Introduction
Mugil cephalus is a cosmopolitan species valued for its cured roes (bottarga). Its high market value drives the development of aquaculture practices, with the establishment of all-female populations being a key objective.
M. cephalus is gonochoristic species, lacking sexual dimorphism. Dor et al. (2016) identified a sex-determining locus suggesting an XY sex-determination system. Ferraresso et al. (2021) linked this to variants in the follicle-stimulating hormone receptor (fshr) gene, with females being homozygous (wt/wt) and males heterozygous (wt/m1 or wt/m2). However, homozygous (wt/wt) males occur in wild populations. Selecting such genotypes for breeding was proposed as strategy to produce female F1 progeny. Andree et al. (2024) validated a rapid, non-lethal, PCR-RFLP assay for genotyping, enabling early sex identification and broodstock selection. Authors used these tools to genotype male individuals in a captive F1 population showing skewed sex ratios (91.4% female), confirming that all tested males in that population were also homozygous wt/wt.
This study aimed to confirm if 1) wt/wt males can produce viable offspring and 2) the resulting progeny expresses the wt/wt genotype associated with a predominantly female phenotype.
Methods
In August 2025, a wild-caught wt/wt male identified by PCR-RFLP and confirmed by sequencing was selected based on sperm fluency and mated with a female (FAO Fisheries and Aquaculture Technical Papers No. 699). Fertilized eggs were transported to IMC laboratories, where rearing is ongoing. At 80dph animals were genotyped by both PCR-RFLP and sequencing. In October 2026 phenotypic sex of the offspring will be evaluated by histology to associate genotype with phenotype.
Results & Discussion
Progeny genotyping revealed 100% wt/wt genotype. Results of the genotype/phenotype association will be reported. This outcome contributes to a growing body of evidence that an XX/XY sex determination system in Mugil cephalus exists and demonstrates that wt/wt males can successfully be used to produce viable offspring with all female genotype.
References
Andree K.B., Loi B., Vallainc D., Concu D., Duncan N., Carboni S. (2024). Investigation of the utility of PCR-RFLP as a rapid alternative to DNA sequencing for interrogation of the genetic sex of Mugil cephalus. Anim. Reprod. Sci. 270: 107614. DOI: 10.1016/j.anireprosci.2024.107614.
Dor L., Shirak A., Rosenfeld H., Ashkenazi I.M., Band M.R., Korol A., Ronin Y., Seroussi E., Weller J.I. and Ron, M. (2016). Identification of the sex-determining region in flathead grey mullet (Mugil cephalus). Anim. Genet. 47: 698-707. DOI: 10.1111/age.12486
Ferraresso S., Bargelloni L., Babbucci M., Cannas R., Follesa M.C., Carugati L., Melis R., Cau A., Koutrakis M., Sapounidis A., Crosetti D., Patarnello T. (2020). fshr: a fish sex-determining locus shows variable incomplete penetrance across flathead grey mullet populations. iScience 24(1): 101886. DOI: 10.1016/j.isci.2020.101886
Vallainc D., Estevez A., Ramos S.J., Concu D., Carboni S., Duncan N. & Lovatelli, A. (2026). Hatchery, nursery and grow-out techniques for the flathead grey mullet (Mugil cephalus). FAO Fisheries and Aquaculture Technical Papers, No. 699. Rome, FAO, 182 pp. DOI: 10.4060/ cd9536en