Electrolocation of objects in the electric fishEigenmannia (Rhamphichthyidae, Gymnotoidei)

Summary

The electric fish,Eigenmannia, is able to sense objects which differ in electrical conductivity from the surrounding water by detecting distortions of the current field associated with its electric organ discharges. While resting,Eigenmannia hovers near electrically-detectable objects and follows their motions. When such objects are swung in a sinusoidal manner, the fish follows with a certain gain and phase lag. This allows one to quantify performance in “electrolocation” in terms of gain and phase values as functions of frequency of object motion, object size and distance. As these parameters reach threshold values, the gain of the animal's Following Response approaches zero while its phase lag tends toward-π. Electrolocation deteriorates under “jamming” conditions, i.e. in the presence of electric signals with frequencies near the animal's discharge frequency.Eigenmannia prevents the deterioration of electrolocation by shifting its frequency away from noise frequencies.