Male and female electric fish produce characteristically different electric organ discharges (EOD).  Female Sternopygus pruduce EODs of shorter duration with higher frequencies.  Dunlap et al. (1997) determined that the duration and frequency of female EODs can be altered by administration of estrogen.  Their study shows that female Sternopygus that were treated with the higher doses of estrogen produced EODs of shorter duration and higher frequency than both female fish who were given lower doses of estrogen and those who were not administered estrogen.

Zakon (1996) demonstrated that administration of estrogen to either sex Sternopygus resulted in shortened duration and raised frequency EODs.  Administration of testosterone to either sex Sternopygus produced exactly the opposite effect of estrogen administration:  signal duration increased and signal frequency lowered.  Zakon also administered testosterone to both sexes of Apteronotus.  He found that females who rarely chirp (make rapid rises in EOD frequency) increased both the number and magnitude of chirps gradually following testosterone administration.

Apteronotus leptorhynchus photo by Galvis, G./Mojica, J.I./Camargo, M.