Long-term (5 years) cryopreserved spermatogonia have high capacity to generate functional gametes via interspecies transplantation in salmonids

- Rainbow trout spermatogonia were cryopreserved for up to 5 years.
- Cryopreserved spermatogonia were transplanted into triploid sterile masu salmon.
- Transplanted spermatogonia differentiated into viable sperm and eggs.
- Cryostorage is an effective means to preserve threatened fish spermatogonia.

Although sperm cryopreservation is a powerful tool widely applicable in biodiversity conservation and broodstock management, cryopreservation of teleost eggs and embryos remains challenging. In the present study, we demonstrated that spermatogonia of rainbow trout (Oncorhynchus mykiss) cryopreserved for 5 years possessed the ability to differentiate into functional eggs or sperm in the gonads of triploid recipient masu salmon (Oncorhynchus masou). After cryopreservation for 5 years in liquid nitrogen, intraperitoneally transplanted spermatogonia migrated toward, and incorporated into, the gonads of xenogeneic recipients. The transplanted spermatogonia resumed spermatogenesis and oogenesis in male and female recipients, respectively, and differentiated into sperm or eggs within the gonads of male and female recipients at 2 years posttransplantation. The differentiated sperm and eggs generated normal rainbow trout representative of donor phenotypes. Thus, cryopreservation of spermatogonia is a powerful and reliable method for long-term preservation of fish genetic resources.