title: Cardiorespiratory responses to hypoxia in the African catfish, Clarias gariepinus (Burchell 1822), an air-breathing fish.
abstract: 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.
authors.affiliation: Department of Physiological Sciences, Federal University of São Carlos (UFSCar), Via Washington Luiz, km 235, 13565-905, São Carlos, SP, Brazil.
authors.forename: T C
authors.initials: TC
authors.lastname: Belão
authors.forename: C A C
authors.initials: CA
authors.lastname: Leite
authors.forename: L H
authors.initials: LH
authors.lastname: Florindo
authors.forename: A L
authors.initials: AL
authors.lastname: Kalinin
authors.forename: F T
authors.initials: FT
authors.lastname: Rantin
mesh_terms: D000388:Air; D000818:Animals; D002397:Catfishes; D005393:Fish Diseases / Q000378:metabolism* / Q000473:pathology; D005880:Gills / Q000502:physiology; D006321:Heart / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D000860:Hypoxia / Q000378:metabolism / Q000473:pathology / Q000662:veterinary*; D010101:Oxygen Consumption; D012123:Pulmonary Ventilation / Q000502:physiology; D012119:Respiration; D015656:Respiratory Mechanics; D013997:Time Factors