Flight-Associated Discharge Pattern in a Weakly Electric Fish, Gnathonemus Petersii (Mormyridae, Teleostei)

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Abstract
A GnathonEmus petersii which is put into the tank of a Mormyrus rume, or of an electrically silenced G. petersii, displays a discharge rate which is only one fourth (8 Hz) the rate exhibited by an attacking, territory-defending animal. In both instances, the variability of intervals is great. In contrast to the bimodal histogram of an attacking animal, the histogram of an inferior, fleeing fish displays only one mode. This mode is identical to the burst activity-mode of the resting histogram, and different from the swimming histogram mode. So the histogram displayed by an attacked and persecuted animal is significantly different from the histograms exhibited by i) isolated resting, ii) isolated swimming, and iii) attacking fish. During an attack-elicited escape reaction, G. petersii increases its discharge rate up to 55 Hz in a step-like fashion, while regularising the length of successive intervals ("fleeing signal"). The step-like discharge rate increase is also shown by the receiver of an Approach who does not move. This suggests that the step-like discharge rate increase, associated with the escape reaction, is not an incidental response to changed motor activity. The "fleeing signal" presumably is i) an incidental response to a vegetative reaction, or ii) it may have the significance of a signal communicating a socially relevant message (e.g. threat). A GnathonEmus petersii which is put into the tank of a Mormyrus rume, or of an electrically silenced G. petersii, displays a discharge rate which is only one fourth (8 Hz) the rate exhibited by an attacking, territory-defending animal. In both instances, the variability of intervals is great. In contrast to the bimodal histogram of an attacking animal, the histogram of an inferior, fleeing fish displays only one mode. This mode is identical to the burst activity-mode of the resting histogram, and different from the swimming histogram mode. So the histogram displayed by an attacked and persecuted animal is significantly different from the histograms exhibited by i) isolated resting, ii) isolated swimming, and iii) attacking fish. During an attack-elicited escape reaction, G. petersii increases its discharge rate up to 55 Hz in a step-like fashion, while regularising the length of successive intervals ("fleeing signal"). The step-like discharge rate increase is also shown by the receiver of an Approach who does not move. This suggests that the step-like discharge rate increase, associated with the escape reaction, is not an incidental response to changed motor activity. The "fleeing signal" presumably is i) an incidental response to a vegetative reaction, or ii) it may have the significance of a signal communicating a socially relevant message (e.g. threat).

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