Assessing Genetic Diversity and Population Structure of the Endangered Freshwater Fish Gobiobotia brevibarba for Conservation Genetics in Korea

The endangered freshwater fish Gobiobotia brevibarba is endemic to Korea and threatened by habitat disturbance in major river systems. We investigated four wild populations from the Han River basin (IJR, BHR, NHR) and the Geum River basin (GR) using eleven microsatellite loci to assess genetic diversity, population structure, and contemporary gene flow. All populations showed relatively high genetic diversity (HO = 0.709–0.800, HE = 0.707–0.803) and no evidence of inbreeding, although bottleneck signals under the infinite allele mutation model were detected in IJR and BHR. Contemporary effective population size was large in IJR (Ne = 2463) and moderate in NHR (Ne = 467), whereas estimates for BHR and GR were imprecise. Genetic differentiation was very low within the Han River basin (FST = 0.009–0.027) but weak and significant between Han and Geum (FST = 0.085–0.096), and clustering analyses (STRUCTURE, DAPC, find.cluster) consistently supported K = 2, separating Han from Geum River. Gene flow analyses indicated extremely limited interbasin gene flow (<4%) but asymmetric contemporary migration from BHR into both IJR and NHR; all other migration rates were similarly low. These results show that G. brevibarba currently maintains high genetic diversity and two basin-level genetic clusters, underscoring the need to manage Han and Geum River populations as separate units and conserve riffle habitats and longitudinal connectivity.