Analysis Of Genetic Diversity And Structure Of Silver Carp In Yangtze River, Ganjiang River And Poyang Lake

Silver carp(Hypophthalmichthys molitrix) is one of the four major Chinese carps, has been one of the most important traditional freshwater aquaculture species in China. The Yangtze River and its attached lakes are main home to silver carp. However, due to long-term overfishing, environmental pollution, inconnectivity between the mainstream and the attached lakes, water conservancy and hydropower engineering, the Yangtze River wild silver carp stock resources continued to decline which could affect genetic resources. Therefore, it is necessary to assess the silver carp germplasm resources in Yangtze River. In this article, in order to provide basic information for protecting silver carp germplasm resources in Yangtze River, microsatellite markers and mitochondrial D-loop sequence were used to analyze genetic diversity, genetic structure and genetic differentiation of silver carp stocks in Yangtze River, Ganjiang River and Poyang Lake.Nine microsatellite markers were employed to analyze the genetic structure of eight silver carp stocks from Pengze and Xintanhou in Yangtze River, Hukou, Yugan, Poyang and Yongxiu in Poyang Lake, Ganzhou and Xingan in Ganjiang River. A total of 125 alleles were detected in total 314 individuals. The number of alleles per locus ranged from 6 to 26, the average observed heterozygosity ranged from 0.766 to 0.846, the average expected heterozygosity ranged from 0.813 to 0.833, which indicated that genetic diversity in eight silver carp stocks was high. The genetic similarity coefficient ranged from 0.8986 to 0.9771, the genetic distance ranged from 0.0231 to 0.1069, the fixation index Fst values ranged from-0.0070 to 0.0272, AMOVA analysis showed that genetic variation mainly came from within populations with genetic variation among populations accounting only for 0.49% and that within groups accounting for 99.51%.It revealed that genetic consistency was high, the genetic distance was small and the genetic differentiation was not significant. Paternity test and gene flow analysis by microsatellite showed that, there were frequent gene exchanges between Poyang Lake, the Yangtze River and Ganjiang River silver carp stocks. Both Yangtze River and Ganjiang River silver carp stocks could be the recruitment for Poyang lake, and silver carp in Yangtze River and Ganjiang River could exchange genes through Poyang Lake freely.The mitochondrial D-loop sequences of a total of 180 silver carp specimen sampled from Yangtze River, Ganjiang River and Poyang Lake were sequenced. 47 haplotypes were detected. Average haplotype diversity(h) was 0.9137 and nucleotide diversity(Pi) was 0.016092, the high value of h and Pi means high genetic diversity of silver carp stocks in Yangtze River, Ganjiang River and Poyang Lake, which indicated the silver carp stocks were stable, and had a long evolutionary history. Genetic variation between Yangtze River, Ganjiang River and Poyang Lake(genetic differentiation among groups) was 0.02325 and genetic differentiation within populations was 0.01775, both these two values were not significant. The gene flow(Nm) between Yangtze River, Ganjiang River and Poyang Lake was 18.23. AMOVA analysis indicated that genetic variation among groups only accounted for 2.33%, genetic variation within populations accounted for 98.22%, which indicated that genetic variation among Yangtze River, Ganjiang River and Poyang Lake mainly came from the interior populations.In view of both micromicrosatellite markers and mitochondrial D-loop sequence analysis results, we found that genetic diversity of eight silver carp stocks in Yangtze River, Ganjiang River and Poyang Lake was high. Silver carp in Poyang lake came from both Yangtze River and Ganjiang River, silver carp in Yangtze River and Ganjiang River could exchange genetic information through Poyang Lake, there was no remarkable genetic differentiation between Yangtze River and Ganjiang River.