A new hypothesis on the air flow in air breathing in Clarias gariepinus (Teleostei: Siluriformes).

Clarias gariepinus (BURCHELL, 1822) breathes air at the surface. Aerial breathing requires a flow of air through intercommunicating cavities (buccopharyngeal cavity, opercular and suprabranchial cavities). Cinematographic observations on normal and abnormal catfishes lead to a new hypothesis about air-breathing in Clarias. 1) At rest on the bottom, the suprabranchial cavity is filled with air. 2) While coming up to the surface, a part of the air of the suprabranchial cavity passes to the opercular cavities, especially in their anterior part, through slits between the fan-like valves borne on the epibranchials. 3) Somewhat later, opercular adduction results in expulsion of bubbles through the opercular slits. 4) When the snout reaches the surface, the mouth is wide open. Depression of the hyoid bars and opercular abduction produce aspiration of air into the buccopharyngeal cavity. 5) Air is forced into the suprabranchial cavity, through the third branchial slit by mouth closure and buccopharyngeal constriction. Hyoid bars elevation plays a prominent role in that constriction as demonstrated by the partial impossibility for abnormal Clarias with locked hyoid bars to push air from the mouth to the suprabranchial cavities.