Genetic effect of released brood grass carp (Ctenopharyngodon idella) on wild population in the Yangtze River inferred from microsatellite markers

The natural resources of grass carp (Ctenopharyngodon idella) in Yangtze River have significantly decreased in the past decades. In recent years, large-scale releases of brood grass carp are carried out for ecological restoration in Yangtze River. In order to assess the genetic effect of released brood fishes on wild population in the middle reaches of Yangtze River, thirteen polymorphism microsatellite markers were selected to genotype the genetic differentiation among released and wild populations. Fifteen populations were sampled, including ten released and five wild populations. The results showed that polymorphic information content and gene diversity of the microsatellite loci was 0.8622 (0.657–0.950) and 0.8555 (0.675–0.936), respectively. The number of effective alleles of the 15 populations ranged from 7.4503 to 10.1536, and allelic richness from 11.483 to 15.204, which indicated that genetic diversity of grass carp populations was moderately high. The total and pairwise genetic differentiation indexes (F_ST) were low to 5%, loci implying that there was no significant genetic differentiation among populations. The 15 grass carp populations were divided into 4 groups based on Bayesian clustering analysis and principal component analysis. According to above grouping and geographic distribution of the 15 grass carp populations, we have conducted AMOVA analysis, as a result, most of the genetic variation of grass carp populations came from inter-individuals, and the level of genetic differentiation among groups was low (F_CT<5%;F_SC<5%). In summary, there was hardly any genetic effect of releasing nature grass carp on wild populations in the Yangtze River under current model.