[Functional characteristics of electroreceptors (small pitted organs) of the dwarf catfish]

The response characteristics of the small pit organs in the catfish Ictalurus nebulosus to electrical stimuli of various polarities, intensities and durations were investigated using the recording of electrical activity from single nerve fibres of the lateral nerve. The fibres showed background activity either rhythmical (35-45 imp/s) or modulated by fish swimming movements. The current density thresholds were in a range of 10 minus 10 -10 minus 11 /mm-2. Electrical stimulation evoked a phasic-tonic response in the electroreceptor fibres. The latencies varied from 10 to 50 ms for on-responses and from 10 to 200 ms for off-responses. Certain units responded with excitation to strong cathodal stimulation, and with excitatory response to anodal stimulus of weak or moderate intensity. The properties of small pit organs and other electroreceptors are compared.