Successful cryopreservation of spermatogonia in critically endangered Manchurian trout (Brachymystax lenok)

Because of the lack of cryopreservation techniques for fish eggs and embryos, cryopreservation of fish spermatogonia and subsequent generation of eggs and sperm would be an exit strategy for the long-term preservation of genetic resources. This study aimed to optimize cryoprotectants, cooling rates, and thawing temperatures for slow freezing of spermatogonia from endangered Manchurian trout (Brachymystax lenok). Whole testes were frozen with a cryomedium containing 1.3 M methanol, 0.2 M trehalose, and 10% egg yolk at a cooling rate of −1 °C/min and then stored in liquid nitrogen for 2 days. After thawing at 30 °C in a water bath, testicular cells from thawed testes were intraperitoneally transplanted into allogeneic triploid hatchlings. Transplanted spermatogonia migrated toward and were incorporated into recipient gonads, where they underwent gametogenesis. Transplantation efficiency did not significantly differ between frozen and fresh testes, demonstrating that Manchurian trout spermatogonia can be successfully cryopreserved in liquid nitrogen.