Conservation of coral reef fishes: a field-hardy method to cryopreserve spermatogonial cells

The biodiversity of marine fishes is threatened globally by climate change and other anthropogenic activities, particularly in coral reef ecosystems. We present a simple, field-hardy method to cryopreserve marine fish gonads, targeting spermatogonial cells (undifferentiated diploid germ cells) with the ultimate goal of permitting recovery of threatened species and populations via gonadal diploid germ cell transplantation technologies. The use of a simplified cryopreservation extender based on L-15 medium resulted in minimal decline in spermatogonial cell viability post-thaw. Moreover, we compared post-cryopreservation viability of sperm and spermatogonial cells from gonads cryopreserved with freshly prepared cryoprotectant and with cryoprotectant prepared in advance and stored at −20 °C. We found no significant difference, suggesting that these solutions may be prepared in advance and frozen, ready for later use. We urge conservation, academic, and regulatory agencies to cryobank fish gonads as part of their sample collection processes to support the biodiversity and security of valuable marine fish resources, alongside other restoration efforts.