Studies On Ploidy Identification Of Carassius Auratus Beimin Var.

Polyploidization is a common phenomenon in fish,and it is one of the significant promoters of biological evolution and speciation.Except for its important economic value,Carassius auratus is an ideal species to study polyploidization in fish evolution processes.C.auratus beimin var.originates from Beimin Lake,Hunan.Compared to other Carassius,C.auratus beimin var.had a higher growth ratio and larger body size,and we therefore hypothesise that these growth advantages were related to polyploidization.In order to explore the biological characteristics and ploidy level of C.auratus beimin var.,483 samples were randomly collected in Beimin Lake,from2016 to 2017.The results showed that there were no significant differences in the countable characters of C.auratus beimin var.in different age groups,and there were significant differences in the number of spines of the dorsal fin compared with C.pengze var.,C.auratus qihe var.and C.auratus gibelio.There was no significant difference in the body shape of C.auratus beimin var.at all ages,and all showed a similar growth trend.The difference in traits was mainly concentrated in the head of the fish.Compared with other C.auratus,the differences were mainly concentrated in the tail stalk.By calculating the coefficient of variation of each age group,it was concluded that the trait was stable and there was no variation in growth.To test this hypothesis,a 9 microsatellite ploidy identification method was developed to examine the ploidy level of C.auratus beimin var.,and flow cytometry assays and chromosome karyotype assays was used to further confirm the findings.The results showed that 9 microsatellites could completely distinguish 37 ploidy-known specimens.The genotyping results showed that all the 136 ploidy-unknown individuals are triploid,all three genotypes(AAA,AAB/ABB,and ABC)were observed in this population.The mean DNA contents of blood cells in C.auratus beimin var.(159.42±5.64)was 1.5 times with that of blood cells in C.auratus red var.(102.43±3.54),and the results from microsatellite markers are totally concordant with those from flow cytometry analysis.The karyotype analysis revealed that the number of chromosomes is 156± and the karyotypic formula was 3n=39m+36sm+81sta,NF=231.This study not only established a microsatellite marker system for ploidy identification of C.auratus,but also systematically confirmed that C.auratus beimin var.is triploid.