Abstract: Twelve microsatellites were used to analyze the genetic diversity and genetic structure of eight wild populations of grass carp, among which six populations from Yangtze River (Hanjiang, Wujian, Jiujiang, Shishou, Mudong, and Wanzhou), one population from Pearl River and Heilongjiang River for each, Zhaoqing, and Nenjiang, respectively. Twelve markers showed highly polymorphic and all the eight populations contained high genetic variations. The variations of six populations of Yangtze River and Zhaoqing population of Pearl River were higher than Nenjiang population of Heilongjiang River. Bottleneck analysis revealed that four populations (Zhaoqing, Nenjiang, Mudong, and Wangzhou) had experienced a recent genetic bottleneck, and the effective population size was reduced. Pairwise F_ST and AMOVA analysis detected significant genetic difference among populations. The pairwise population genetic distances and the UPGMA tree demonstrated that the genetic distances between six populations of Yangtze River and Zhaoqing population were closer and clustered together earlier, as compared to those populations with Nenjiang population. The genetic structure simulation analysis suggested that there were five logic populations of all individuals. The genetic structures of Zhaoqing and Nenjiang populations were shown with independent separation, but the genetic structures of populations from Yangtze River were shown with fuzzy distribution. The high diversity was found in the wild grass carp from three major watersheds in China, which would supply a basis for future genetic improvement. However, the bottleneck effect of some populations should be taken into account in the practical breeding programs.

Key words: Ctenopharyngodon idella, wild population, genetic diversity, bottleneck effect, genetic structure