As a new freshwater aquaculture product, triploid loaches (Misgurnus anguillicaudatus) are characterized by fast growth, high-quality meat, high edibility, high resistance to disease, and sterility. In this study, a natural tetraploid loach (4n = 100) (♀) was crossed with a diploid loach (2n = 50) (♂), thus creating the hybrid triploid loach (3n = 75). The histological observations of triploid offspring and diploid controls at 4 days post-hatching (dph), 15dph, 22dph, and 50dph showed that most of the hybrid triploid loaches were abortive in the early gonad differentiation process. To explore its fertility mechanism, through transcriptome analyses of triploid offspring and diploid controls at four periods, 10 differentially expressed genes related to the early fertility mechanism were identified: amh, hormad1, rec8, h2b, plvap, zp3, h2a, nrb0b1, ddx4, and esr2. According to the Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses of DEGs, two pathways were identified that are closely related to the early fertility mechanism at 50dph: the estrogen signaling pathway and steroid biosynthesis. The findings laid a foundation for further exploration of their molecular inhibition mechanism in hybrid triploid loaches.

As an important aquaculture fish, the genus Carassius exhibits different ploidy, including tetraploids and hexaploids