On the Interactions Between Suctorial Adhesion, Gill Ventilation and Opercular Spine Erection In Xenocara Occidentalis*

1. Except for brief swimming from one site of adhesion to another, the oral sucker of Xenocara is constantly used to anchor the fish to the substratum. 2. During adhesion oral inhalation is by rhythmic water flow through special grooves in the sucker wall. Coarse particles entering with the respiratory water elicit a cough-like response which is associated with large positive pressures in the buccopharynx and opercular cavities, and with enhancement of suctorial adhesion. 3. Stronger adhesion occurs when the fish responds to tactile stimulation, during which large negative pressures are developed throughout the respiratory system and the opercular spines are thrust outward. 4. In all responses separation of suctorial and respiratory function is facilitated by the action of a muscular oral valve. Precise co-ordination between the inlet valves of the maxillary barbels and the oral and opercular valves is important for efficiency of the suction and force pumps before the gills and the opercular suction pump behind them.