Development of a saline-tolerant YY supermale UPV SpiN tilapia hybrid (Oreochromis spilurus × O. niloticus) (Actinopterygii, Cichliformes, Cichlidae) using molecular marker-assisted selection

The tilapia aquaculture industry faces increasing challenges from saline intrusion into freshwater systems and consumer concerns over hormone-treated fish. This study developed a molecular marker-assisted YY male technology in the saline-tolerant UPV SpiN tilapia hybrid { Oreochromis spilurus (Günther, 1894) × Oreochromis niloticus (Linnaeus, 1758)} to enable all-male progeny production without direct hormone treatment. A primer set (UPV-SpiN-M5) targeting the amhy gene, a key determinant of male sex differentiation, was utilized. Crosses between neofemales (sex-reversed XY females; XY ♀) and natural XY males produced YY supermales, and mating these with natural XX females yielded 100% genotypically male fingerlings all exhibiting the Y-specific band (~523 bp). Despite the limited number of successful spawns among YY supermale × XX female crosses, the successful families produced viable all-male fry, demonstrating the effectiveness of the molecular-assisted approach. These results demonstrate the feasibility of hormone-reduced monosex production in saline-tolerant tilapia and provide a foundation for scalable, sustainable seed production systems suitable for both freshwater and brackish water aquaculture. Future studies should focus on refining broodstock management to improve spawning success, validate genotypic and phenotypic sex at maturity, assess growth and economic performance of YY-derived males, and explore the use of pseudofemales (sex-reversed YY females; YY ♀) to enable the mass production of YY supermales and enhance overall production efficiency.