Communication and Waveform Analysis in Weakly Electric Fishes With Special Emphasis on Mormyrids

The electric sense in fishes was discovered in the 1950s. African snoutfish (Mormyridae) and South American knifefishes (Gymnotiformes) generate electric fields for testing their environment by Active Electrolocation, and for communication. These fishes’ electric organ discharges (EODs) are species-specific (or –characteristic) pulses or continuous waves, and vary widely in waveform, duration (frequency) and strength. In mormyrids the sequence (or pattern) of pulse intervals carries motivational and species-specific information. In a natural hybrid species complex, choosy females of the parent species block a speciation reversal by their preference for conspecific EOD waveforms, and rejection of the hybrid form. Electrosensory discrimination thresholds appear adapted to the fine detail of the EOD pulse waveforms on a ms-scale, with spectral cues not required in Pollimyrus adspersus. In some mormyrid species, breeding males add a strong D.C. component to their EOD, which attracts females but also low-frequency sensitive catfish predators. In several species, specific EOD patterns, as well as loud vocalizing, accompany courtship and spawning. The larvaes’ early EODs of long pulse duration and initially low rate is replaced by an adult short EOD in young juveniles; parental care is present in Pollimyrus species. Three syntopic species gave examples of conflictual and cooperative electrocommunication in a semi-natural environment. Eigenmannia, a wave gymnotiform fish, is highly phase sensitive to stimuli of 0 Hz frequency difference, which evoke a Jamming Avoidance Response (which is a frequency shift away from the stimulus). The strength of the JAR depends on the phase difference stimulus to EOD. At a sufficient frequency difference, trained, food-rewarded Eigenmannia discriminate waveforms by a temporal mechanism that does not require spectral cues. Eigenmannia is incapable of discriminating stimuli that are phase-locked at maintained frequency identity.