Electrolocation-communication discharges of the fish Gymnotus carapo L. (Gymnotidae: Gymnotiformes) during behavioral sleep.

R.M Stopa,K Hoshino

doi:10.1590/s0100-879x1999001000008

Abstract

Technical problems have hampered the study of sleep in teleosts. The electrical discharges of Gymnotus carapo L. (Gymnotidae: Gymnotiformes) were monitored to evaluate their ease and reliability as parameters to study sleep. The discharges were detected by electrodes immersed in a glass aquarium and were recorded on a conventional polygraph. G. carapo showed conspicuous signs of behavioral sleep. During these periods, opercular beat rates were counted, electric discharges recorded, and the "sharp discharge increase" (SDI) of the orienting reflex was investigated. All 20 animals monitored maintained electrical discharges during behavioral sleep. The discharge frequencies during sleep (50.3 +/- 10.4 Hz) were not significantly different from those observed when the fish was awake and inactive (57.2 +/- 12.1 Hz) (Wilcoxon matched-pairs signed-ranks test, P>0.05). However, the SDI, which was prevalent in the awake fish, was not observed during periods of behavioral sleep. Additional observations showed that the species had cannibalistic habits. When presented with electrical discharges from a conspecific, the sleeping fish showed an initial decrease or pause in discharge frequency, while the awake fish did not have this response. We conclude that the electrical discharges of G. carapo were not conspicuous indicators of behavioral sleep. Discharges may have been maintained during sleep for sensory purposes, i.e., conspecific detection and avoidance of cannibalistic attacks.

Highlights

Recordings for the first 10 animals at 2325oC showed that inactive, awake fish emitted very regular pulse discharge frequencies ranging from 42 to 68 Hz (Figure 1)
Amplitude remained constant during sleep and waking periods if the fish did not change its position in the aquarium
To determine if electrical discharges occurred during sleep via mechanisms independent of those that control other aspects of sleep, behavior and electric organ discharges (EOD) were monitored in anesthetized fish

Summary

Introduction

Recordings for the first 10 animals at 2325oC showed that inactive, awake fish emitted very regular pulse discharge frequencies ranging from 42 to 68 Hz (mean ± SD of 53.5 ± 12.1 Hz) (Figure 1). EOD recordings unexpectedly showed that electrical discharges were maintained during behavioral sleep periods. To determine if electrical discharges occurred during sleep via mechanisms independent of those that control other aspects of sleep, behavior and EOD were monitored in anesthetized fish.

Results

Conclusion