Successful transplantation of cryopreserved spermatogonia in Sebastes schlegelii: A simple and suitable alternative approach for conservation of viviparous fish

Black rockfish ( Sebastes schlegelii ) is one of the most important marine economic viviparous fishes. Recently, germplasm degradation and genetic diversity reduction have occurred due to overfishing and long-term artificial breeding . Germ cell transplantation combined with cryopreservation may be an alternative way to protect genetic resources. However, in viviparous fish that undertake fertilization and embryo development in vivo , transplantation is more difficult than in oviparous fish, including selection of transplantation stage, isolation of germ stem cells , and preparation of sterile recipients. This seriously restricts the development of viviparous transplantation. Therefore, in this study, we aimed to explore a transplantation method suitable for these species. Donor cells were isolated from cryopreserved whole testes of 300–400 ​g male Sebastes schlegelii in May, labeled by PKH26, and intra-peritoneally transplanted into allogeneic larvae at 5–10 days post-birth. Subsequently, the development of donor-derived cells in recipients were continuously detected by fluorescence labeling, histology, microsatellite markers, and fecundity tests. The results showed that donors were rich in spermatogonia (75%) and recipients maintained a high survival rate after transplantation, with a rate of >20% at sexual maturity. Further, donor-derived cells successfully migrated (100%), colonized, and incorporated into the developing recipient gonad (93.33%). Finally, transplanted recipients could normally develop and differentiate into male and female individuals, with donor-derived gametes found in 65.38% of mature recipients. In the present study, we first establish a simple and suitable transplantation method for Sebastes schlegelii using immature males and specific larvae, which will serve as a promising tool in the protection of germplasm resources for this transplantation-restricted marine viviparous species.