Construction And Application Of Microsatellite Gene Bank Of Released Brood Grass Carp

Grass carp Ctenopharyngodon idellus, an important cultured freshwater fish in China, is one of the four major Chinese carps. Resent years, due to the water environmental pollution, dam construction and overfishing and so on, the natural habitation of grass carp in Yangtze River has been disturbed and destructed, which leads to the serious decline of grass carp resources. In order to recover the resources, grass carp enhancement every year has been performed in Yangtze River. However, research about effects of grass carp releasing on nature resource is limited at present. In this study, 13 microsatellite loci were used to construct a microsatellite gene bank of brood grass carp released in middle Yangtze River in 2011 to 2015. We also evaluated the genetic effect of released brood grass carp on wild population. The parentage analysis was used to assess the enhancement effect. The main results were as follows:1. A microsatellite gene bank was constructed using thirteen microsatellite loci were for brood grass carp released in Hubei section of the Yangtze River in 2011 to 2015 containing 10 released groups of 2516 fishes which come from Jianli county and Shishou county. These released population showed high genetic diversity, the average number of alleles was 34.46, the average polymorphic information content(PIC) 0.8585, the average observed heterozygosity 0.8445, and the average expected heterozygosity 0.8695.2. Microsatellite DNA molecular markers and parentage assignment technology were used to evaluate relationships between released fishes and larvaes cellected from Yangtze River. The combined exclusion probability of the 13 microsatellite loci was 99.85%, and 160 larvaes were identitified to be offsprings of released brood grass carp. The rates of the offspring of released brood grass carp among early life in middle Yangtze River from 2011 to 2015 were 6.395%, 6.422%, 9.708, 13.602% and 14.316%.3. The Thirteen polymorphism microsatellite markers were also used to analyse 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 was 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(FST) 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, the result of AMOVA analysis showed that most of the genetic variation of grass crap populations was from inter-individuals, the level of genetic differentiation among groups was low(FCT < 5%; FSC < 5%). In summary, there was hardly genetic effect of releasing mature grass carp on wild populations in the Yangtze River under current model.