抄録
At the beginning of this century, the swamp-eel Monopterus albus was introduced from Korea to an area of Nara Prefecture, located at or near one of the origins of the Kizu, Yamato and Yoshino River Systems. Our samplings were carried out between 1988 and 1997 and information offered by farmers was confirmed that the fish was distributed in the three river systems. Furthermore, a comparison between our results and previous reports clearly shows that the fish has expanded its distribution range. Closer surveys revealed that the fish did not occur at higher altitudes which were isolated from lowland fields providing a habitat for the fish, even though both area were cconnected by rivers. In contrast, it occured in paddy fields on both sides of passes which the fields traversed. The fish seems to be a poor swimmer because of its degenerate fins. These facts suggest that its wide distribution range is due to its high dispersal ability and some extrinsic factors as suggested below: 1) ability to breathe air, which enables it to leave bodies of water; 2) release at or near the origins of the three river systems; 3) abundance of contiguous paddy fields which are suitable habitats for the fish.
