GuppiesPoecilia reticulata(Peters) were subjected to repeated measures of 5 min duration, on an open field test. The major measures were the number of times a fish changed sections, the number of different sections entered regardless of how many times they entered a section and the ratio of inner to outer sections entered. The activity scores were on a continuous distribution from fish to fish and for the males correlated highly with the ratio of inner to outer movements, but not so for the females. All fish showed a preference for the outer rings compared to the inner rings. There was a non–significant tendency for the male activity to increase during each test, but to wane as the number of tests increased. The females showed a variation of activity which may be associated with their ovarian cycle, but the various activity measures tended not to correlate with each other during the cycle and also failed to correlate with various published cycles of physiological ovarian activit