Communication by harmonization of electric organ discharge frequencies by Eigenmannia virescens (Sternopygidae, Pisces).

Spectrum analysis of the combined electric organ discharges of confined, interacting Eigenmannia virescens individuals indicated 1) the relative frequency position of each individual in the group's "chord" was invariably conserved, i.e. the fish do not cross each other in frequency; 2) the ratios of 2:3 and 3:4 between the frequencies of two individuals were conserved over intervals of many days; 3) changes in group size induced frequency shifts that were often quite dramatic. It is suggested that this "chord" may function in the communication of information regarding a group's spatial position and its social rank relations.