Foreign eel species in the natural waters of Japan detected by polymerase chain reaction of mitochondrial cytochrome b region

Species identification of 1,048 eel individuals, collected in the natural w aters of middle and western Japan from August 1997 to February 1998, has be en performed by polymerase chain reaction (PCR) of the mitochondrial DNA (m tDNA) cytochrome b region. The majority of the individuals (832, 79.4%) wer e identified as Japanese eel Anguilla japonica, The other individuals (216, 20.6%) were thought to be European eel A. anguilla based on the analysis o f PCR restriction fragment length polymorphism (PCR-RFLP), The European eel s were found in the samples from Shinjiko Lake (161 out of 513, 31.4%) and Mikawa Bay (55 out of 443, 12.4%). European eel is not a native species in Japan. The possible reasons for the existence of this species in the natura l waters of Japan and its influence on the natural resource of Japanese eel are discussed.