Germplasm Resources And Population Genetics Analysis Of Larimichthys Crocea In The Offshore Of China

Large yellow croaker(Larimichthys crocea)belongs to Vertebrata,Actinopterygii,Perciformes,Sciienidae,Larimichthys,and is one of the important commercial fishes in coastal areas in China.In this thesis,the SNP sites obtained by RAD sequencing,mitochondrial COI and Cytb gene sequences,nuclear gene RYR3 sequence and other related genetic information were used to study the status quo of the genetic structure,diversity and other genetic resources of wild and cultured large yellow croaker population in China,and explore the possible effects of proliferation release activities and their effects on wild genetic resources of large yellow croaker.This is of great significance to the formulation of large yellow croaker resource protection policies and the development of related industries.Main results are as follows:1.6,666 high-quality SNP sites of 120 large yellow croakers of 3 wild populations were obtained by RAD sequencing(wild population in Fujian and Guangdong MYW,wild population in West Guangdong and wild population in Sansha Bay in Fujian SSBW)and 2 cultured populations(cultured population in Fujian FJC and cultured population in Zhejiang ZJC).The genetic diversity showed that the observed heterozygosity(HO)for the 5 sampled populations was between 0.170 and 0.178,and that with an average inbreeding coefficient(GIS)was 0.094.The results of the Structure and Fst analysis based on SNP sites showed that there was no significant difference between MYW and YXW that were historically considered to belong to two groups(Fst=0.008).In combination with the results of AMOVA,this indicates that there is no population differentiation between the two populations.However,there was differentiation between SSBW and MYW(Fst=0.079)and YXW(Fst=0.087).Meanwhile,there also was significantly differentiation between the two cultured populations and MYW and YXW,but there was no differentiation between FJC and SSBW,indicating that there is significant release effect in SSBW.2.Mitochondrial COI gene,Cytb gene and nuclear gene RYR3 gene sequence were used to analyze 6 wild geographical population(SSBW,MYW,YXW,wild population at the border of Fujian and Zhejiang MZW,wild population in Zhoushan ZSW,wild population in Lvsi Ocean in Jiangsu JSW,591),FJC(2,414)and ZJC(371).The analysis results of genetic diversity showed that the genetic diversity in all wild populations except SSBW was at a high level(HD>0.98)and significantly higher than that in the two cultured populations.The Fst results showed that there was significant differentiation between cultured and wild populations(Fst>0.15),and that there was no differentiation between other wild populations except SSBW.The comparative analysis of the genetic structure based on shared haplotype ratio showed that SSBW and cultured populations had the maximum haplotype sharing(PSHw=47,PIHw=85%),indicating that SSBW is greatly affected by cultured populations due to proliferation release,and its genetic structure is more similar to that of cultured populations.However,the results of the analysis based on the cladogram and haplotype showed that there was no typical clustering among wild populations,and that there was a certain proportion of shared haplotypes among populations,further indicating that there is no population differentiation among various geographical populations.In the haplotype network diagram analysis,the ancient haplotypes that occupy the core mainly were wild populations,and that the haplotypes of cultured populations were mainly distributed at the end of long branches and showed multiple star-like radiation,indicating that most wild large yellow croaker individuals are not from the released ones or their offsprings.In conclusion,we hold that there are real wild populations of large yellow croaker in China.Although the resources have not been recovered,they still maintain a relatively rich level of genetic diversity.The level of the genetic exchange among different geographical populations of wild large yellow croaker in China is higher than previous estimates;and there is no differentiation among populations.Although the resources in the East China Sea region have been sharply destroyed,they can still be replenished by the migration and diffusion of populations from the north and south ends.There is significant differentiation between cultured populations and wild populations.Most individuals have relatively concentrated genotypes and low diversity.Nevertheless,the more basic breeding colonies there are(the more independent fish farms),the more effective it is to slow down this process.Only the large yellow croaker population in Sansha Bay was significantly affected by artificial releasing,which also suggests that there is a high survival rate of released individuals in this region.