Miscellaneous features of electroreceptors in Gnathonemus petersii (Gunther, 1862) (Pisces, Teleostei, Mormyriformes)

The cutaneous electrical activity of ampullary and tuberous electroreceptor organs of Gnathonemus petersii (Teleostei, Mormyriformes) was studied in seven specimens. The spontaneous activity levels of 38 ampullary primary afferents showed significant differences between individual fishes rather than between different loci within a single specimen. Spontaneous activity of ampullary electroreceptor organs is not constant, but depends on some unknown factor, e.g. occlusion of the ampullary opening or local accumulation of ions. Both under Saffan and Hypnodil anesthesia it proved possible to record ampullary primary afferent activity from anesthetized specimens. Ampullary organ activity is modulated by Electric Organ Discharges and by respiratory potentials. Respiratory potentials also modulate the cutaneous electrical activity of mormyromasts. The ion composition of the water influences the cutaneous electrical oscillations of the Knollen organs.