their possible location. Progressively increasing levels of CO2 mixed with air were injected into the air-breathing organ (ABO) of one group of intact fish to elevate internal PCO2 and decrease blood pH. Another group of fish in which the gills were totally denervated was exposed to aquatic hypercarbia (pH ~ 6) or arterial hypercapnia in aquatic normocarbia (by injection of acetazolamide to increase arterial PCO2 and decrease blood pH). Air-breathing frequency, gill ventilation frequency, heart rate and arterial PCO2 and pH were recorded during all treatments. The CO2 injections into the ABO induced progressive increases in air-breathing frequency, but did not alter gill ventilation or heart rate. Exposure to both hypercarbia and acetazolamide post-denervation of the gills also produced significant air-breathing responses, but no changes in gill ventilation. While all treatments produced increases in arterial PCO2 and decreases in blood pH, the modest changes in arterial PCO2/pH in the acetazolamide treatment produced the greatest increases in air-breathing frequency. These results strengthen the evidence that internal CO2/H+ sensing is involved in the stimulation of air breathing in clown knifefish and suggest that it involves extra-branchial chemoreceptors possibly situated either centrally or in the air-breathing organ.


Air breathing CO2 Gill denervation Aquatic hypercarbia Acetazolamide 



This research was funded by the Danish Ministry of Foreign Affairs: Danida fellowship Centre Project 272 number: DFC 12-014 AU 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 2019

Authors and Affiliations

  1. 1.College of Aquaculture and FisheriesCan Tho UniversityCan ThoVietnam
  2. 2.Can Tho University Board of TrusteesCan Tho UniversityCan ThoVietnam
  3. 3.Department of Bioscience ZoophysiologyAarhus UniversityAarhusDenmark
  4. 4.Department of ZoologyUniversity of British ColumbiaVancouverCanada

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