A new electroreceptive teleost: Xenomystus nigri (Osteoglossiformes: Notopteridae)

Abstract

The African knife fish, Xenomystus nigri , is found to be sensitive to weak electric fields by the method of averaged evoked potentials from the brain. Slow waves and spikes were recorded in or near the lateral line area of the medulla and the torus semicircularis of the mesencephalon in response to long pulses (best > 50 ms) and low frequency sine waves (best ca. 10 Hz) of voltage gradients down to < 10 μV/cm. Evoked waves in the lateral line area are a sequence of negative and positive deflections beginning with a first peak at ca. 24 ms; in the torus semicircularis the first peak is at ca. 37 ms. Spikes are most likely in the torus between 50 and 80 ms after ON. At each recording locus there is a best axis of the homogeneous electric field and a better polarity. Effects of stimulus intensity, duration and repetition are described. The physiological properties are similar to those of ampullary receptor systems in mormyriforms, gymnotiforms and siluriforms.