ENCLOSURE AND CONNECTION ELECTRICALLY DESIGNED FEATURES

Abstract

How do the communication discharges produced by electric fish evolve to accommodate the unique design
features for the modality? Two design features are considered: first, the limited range of signaling imposed on the electric
modality by the physics of signal transmission from dipole sources; and second, the absence of signal echoes and
reverberations for electric discharges, 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 costs of signaling will be high when fish attempt to signal
over a large distance. Electric fish may economize in signal production whenever possible. For example, some gymnotiform fish
appear to be impedance-matched to the resistivity of the water; others
modulate the amplitude of their discharge seasonally and diurnally.
The fact that electric signals do not propagate, but exist as electrostatic fields, means that, unlike sound signals, electric organ
discharges produce no echoes or reverberations. Because temporal information is preserved during signal transmission, receivers may
pay close attention to the temporal details of electric signals. As a consequence, electric organs have evolved with mechanisms for
controlling the fine structure of electric discharge waveforms.