The North American channel catfish Ictalurus punctatus, an invasive freshwater fish introduced to Japan for aquaculture in the 1970s, has become established in several rivers and lakes, with subsequent detrimental effects on local fisheries and other freshwater fauna. The origin and invasive distribution of channel catfish in Japan was assessed from the geographical distribution of mtDNA haplotypes of channel catfish populations, utilizing partial (412 bp) nucleotide sequences of the mtDNA control region from 174 individuals collected from 7 localities. A total of 12 haplotypes (J01–J12) were found in Japanese freshwater systems. Populations in eastern Japan (Fukushima and Ibaraki Prefectures) and a fishing pond in Aichi Prefecture were characterized by many haplotypes, shared among those localities. However, the haplotype compositions of populations in western Japan (Yahagi River, Aichi Prefecture and Lake Biwa water system, Shiga Prefecture) differed from the former and also from each other. A phylogenetic analysis using Japanese (nonindigenous), Chinese (non-indigenous) and United States (indigenous) haplotypes indicated that all of the Asian haplotypes were included in "Lineage VI," distributed over a wide area of the United States, confirming that lineage as the primary source of introduced Asian populations. However, the introduction of channel catfish into Japan occurred on at least three occasions (in eastern Japan, Yahagi River and Lake Biwa water system).
