The relationship between maturation stage and movement pattern was studied in a C. cornelia population on the Muromi River, Fukuoka, Japan. Adult males intruding into another male’s territory were expelled aggressively by the resident, but they usually remained within a range of 50-60 m along the stream. On the other hand, tenerals of both sexes appearingin an adult male’s territory were not expelled, and they usually remained at the periphery of a territory. However, they were likely to move upstream during the study period. As the population density at the stream increased, mature males established their territories between the existing territories of other males.