Genetic Diversity Of Silver Carp And Grass Carp In The Middle And Upper Reaches Of Yangtze River

The Yangtze River is the main natural germplasm reservoir for the four major species of fish,which are not only the most important freshwater fish in China,but also the important species in the freshwater ecosystem.In the past few decades,on the one hand the scale of fish farming has been expanding,while the natural resources of the Yangtze River fish are in constant decline on the other hand.Since the 1990s,China has built seven germplasm repositories（original seed farms）in the middle and lower reaches of the Yangtze River as one of the measures to protect the original germplasm resources of the four major species.Assessing the genetic diversity status of the natural population,breeding population and germplasm repository of tetrahymena is important for the exploitation and conservation of tetrahymena germplasm resources,and also provides a reference basis for further scientific management of tetrahymena germplasm resources.In this study,microsatellite molecular markers were used to analyse the genetic diversity and genetic structure of silver carp and grass carp populations from the natural waters of the Yangtze River,captive breeding and germplasm banks,and to compare the magnitude of genetic diversity and the degree of genetic differentiation between and within populations.The main findings are as follows:1.Genetic diversity and genetic structure of silver carpA total of 434 samples from six natural populations（Jiangjin,Fengdu,Gongan,Yueyang,Hukou and Duchang）,four breeding populations（Meishan,Yongchuan,Changshou and Wuhan）and three germplasm bank populations（Laohe Original Breeding Farm,Laojiang Original Breeding Farm and Changsha Original Breeding Farm）in the middle and upper reaches of the Yangtze River were analysed using 13microsatellite loci.A total of 133 alleles were detected,the number of alleles in each population ranged from 8.942-11.026,the effective allele number ranged from 5.483-6.525,the Shannon diversity index ranged from 1.791-1.961,the observed heterozygosity ranged from 0.681-0.814,the expected heterozygosity ranged from0.771-0.805 and the unbiased expected heterozygosity ranged from 0.788-0.817.Comparison of interpopulation The F_ST range between the 13 populations was 0.008-0.073,indicating that the overall genetic differentiation between the 13 chub populations was small（p<0.05）,with a greater differentiation between the long-lived population and the other 12 populations.populations ranged from 2.972-32.954,with the lowest degree of gene exchange between the Changshou and Wuhan populations and the most frequent gene exchange between the Laojiang River Original Breeding Farm and Laohe Original Breeding Farm populations.The results of the AMOVA analysis of the different groups did not reveal any particularly significant genetic differentiation between and within groups of the three chub populations,with the main genetic variation contributed by inter-individual differences.both the Structure and PCo A results showed that the breeding populations differed slightly from the natural and germplasm bank populations,and overall the genetic composition of the three chub populations did not differ significantly from each other.2.Genetic diversity and genetic structure of grass carpA total of 411 samples from six natural populations（Yibin,Jiangjin,Fengdu,Jianli,Hukou and Yongxiu）,three breeding populations（Linxiang,Yuanjiang and Jingzhou）and three germplasm repository populations（Laohe Original Breeding Farm,Laojiang Original Breeding Farm and Changsha Original Breeding Farm）of grass carp from the middle and upper reaches of the Yangtze River were analysed using 13 microsatellite loci.A total of 130 alleles were detected,the number of alleles in each population ranged from7.179-12.821,the effective number of alleles ranged from 3.870-6.531,the Shannon diversity index ranged from 1.361-2.004,the observed heterozygosity ranged from0.509-0.756,the expected heterozygosity ranged from 0.606-0.797,the unbiased expected heterozygosity ranged from 0.616-0.807,and the inbreeding coefficient of The F_ST range between the 12 populations was 0.008-0.194,indicating that the overall genetic differentiation among the 12 grass carp populations was small（p<0.05）,with two populations,Jingzhou and Yuanjiang,having the lowest genetic diversity and the highest inbreeding coefficient,and the natural population and the germplasm bank population having little difference.Gene flow between the 12 populations ranged from 1.042-32.309,with the lowest level of gene exchange between the Jingzhou and Laojiang River populations and the most frequent gene exchange between the Laojiang River Original Breeding Farm and Laohe Original Breeding Farm populations.The results of AMOVA analysis of the different subgroups showed that the genetic variation values of the three grass carp populations were mainly from inter-individual differences,and there was also some degree of genetic differentiation between groups(F_ST=0.159),and the genetic differentiation between groups was mainly contributed by the breeding populations.both Structure and PCo A results showed significant genetic differentiation between the three groups.Overall,the genetic levels of silver carp and grass carp in the Yangtze River Basin are still at a high level.No significant differentiation occurred among the three silver carp populations in the middle and upper reaches of the Yangtze River,while some genetic differentiation occurred in the cultured populations of the three grass carp populations.It is recommended that a census of genetic resources be carried out for the grass carp cultured populations,while supervision should be strengthened to avoid degradation of germplasm resources.