Brown trout in Japan − introduction history, distribution and genetic structure

Brown trout Salmo trutta L. lives mainly in European rivers and is also bred in hatcheries for fishery purposes. Since the end of 19th century it has been introduced in all other continents. For the present survey most of the known self-sustaining brown trout river populations in Japan have been sampled and analyzed through sequences of the entire mitochondrial DNA control region and twelve microsatellites. In Japan, brown trout are genetically not homogeneous, probably as a consequence of several introductions, one in the Azusa river and at least one other in the remaining territory. The Chuzenji hatchery houses a genetically very distinct strain, probably due to intense manipulation in isolated scientific experimentations over 30 years. Finally, most populations showed high genetic diversity (Mamachi, Kane and Odori streams, Lake Chuzenji) with the exception of the Azusa river samples. This molecular analysis clearly demonstrates a European north Atlantic origin arrived in two distinct ways.