筑後川におけるニゴイの回遊について

Abstract

Distribution and migration of the cyprinid fish Hemibarbus barbus in the Chikugo River were studied during 1986 and 1989. Many mature males and females were caught at the middle reaches in April, whereas most of the subadult fish were caught in the tidal reaches all the year round. According to monthly changes of gonadosomatic index of adult fish, it is clear that this fish spawns mainly in April. In order to elucidate the spawning run, 195 mature fish were marked at the tidal reaches during February and March, 1988, and 4 specimens were recaptured at the middle reaches in early April, 1988. In the tidal reaches, most of the fish were caught in waters less than 0.2 percent in salinity. Yearling fish were recognized in the lower reaches in May and began to be collected in the tidal reaches in July. These observations indicate that the yearling migrates from the lower reaches to the fresh water area of the tidal reaches. After staying there for 3-4 years, mature males and females run up for 20-40km for spawning in spring. Migration occurring wholly within fresh waters is called potamodromous migration. It seems that the migration of H. barbus in the Chikugo River is potamodromous migration and classified as an anadromous migration type.