Origin and introduction history of self-sustaining rainbow trout populations in Europe as inferred from mitochondrial DNA and a Y-linked marker

Following its introduction in the late nineteenth century, rainbow trout gradually spread to become one of the most widespread non-native fishes. Nevertheless, despite continuous introductions, they have become self-sustaining in only a limited number of European rivers, most of which are located in the Prealps. There is no consensus on the reasons for the absence of self-sustaining populations over most of Europe, though genetic differences have been suggested as a potential underlying factor. We conducted a population genetic study of the structure and origin of European populations to help resolve these questions. We examined variation in mitochondrial D-loop and the Y-linked marker of 41 self-sustaining, stocked, and hatchery populations from Europe and compared them to native and hatchery populations in North America. High levels of genetic diversity but little inter-population genetic variation suggests that European populations are derived from multiple sources, with a great majority of parental populations belonging to steelhead and coastal rainbow trout from Central and Northern California. Our study revealed no considerable genetic differences among European self-sustaining, stocked, and hatchery populations. The mitochondrial DNA data do not allow evaluation of selection and adaptive traits and thus cannot explain potential population differences arising in their naturalization success.