LAUSR

Abstract The Northwest Pacific marginal waters comprising the South China Sea, East China Sea, Yellow Sea, and the Sea of Japan have unique geomorphic features. The Japanese flounder Paralichthys olivaceus, which is endemic to the Northwest Pacific, has high nutritional, economic, and ecological value. To allow the examination of the demographic history and population structure of the most common P. olivaceus species range over the five marginal seas (East China Sea, Yellow Sea, Bohai Sea, Northwest Pacific Ocean, and the Sea of Japan), the mitochondrial DNA control region of 91 individuals from six populations in China was sequenced. These sequences were combined with 233 sequences from four populations distributed in the Northwestern Pacific Ocean for analysis. Higher levels of nucleotide diversity (0.032 ± 0.016) and haplotype diversity (0.996 ± 0.001) were observed. The peripheral Fuqing population in the East China Sea had the relatively lowest genetic diversity and highest differentiation. Furthermore, when the results of the isolation by distance test, spatial analysis of molecular variation and geographic barrier analysis are also considered, there is a clear need to prioritize resource conservation and enhancement measures in this area. The phylogenetic trees, structure assignment test, and haplotypes network revealed no significant differences in the genealogical structure among ten populations. Mismatch distribution analysis, Bayesian skyline plots, and neutrality tests suggested that P. olivaceus experienced population expansion during the Pleistocene. Ocean currents and climate change play important roles in shaping the geographical distribution and genetic population structure of P. olivaceus.