Investigation of sex determination in starry flounder ( Platichthys stellatus) reveals sex chromosome evolution in Pleuronectiformes and identifies a sex-specific marker.

The identification of sex chromosomes is fundamental for exploring the mechanism and evolution of sex determination. Platichthys stellatus, a species exhibiting clear sexual dimorphism and homomorphic chromosome pairs, has received limited research concerning its sex determination mechanisms. Clarifying the sex chromosome of P. stellatus will enhance our understanding of sex chromosome evolution in Pleuronectiformes. This study employed whole-genome resequencing to investigate the sex chromosome and sex determination system in P. stellatus. Notably, Chr23 was identified as the sex chromosome in P. stellatus, with the sex-determining region (SDR) occupying 48.1% of the chromosome and featuring an XX/XY system. Sex chromosome turnover was observed within Pleuronectiformes, with P. stellatus, Verasper variegatus, and Hippoglossus hippoglossus sharing a common ancestral karyotype. No inversions were detected within the SDR of P. stellatus, although chromosomal rearrangements between sex chromosomes and autosomes were identified. Additionally, a sex-specific marker for P. stellatus was ascertained, enabling genetic sex identification, with significant implications for improving breeding programs and aquaculture practices.