Identification of sex determination mechanism in Starry Flounder (Platichthys stellatus) provides sex chromosome evolution among Pleuronectiformes and indicates the sex-specific marker.

Sex chromosome is fundamental for exploring sex determination mechanism and evolution. Platichthys stellatus exhibits clear sexual dimorphism and features homomorphic chromosome pairs. Given the limited research on the sex determination mechanism of P. stellatus, identifying its sex chromosome is of great importance to understanding the evolutionary mechanism of sex chromosomes in Pleuronectiformes. Therefore, we used whole-genome resequencing data to identify the sex chromosome and sex determination system of P. stellatus. In our study, we identified that Chr23 of P. stellatus is sex chromosome. The sex determination region (SDR) occupies 48.1% of the sex chromosome, featuring an XX/XY sex chromosome type. Sex chromosome turnover has been observed in the Pleuronectiformes and P. stellatus, Verasper variegatus and Hippoglossus hippoglossus share the same ancestral karyotype of sex chromosome. Within the SDR of P. stellatus, no inversions were detected. Rearrangements occur between sex chromosome and autosome. Additionally, we developed a sex-specific marker for P. stellatus, which could be used to distinguish its genetic sex, offering significant implications in the development of breeding strategies and aquaculture industries.