Glucocorticoid receptor blockade inhibits brain cell addition and aggressive signaling in electric fish, Apteronotus leptorhynchus

► Electric fish living in pairs produced chirps at high rates. ► Treating paired fish with glucocorticoid receptor blocker, RU486, decreased chirp rate. ► RU486 treatment had no effect on EOD frequency or locomotion. ► RU486 decreased cell addition to the periventricular zone. ► The effect of RU486 on cell addition was partial.