Development of a repetitive DNA marker for identification of the exotic large-scale loach introduced to Japan

The large-scale loach Paramisgurnus dabryanus is a freshwater fish native to East Asia except for Japan. However, its presence has been observed in various locations of Japan, and sympatric occurrences with the dojo loach Misgurnus anguillicaudatus, a related species native to Japan, have also been reported. Artificially induced inter-specific hybrids between the two species were reported viable, and their fertility was suggested at least in females. To avoid genetic introgression in native Japanese dojo loaches, a method for precise identification of the two loach species is necessary. Species identification based on morphology has sometimes led to misidentification in the Japanese population, and inter-specific hybrids were difficult to identify due to their morphological similarities. We therefore developed a nuclear DNA marker named PdaDra from repetitive sequences isolated by genomic DNA digestion with the restriction enzyme DraI. This marker could discriminate large-scale loaches from dojo loaches, showing predominant smear-like electrophoretic patterns with ladder-like bands in the large-scale loach and no amplification in most dojo loaches. The combined use of other DNA markers previously developed for the dojo loach also makes it possible to successfully identify inter-specific hybrids. The PdaDra marker thus provides quick and accurate identification of the large-scale loach and its inter-specific hybrids.