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

• Published in: Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology Vol. 181; no. 7; pp. 905 - 916
• Main Authors: Belão, T. C., Leite, C. A. C., Florindo, L. H., Kalinin, A. L., Rantin, F. T.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.10.2011; Springer Nature B.V
• Subjects: Air; Animal Physiology; Animals; Biochemistry; Biomedical and Life Sciences; Biomedicine; Cardiac arrhythmia; Catfishes; Clarias gariepinus; Fish Diseases - metabolism; Fish Diseases - pathology; Gills - physiology; Heart - physiology; Heart Rate - physiology; Human Physiology; Hyperactivity; Hypoxia; Hypoxia - metabolism; Hypoxia - pathology; Hypoxia - veterinary; Life Sciences; Original Paper; Oxygen Consumption; Pulmonary Ventilation - physiology; Respiration; Respiratory Mechanics; Time Factors; Ventilation; Zoology; Brazil; Africa; Heart rate; Critical oxygen tension; Hypoxia; Oxygen uptake; Gill ventilation; Air-breathing
• ISSN: 0174-1578; 1432-136X
• DOI: 10.1007/s00360-011-0577-z

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 ( P wO 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 ( ) was maintained constant down to a critical P O 2 ( P cO 2 ) of 60 mmHg, below which declined linearly with further reductions of inspired O 2 tension ( P iO 2 ). Just above the P cO 2 the ventilatory tidal volume ( V T ) increased significantly along with gill ventilation ( ), while f R changed little. Consequently, the water convection requirement increased steeply. This threshold applied to a cardiac response that included reflex bradycardia. AB was initiated at P iO 2  = 140 mmHg (normoxia) and air-breathing episodes increased linearly with more severe hypoxia, being significantly higher at P iO 2 tensions below the P cO 2 . Air-breathing episodes were accompanied by bradycardia pre air-breath, to tachycardia post air-breath.