Characterization of sex locus and sex-specific sequences in the mandarin fishes

Sex determination of teleost fish switched frequently. Sex markers are especially practical in identifying early sex and helpful in generating mono-sex population in aquatic species. And sex determination in mandarin fishes is still unclear. In this study, we applied a pool-sequencing approach to better characterize sex-specific markers and sex determination in mandarin fishes. Using genome comparative analysis, we identified significant sex differ-entiated region (-5.0 Mb) and sex chromosome (LG2) in Siniperca chuatsi. Similar sex-differentiated regions were also identified on LG4 in other mandarin fishes including Siniperca knerii, Siniperca scherzeri, and Coreoperca whiteheadi. These non-recombining regions contained high-density of male-biased genetic polymorphisms accompanied with male-biased fragments (-23 kb in total). Meanwhile, sequence synteny analysis showed that whole genomes, including sex chromosomes and even sex-differentiated regions among these species were in good synteny. In addition, the sex-differentiated region harbored 124 genes without "usual suspects" sex determining genes. Based on this genetic information, we successfully developed male-specific genetic markers for mandarin fishes. And genotyping results showed phenotypic sexes were strongly linked to its genetic sexes in one Siniperca chuatsi population. Our results exhibited that sex-differentiated regions and sex chromosomes were relatively conserved in the four mandarin fishes. All the four mandarin fishes were identified to utilize a male heterogametic (XX-XY) sex determination system. Besides, we also developed sex-linked genetic markers. Our study will facilitate future research on sex determination and aquaculture applications in mandarin fishes.