An Exploratory Analysis of Genetic Structure and Introgression in Salmo trutta Populations from Campania Rivers.

The Salmo trutta complex exhibits high genetic and phenotypic diversity due also to the historical climatic events and colonization processes. In Europe, several evolutionary lineages have been identified, including the Atlantic and Mediterranean. In Italy, native Mediterranean trout populations have been threatened by restocking practices involving hatchery-reared fish of Atlantic origin, thus resulting in widespread hybridization and genetic introgression. This study aimed to genetically characterize trout populations from selected river basins of the Campania region (southern Italy) and to assess whether the observed morphological characteristics, consistent with standard morphological descriptions of Mediterranean trout, were supported by genetic evidence (i.e., LDH-C1* locus and microsatellite markers analyses). The results revealed a complex genetic structure of Salmo trutta populations in Campania, with evidence of Atlantic introgression in several river systems. Differences between LDH-C1* genotyping and microsatellite data highlighted the importance of using multiple genetic markers to accurately detect hybridization and identify lineage composition. These explorative results have also evidenced that specific populations (i.e., those from Imperatore, Sava, and Volturno rivers), showed genetic features consistent with Mediterranean ancestry. The findings highlight the importance of genetic analyses not only for accurate species identification beyond morphology but also for supporting conservation strategies to protect native Mediterranean trout and guide restocking based on local genetic resources.