Cryopreservation of eggs and sperm is known as a method of permanent preservation of endangered species and genetically modified animals.However, since fish eggs are large in size and rich in fat, the development of technology for cryopreserving eggs and embryos as they are has not progressed.

　The research group soaked the entire medaka testis in a cryoprotective solution and then frozen it in liquid nitrogen at -196 ° C.After thawing them, the survival of the cells was analyzed, and it was found that spermatogonia can be obtained with good reproducibility even if they are cryopreserved for one year.Furthermore, by transplanting these cells into the surrogate parent medaka larvae immediately after hatching, functional sperm derived from the frozen testis when the surrogate parent is a male and functional eggs derived from the frozen testis when the surrogate parent is a female. Was able to produce.In addition, by mating these surrogate parents, we succeeded in producing the next generation derived from spermatogonia in the frozen testis.

　This time, we used the endangered "Tokyo Medaka" and the male Dharma medaka, which has a small number of eggs.By cryopreserving these testes and transplanting the obtained spermatogonia to the surrogate parent, Himedaka, we succeeded in obtaining "Tokyo Medaka" and Dharma Medaka from Himedaka, which has a large number of eggs.

　Inbreeding and wild strains that are useful for research had no other way to preserve them than to keep them, but the development of this technology has made it possible to cryopreserve those medaka genetic resources semi-permanently.

Paper information: [Scientific Reports]Production of the medaka derived from vitrified whole tests by germ cell transplantation