Design features for electric communication

How do the communication discharges produced by electric fish evolve to acc ommodate the unique design features for the modality? Two design features a re considered: first, the limited range of signaling imposed on the electri c modality by the physics of signal transmission from dipole sources; and s econd, the absence of signal echoes and reverberations for electric dischar ges, which are non-propagating electrostatic fields. Electrostatic theory predicts that electric dicharges from fish will have a short range because of the inverse cube law of geometric spreading around an electrostatic dipole, From this, one predicts that the casts of signalin g will be high when fish attempt to signal over a large distance. Electric fish mag economize in signal production whenever possible. For example, som e gymnotiform fish appear to be impedance-matched to the resistivity of the water; others modulate the amplitude of their discharge seasonally and diu rnally. The fact that electric signals do not propagate, but exist as electrostatic fields, means that, unlike sound signals, electric organ discharges produc e no echoes or reverberations. Because temporal information is preserved du ring signal transmission, receivers may pay close attention to the temporal details of electric signals. iis a consequence, electric organs have evolv ed with mechanisms for controlling the fine structure of electric discharge waveforms.