ENVIRONMENTAL CONTROL OF RHYTHMIC BEHAVIOR IN THE WEAK-ELECTRIC FISH, GNATHONEMUS PETERSII (MORMYRIDAE) (BIOLOGICAL RHYTHMS, NOCTURNAL RHYTHMS, DIURNAL)

Rhythmic behavior of African weak-electric mormyrid fish is effected by light-dark cycles, temperature cycles and social contact. The present research was an analysis of these cues as potential zeitgebes for electric organ discharge rate and general locomotor activity rhythms in the mormyrid, Gnathonemus petersii. The fish's responses are discussed in the context of underlying oscillator systems.;Social contact synchronizes rhythms in many animals including fish, birds, rodents, and primates. Social communication in G. petersii is primarily mediated through the electrosensory system. It is difficult to record electric organ discharges from individuals within a group. Therefore an expeiment was designed that permitted only electrical contact between two fish. One fish was kept in constant darkness and its partner was entrained to a light-dark cycle. Only the arhythmic locomtor activity of the fish in constant darkness became rhythmic after electrical contact was established. The electric organ discharges of this fish did not entrain. Considering the interrelations between the activities of the two fish, minima and maxima in locomotor activity of the fish in constant darkness matched those of its entrained partner's locomotor activity and electric organ discharge activity. This suggested that locomotor activity entrained to cues from the electric organ discharge pattern of the entrained partner.;A light-dark cycle (LD 12:12) entrained both locomotor activity and electric organ discharge rate. A phase shift (6-hour delay) of the light-dark cycle produced a 6-hour phase shift of both activities. Under constant dark conditions (0.7 or 0.09 lux) both electric organ discharge rate and locomotor activity became arhythmic. Locomotor activity and electric organ discharge rhythms exhibited inter- and intra-individual variability in response to the imposed light regimens. A temperature cycle (warm:cool = 12 hr:12 hr, (DELTA)t = 5(DEGREES)) was ineffective as an entraining cue for locomotor activity.