Occurrence of length polymorphism and heteroplasmy in brown trout

Length polymorphism was observed in the mitochondrial DNA (mtDNA) control region (CR) of brown trout (Salmo trutta). Length variability was due to the presence of an 81 or 82 bp tandem duplication segment located in the 3′ hypervariable domain of the mtDNA CR in specimens from two European river basins, in the north-western Iberian Peninsula and in north-eastern Germany. Tandem repeated motifs were present in one to three extra copies. In the Miño river basin of the Iberian Peninsula some specimens revealed heteroplasmy. Such unique genetic structures of brown trout may provide useful information about the adaptive evolution of single populations and further explain the influences causing heteroplasmy.