Cardiorespiratory responses to hypoxia in the African catfish, Clarias gariepinus (Burchell 1822), an air-breathing fish

J Comp Physiol B. 2011 Oct;181(7):905-16. doi: 10.1007/s00360-011-0577-z. Epub 2011 Apr 22.


The African catfish, Clarias gariepinus, possesses a pair of suprabranchial chambers located in the dorsal-posterior part of the branchial cavity having extensions from the upper parts of the second and fourth gill arches, forming the arborescent organs. This structure is an air-breathing organ (ABO) and allows aerial breathing (AB). We evaluated its cardiorespiratory responses to aquatic hypoxia. To determine the mode of air-breathing (obligate or accessory), fish had the respiratory frequency (f (R)) monitored and were subjected to normoxic water (PwO(2) = 140 mmHg) without becoming hyperactive for 30 h. During this period, all fish survived without displaying evidences of hyperactivity and maintained unchanged f (R), confirming that this species is a facultative air-breather. Its aquatic O(2) uptake ([Formula: see text]) was maintained constant down to a critical PO(2) (PcO(2)) of 60 mmHg, below which [Formula: see text] declined linearly with further reductions of inspired O(2) tension (PiO(2)). Just above the PcO(2) the ventilatory tidal volume (V (T)) increased significantly along with gill ventilation ([Formula: see text]), while f (R) changed little. Consequently, the water convection requirement [Formula: see text] increased steeply. This threshold applied to a cardiac response that included reflex bradycardia. AB was initiated at PiO(2) = 140 mmHg (normoxia) and air-breathing episodes increased linearly with more severe hypoxia, being significantly higher at PiO(2) tensions below the PcO(2). Air-breathing episodes were accompanied by bradycardia pre air-breath, to tachycardia post air-breath.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Air
  • Animals
  • Catfishes*
  • Fish Diseases / metabolism*
  • Fish Diseases / pathology
  • Gills / physiology
  • Heart / physiology*
  • Heart Rate / physiology
  • Hypoxia / metabolism
  • Hypoxia / pathology
  • Hypoxia / veterinary*
  • Oxygen Consumption
  • Pulmonary Ventilation / physiology
  • Respiration
  • Respiratory Mechanics*
  • Time Factors