ECOLOGY OF AN ATYID SHRIMP CARIDINA JAPONICA (DE MAN, 1892) MIGRATING TO UPSTREAM HABITATS IN THE SHIWAGI RIVULET, TOKUSHIMA PREFECTURE

Abstract

The ecology of an atyid shrimp Caridina japonica was studied in the Shiwagi Rivulet. Yuki Town, Tokushima Pref. This species is amphidromous in nature. The juveniles migrate upstream from the sea exclusively during the night and can be seen climbing a vertical wall, where the rivulet water is trickling down. From field observation, rheotaxis seems, to be the most important orientation mechanism for the upstream migration of juveniles. The peak month of egg incubation was June. The mean duration of incubation was 40 days at 20℃ in aquaria. From these values and with known information on the duration of larval life, it was estimated that the period of upstream migration starts in August. Most males die within two years after metamorphosis, however, many females survive for more than two years.