Abstract
The brown trout (Salmo trutta L.) iswidely distributed all around Europe but its naturaldiversity is threatened by massive stocking withAtlantic domestic strains. Describing the remainingnatural genetic diversity and the proportion of domestichatchery strains in rivers is a prerequisite for smartconservation. The high genetic diversity of browntrout populations around the Tyrrhenian Sea is wellknown. Use of twelve microsatellites has alloweddescription of the natural genetic structure ofpopulations and detection of the consequences ofstocking. Mitochondrial DNA control regionsequences and the LDH-C1* gene enabled placementof each population into one of the six mitochondrialand two allozymic known evolutionary lineages. TheCorsican populations showed low intra-populationgenetic diversity but an exceptionally high level ofinter-population differentiation. More southernTyrrhenian regions exhibited opposite pattern ofdiversity, partly due to the Atlantic domestic introgression.Globally, the natural structure outlines twonorth–south clines: high inter-population differentiationand predominance of the Adriatic lineage in thenorth, but lower inter-population differentiation andthe presence of the natural Atlantic lineage in thesouth. In addition, the Tyrrhenian region is the contact zone between the widespread Adriatic lineage and alocal natural Atlantic lineage probably coming fromNorth Africa through the Strait of Gibraltar.