The populations in most of Japan (Honshu and Kyushu) are likely introduced from China. The population in the Nara Basin was introduced from Korea in the beginning of the 20th century. Its distribution in Japan is discontinuous, which also indicates that it is introduced within the last millennium or so. The eels found in Taiwan appear to belong to two different species, a Japanese form was introduced in 1940, but a Southeast Asian form is also common and may have also been introduced or be native. The eels were first introduced to the Oahu in Hawaiian Islands around 1900, where they still occur.