Evidence of circadian rhythm of electric discharge in Eigenmannia virescens system

The gymnotid electric fish, Eigenmannia virescens, exhibits electric discha rge rhythmicity both in alternate light-dark (LD; 12h light, 12h dark [LD 1 2:12]) and in constant dark (DD) conditions. It suggests that the electric discharge rhythm is under control of the circadian clock. The free-running periods (FRPs) of electric discharge rhythms at 21 degrees C in DD are grea ter than, but close to, 24h. The maximum of the electric discharge in the E igenmannia system peaks approximately at circadian time 6 (CT6) in the midd le of the subjective day. The circadian oscillator in the system is tempera ture compensated. This original report reveals the relationship between ele ctric discharge activity and the circadian pacemaker in Eigenmannia and pro vides an alternative system to investigate circadian rhythms in vertebrates .