FEEDING HABIT OF A CYPRINID FISH HEMIBARB US-BARBUS IN THE CHIKUGO RIVER, KYUSHU, JAPAN

The yearlings of a cyprinid fish Hemibarbus barbus of the Chikugo Rive r, Kyushu, Japan, migrate down to the lower reaches and further to the freshwater area of tidal reaches within a year after hatching. After staying there for 3-4 years, mature fish run up to the middle reaches for spawning in spring. In order to elucidate the feeding habit of H. barbus, we examined the gut contents of 822 specimens collected during 1986 and 1987. The yearling 10-20 mm in standard length (SL) fed on z oo-plankton (rotifers, cladocerans, copepods), and that of 20-40 mm SL fed on mainly copepods in the lower reaches. Depending on their growt h, they gradually changed feeding items from zoo-plankton to benthic a nimals such as chironomid larvae. Then, the yearling over 50 mm SL hav ing pharyngeal bones which formed the same shape as those of adult fis h began to crush and feed on corbiculids and ephemerid larvae. After m igrating down to the tidal reaches, they also fed on benthic animals ( chironomid larvae, corbiculids, polychaetes). Elvers of the Japanese e d Anguilla japonica and the young mitten crab Eriocheir japonicus occu rred in the guts of 2-year-old and older fish.