Abstract: To investigate genetic diversity of Rhodeus ocellatus from Lancang River of Yunnan,this study applied PCR amplification and sequencing methods to determine the mitochondrial COI gene sequence fragments of 10 R. ocellatus samples from Xishuangbanna.Additionally,we combined with the homologous sequence of COI gene of six Rhodeus species from GenBank database to execute the genetic diversity,genetic distance and phylogenetic analyses.Sequence analyses showed that the COI gene sequence fragments was 657 bp,the base composition A+T content (52.5%) was larger than the G+C content (47.5%),and there were 21 variable sites and 4 haplotypes.The haplotype diversity of R. ocellatus was 0.711,the nucleotide diversity was 0.008 2,the average nucleotide difference was 5.400,and the Tajima's D value was -1.353 78 (P>0.10).The minimum genetic distance between our R. ocellatus samples and R. ocellatus from Baoshan city was 0.005,and the maximum genetic distance between R. ocellatus samples and R. notatus was 0.196.Phylogenetic analysis showed that R. ocellatus samples were clustered into a monophyletic branch with the same sequence published from Baoshan city with high bootstrap value (100%).Furthermore,the R. amarus,R. colchicus and R. meridionalis samples clustered together as a monophyletic clade,while R. notatus and R. uyekii samples were gathered to form a monophyletic branch.

Key words: Rhodeus ocellatus, COI gene, genetic diversity, phylogenetic relationship