Constructing High-Density Genetic Maps and Developing Sexing Markers in Northern Snakehead (Channa argus).

High-density genetic maps are essential for mapping QTL, improving genome assembly, comparative genomics, and studying sex chromosome evolution. The northern snakehead (Channa argus) is an economically important foodfish species with significant sexual dimorphism, where the males grow much faster and bigger than the females. However, to date, the sex determination pattern is still not clear, limiting identification of sex chromosomes, even sex determination genes and development of monosex populations that are valuable for both sex evolution of vertebrates and aquaculture practices. Here, a sex-averaged map and two sex-specific genetic maps were constructed with 2974, 2323, and 2338 SNPs, respectively. Little difference was observed in the pattern of sex-specific recombination between female- and male-specific genetic maps. Genome scan identified a major locus for sex determination at LG16. Females and males are, respectively, homogametic and heterogametic, suggesting an XY sex determination system for this species. By resequencing genomes, InDels in the sex-associated QTL region were discovered and used for developing sex-specific PCR assays for fast sexing of snakehead. These high-density genetic maps provide useful resources for future genomic studies in snakehead and its related species. The PCR assays for sexing are of importance in developing all male populations for aquaculture.