Population genetics and the importance of migration in the facultative migratory fish, Labeo chrysophekadion, in the Lower Mekong Basin

The Mekong River Basin, a critical biodiversity hotspot, is facing growing threats from environmental degradation and human activities, particularly dam construction. This study investigates the population structure and migratory behavior of Labeo chrysophekadion, an important food fish and widespread migratory species found in varied habitats, using restriction-site associated DNA sequencing. Treemix, Structure, and PCA analyses using an EzRAD derived neutral SNP dataset supported the subdivision of populations into three distinct zones corresponding to the Upper, Middle, and Lower Mekong regions. The analyses also provided evidence of both upstream and downstream migration pathways, including upstream through the Khone Falls. Active upstream adult migration apparently supports a peak in observed heterozygosity within the middle Mekong. Downstream dispersal best explains a large proportion of genetic material originating from the Upper into the Middle and Lower Mekong regions, and Middle into the Lower Mekong region. These findings emphasize the importance of managing this species as migratory, with special attention to the impacts of dam construction, to maintain healthy levels of genetic diversity.