A Noninvasive Electrophysiological Investigation of Tactile Sensitivity in Cyprinid Fish (Cyprinidae).

Tactile reception in cyprinid fish (silver crucian carp Carassius auratus gibelio and common carp Cyprinus carpio) was investigated by noninvasive recording of action potentials from the head skin in response to rhythmic tactile stimulation. Responses shaped as electric potentials following synchronously with changes in the pressure force on the skin were recorded using chloro-silver electrodes. It was shown that fish, like all terrestrial vertebrates, have phasic and tonic tactile receptors. Three main types of tactile responses were distinguished: (1) tonic responses as potential fluctuations repeating the dynamics of the tactile stimulus, (2) phasic responses as on-, off-, and on-off potentials, and (3) slow deflections from the resting potential. Compound responses comprising simultaneously different types of responses were also recorded. The response latency averaging 6.1 ms for tonic and 4.4 ms for phasic responses was clearly independent of the stimulus direction (switch-on, switch-off). The threshold level of tactile sensitivity in the perioral and gular head areas was 0.05–0.2 g/mm2. Tactile receptors on the silver crucian carp and common carp heads exhibited zonal distribution patterns, with sensory areas differing in their tactile sensitivity. Most sensitive areas were on the upper and lower lips, in the perilabial skin and the gular area on the ventral side of the head. Less sensitive areas were situated rostrally and ventrally to the eyeball. The areas situated dorsally and caudally to the eyeball proved to be insensitive to the applied tactile stimulation. In all sensory areas on the fish head, most intense responses were evoked by sliding tactile stimuli. The distribution specificity of tactile sensory areas meets their functional significance for fish feeding behavior. [ABSTRACT FROM AUTHOR]