Contrasting Genetic Structures Among Populations of Two Hexagrammid Fish Species in the Northwestern Pacific

The genetic diversity and population structure of the fat greenling (Hexagrammos otakii) from the seven coastal locations in China, Korea, and Japan and the Okhotsk atka mackerel (Pleurogrammus azonus) from two coastal locations in Korea and Japan were investigated using the mitochondrial DNA (mtDNA) control region sequences. Sequences from 231 individuals (sequence length: 436 bp) inferred 105 haplotypes in the H. otakii, and sequences from 50 individuals (sequence length: 404 bp) inferred a single haplotype in the P. azonus. The haplotype and nucleotide diversities ranged from 0.737 to 0.981 and 0.007 to 0.010, respectively, for the H. otakii, whereas both diversity indices were zero for the P. azonus. Pairwise FST statistics for the H. otakii showed genetically structured populations for Liaoning (China), Eoeundol (Korea), and Hyogo (Japan). Mismatch distribution analysis showed that all of the H. otakii populations experienced an expansion in the Late Pleistocene period, approximately 0.096–0.193 MY before the present. Meanwhile, it was found that P. azonus needs more sensitive markers than mtDNA control region and more samples to reveal genetic diversity and population structure. As a result, the present study revealed that even fish belonging to the same family and with the same ecological characteristics may have different genetic diversity.