Abstract
The 137 individuals of Johnius grypotus were collected from seven localities from the Bohai Sea to the East China Sea. A 549 base pair (bp) fragment of the hypervariable region of the mtDNA control region was sequenced to examine genetic diversity and population structure. The populations of J. grypotus showed high haplotype diversity (h) with a range from 0.7500 to 0.9740 and low nucleotide diversity (π) with a range from 0.0024 to 0.0067. Low and non-significant genetic differentiation was estimated among populations except for North Yellow Sea population, which has a significant genetic difference with other populations. The demographic history examined by mismatch distribution analyses and Bayesian skyline plot (BSP) analyses revealed that a sudden population expansion occurred almost 20 to 40 thousand years before. Relatively recent population expansion in the last glacial period, large dispersal of eggs or larvae carried by coastal current, and the homogeneity of living environment may have an important influence on the population genetic pattern.