Genetic diversity of endangeredChondrostoma nasusin the River Rhine system: Conservation genetics considerations on stocking and reintroduction

Reintroduction, stocking and translocation of freshwater fish are of growing concern given their importance for biodiversity conservation and ecosystem functioning. For successful management and stocking programmes, it is essential to incorporate genetics-based approaches. The nase (Chondrostoma nasus) constituted one of the most common fish species in European rivers. Its highly specialised and migratory nature exposed the species to human pressures, and thus, promoted its decline. Current knowledge of the genetic structure ofC. nasusis considerably limited for Europe as a whole and for Germany specifically. To overcome this lack of information we present original data onC. nasusfrom different tributaries of the River Rhine. We analysed nine microsatellite markers and mtDNA Cytochromebsequences to assess the distribution of genetic diversity and structure of this species across the study area. With the exception of the Lake Constance/Alpine Rhine population,C. nasusexhibited high gene flow within the Rhine system, and therefore, limited geographical genetic differences between populations where migration is not prevented by human intervention. The present study provides new insights into the levels of genetic variability ofC. nasusin the Rhine system, providing useful information for guiding reintroduction and stocking programmes. Population genetic information will improve future preservation and management of this valuable freshwater fish species in Germany and beyond.