Mechanoreceptor activity in the gills of the carp. I. Gill filament and gill raker mechanoreceptors.

Physiological properties of gill filament and gill raker mechanoreceptors in the gills of spontaneously breathing carp, Cyprinus carpio L., were analysed. Stroking stimuli applied to gill filaments elicited a phasic mechanoreceptive response, which was recorded from neurons in the epibranchial ganglia. Sustained deflection resulted in a short on-off response. The same neurons were also activated by slight movements of lamellae on a gill filament. The receptive field extended over all the lamellae of one filament at most, but generally covered a small part of it, including both dorsal and ventral lamellae. Deflection of gill rakers also elicited a brief response in epibranchial ganglion neurons. The threshold of both filament-related and gill raker mechanoreceptors was relatively high. They did not respond during normal respiration. It was therefore argued that these receptors do not function in normal respiratory control, but rather serve against mechanical damage from excessive pressure or particles in the water.