DISTRIBUTION AND LIFE-HISTORY OF TRACHIDERMUS-FASCIATUS IN RIVERS AROUND ARIAKE SOUND, KYUSHU, JAPAN

The distribution and life history of the catadromous cottid fish, Trac hidermus fasciatus were studied in rivers discharging into Ariake and Yatsushiro Sounds, west Kyushu, Japan. The fish were found to inhabit rivers located between the Yabe River of Fukuoka Prefecture and the Ho nmyo River of Nagasaki Prefecture. Juveniles were found in May pointin g upstream just below dams which were located at the lowest point in t he rivers. Until their first autumn, the fish remained in small areas below the dams. Most of the dams were located at the upper end of the tidal reaches of the rivers. We did not find T. fasciatus inhabiting a reas above the lowest dam. Their present distribution, which is restri cted down-stream and confined to unnaturally small areas, is thought t o be caused by the construction of the dams. The fish do not appear to migrate as far upstream as previously reported. The fish mature and m igrate downstream in their first autumn or winter, when they are about 150 mm in total length. No age 2 fish were found in the rivers survey ed. Juveniles smaller than 19 mm in total length mainly fed on copepod s, and their main food changed from aquatic insects to fish after thei r upstream migration.