Sebastes schlegelii is one of the most commercially important marine fish in the northwestern Pacific. However, little information about the genome-wide genetic characteristics is available for S. schlegelii individuals from the Bohai and Yellow Seas. In this study, a total of 157,778, 174,480, and 188,756 single-nucleotide polymorphisms from Dalian (DL), Yantai (YT), and Qingdao (QD) coastal waters of China were, respectively, identified. Sixty samples (twenty samples per population) were clustered together, indicating shallow structures and close relationships with each other. The observed heterozygosity, expected heterozygosity, polymorphism information content, and nucleotide diversity ranged from 0.14316 to 0.17684, from 0.14035 to 0.17145, from 0.20672 to 0.24678, and from 7.63 × 10⁻⁶ to 8.77 × 10⁻⁶, respectively, indicating the slight difference in genetic diversity among S. schlegelii populations, and their general genetic diversity was lower compared to other marine fishes. The population divergence showed relatively low levels (from 0.01356 to 0.01678) between S. schlegelii populations. Dispersing along drifting seaweeds, as well as the ocean current that flows along the western and northern coasts of the Yellow Sea and southward along the eastern coast of China might be the major reasons for the weak genetic differentiation. These results form the basis of the population genetic characteristics of S. schlegelii based on GBS (Genotyping by Sequencing). In addition to basic population genetic information, our results provid a theoretical basis for further studies aimed at protecting and utilizing S. schlegelii resources.

Objectives: Sillago japonica is a commercially important marine fish species in the Northwestern Pacific, and understanding its genetic diversity and population structure is crucial for germplasm resource conservation and elucidating population evolution mechanisms. This study specifically aimed to systematically explore the genetic diversity and population structure of S. japonica across five geographic regions (DJW, YSW, ST, ZS, and RS) in its distribution range. Methods: A total of 50 S. japonica individuals from the five geographic regions were analyzed using high-throughput mitochondrial genome sequencing data. We identified single nucleotide polymorphisms (SNPs) and insertion-deletion (InDel) loci, followed by comprehensive population genetic analyses including phylogenetic tree construction, principal component analysis (PCA), ADMIXTURE analysis, and calculation of genetic differentiation indices (Fst) and genetic diversity parameters. Results: A total of 2966 SNPs and 414 insertion-deletion loci were identified. Phylogenetic tree topology, PCA, and ADMIXTURE 1.3.0 analysis consistently showed low genetic differentiation among the five populations, a pattern supported by low pairwise Fst values ranging from 0.00047 to 0.05589, indicating extensive gene flow across regions. Genetic diversity parameters varied slightly among populations: observed heterozygosity (0.00001–0.00528), expected heterozygosity (0.04552–0.07311), percentages of polymorphic loci (19.41–30.36%), and nucleotide diversity (0.04792–0.07697). Conclusions: The low genetic differentiation and diversity observed in S. japonica populations may result from the combined effects of historical bottleneck-induced gene pool reduction and extensive gene flow. These findings provide essential theoretical support for formulating targeted conservation strategies for S. japonica germplasm resources and further studies on its population evolution mechanisms.