The common snook is one of the most abundant and economically important species in the Usumacinta basin in the Gulf of Mexico, which has led to overfishing, threatening their populations. The main goal of the present study was to assess the genetic diversity and structure of the common snook along the Usumacinta River in order to understand the population dynamics and conservation status of the species. We characterized two mitochondrial markers (mtCox1 and mtCytb) and 11 microsatellites in the Usumacinta basin, which was divided into three zones: rainforest, floodplain and river delta. The mitochondrial data showed very low diversity, showing some haplotypic diversity differences between the rainforest and delta zones. In contrast, we consistently recovered two genetic clusters in the Usumacinta River basin with the nuclear data in both the DAPC and STRUCTURE analyses. These results were consistent with the AMOVA analyses, which showed significant differences among the genetic clusters previously recovered by DAPC and STRUCTURE. In terms of diversity distribution, the floodplain zone corresponded to the most diverse zone according to the mitochondrial and nuclear data, suggesting that this is a transition zone in the basin. Our results support the relevance of the molecular characterization and monitoring of the fishery resources at the Usumacinta River to better understand their connectivity, which could help in their conservation and management.