TEMPORAL STRUCTURE IN STICKLEBACK BEHAVIOR

Research was started into a possible circadian periodicity in the beha viour of the three-spined stickleback. The behaviour of solitary males in the sexual phase of their breeding cycle was studied under constan t conditions, including illumination of constant brightness (LL). No,' free-running', circadian rhythm was found. Both the frequency of nest- visits and the rate of creeping-through (which shows an ultradian peri odicity) were remarkably constant over long periods. Also, operant con ditioning experiments, in which the male could switch the lights on or off, did not reveal any circadian fluctuation in the preference for l ight or dark. In the course of the long-term recordings 'rest-periods' were found, lasting some 10 to 50 minutes, in which the fish was surp risingly inactive, and did not visit the nest. Although some character istics of these 'rest-periods' seem to point to a 'sleep-like' nature, others seem to argue against this.