Technologies and strategies for ex situ conservation of aquatic organisms: The role of cryopreservation in long-term management

Cryopreservation is a safe method to store and preserve genetic material. Cryobanks in aquatic species were developed with different aims benefiting fish farming, from reproductive management to genetic selection of males with high reproductive value. Research has been conducted on the establishment of protocols for new and problematic species, for commercial or model species, to improve gamete quality during storage or for conservation purposes. Protocols were successfully developed in sperm from several fish and in few invertebrate species as well as in oocytes and larvae, the latter mainly from invertebrates. Identifying the main actors in cryopreservation procedure is a key issue to improve postthaw viability for any biological material. Therefore different methods and approaches have been conducted to determine and reduce cryodamage, identifying the main causes behind it. Each protocol is species specific and depends on the biological material to be preserved, but common aspects need to be taken into account in order to standardize procedures. Another source of cryobanking material is the germ cells. Cryopreserved spermatogonia can be transplanted between closely related species, differentiating into male or female gametes in the host gonads, allowing the preservation of the all-fish genome. Due to this capacity, spermatogonia xenotransplantation using cryopreserved material is becoming a useful tool to produce surrogate broodstocks, particularly in species difficult to maintain in captivity, with high age at maturation or with reproductive problems. In the present chapter, the technologies and approaches allowing the development of a cryopreservation protocol for a given species or cell type will be reviewed and discussed, presenting examples of application in a wide range of fields.