Production of common carp donor-derived offspring from goldfish surrogate broodstock

Common carp (Cyprinus carpio) is the fourth most-produced species in worldwide aquaculture. Significant efforts are invested in breeding and preservation of genetic integrity of this important species. However, maintaining a carp gene bank in situ can be demanding due to the large body size of the fish. Moreover, ex situ gene banking in common carp is as in other fish species limited to sperm cryopreservation. Recent progress in reproductive biotechnology in fishes has allowed the transfer of germ stem cells (gamete precursors) between individuals or even species. After maturation, the recipients are producing gametes of the donor. Surrogacy can serve as a valuable tool in germplasm banking to recover cryopreserved germ stem cells. Some unfavourable characteristics of the donor species such as long maturation time or large body size hampering its reproduction can be overcome by choosing a surrogate with more convenient characteristics. Efficient protocols for cryopreservation of common carp male and female germ stem cells have been recently developed in our laboratory. The next step has been to assess the potential of smaller goldfish (Carassius auratus) surrogates to produce donor-derived gametes of common carp after intraperitoneal transplantation of testicular cells. High transplantation success was achieved when 44% of the surviving goldfish produced pure donor-derived gametes of common carp at the age of 3 years giving rise to viable progeny. Donor-derived identity of the offspring was confirmed by genotyping and the production of a typical phenotype corresponding to the donor species. Reproductive performance of chimeras was similar to goldfish controls. Assessment of gamete characteristics showed that the size of donor-derived eggs is between control common carp and goldfish eggs. Interestingly, flagellum length in donor-derived spermatozoa was comparable to the common carp flagellum and significantly shorter than goldfish flagellum. Genotyping of the Y chromosome locus in chimeric goldfish provided a novel insight on the fate of transplanted cells, where only genotypic females were capable of producing eggs, while both genotypic males and females were capable of producing sperm. The present technology can be combined with cryopreservation procedures to ease needs for common carp breeds preservation and their recovery using many times smaller goldfish surrogates but also serve as a convenient model to study interspecific surrogacy in cyprinids.