Agonistic behavior of the weakly electric fish, Gnathonemus petersii (Mormyridae, Osteoglossomorpha).

The role played by the electric organ discharge (EOD) in eliciting and maintaining social behavior was assessed. First, a description of the motor acts associated with agonistic encounters between resident and intruder Gnathonemus petersii was provided: The temporal distribution of these acts depended on the aggressiveness of the resident. Second, half of the residents and half of the intruders were rendered electrically "silent" by cutting the nerves to the electric organ. Encounters were staged between pairs of intact fish, pairs of silent fish, and pairs in which one fish was intact and the other silent. Silent residents chased and attacked their opponents less often than the intact fish. Silent and intact residents did not differ in their rates of social probing. Intact intruders elicited higher rates of social probing, and the silent animals elicited more attacks. The effects of the fish's ability to emit EODs and perceive conspecific discharges on different motor acts are discussed.