Sperm cryopreservation in oysters: A review of its current status and potentials for future application in aquaculture

• Cryopreservation can assist genetic improvement programs.
• Applications of cryopreserved sperm in oyster aquaculture are explored.
• Recent research progresses of sperm cryopreservation in oysters are reviewed.
• Quality insurance of cryopreserved sperm is needed for successful breeding programs.

Cryopreservation has been expected to improve the efficiency of hatchery operation by supplying gametes on demand without live broodstocks and genetic improvement programs by achieving desired mating and establishing across-generation controls. The preservation of genetic materials of improved stocks and the original population is immensely important for oyster aquaculture industry to prepare the potential impacts from epidemic diseases and natural disasters. This review summarizes the research progress of sperm cryopreservation in oysters and discusses the scope of application of preserved sperm in aquaculture. A bulk of about 50 reports have been published on oyster sperm cryopreservation since 1971, nevertheless the application of this technique in aquaculture is limited. These studies primarily focused on the development of protocol for individual species by optimizing a set of interacting variables at different steps from sperm collection to post-thawing and fertilization. A number of approaches such as sperm motility, morphological integrity and fertility are used to evaluate the cryopreserved sperm quality but there are considerable variations in practice. We synthesized the outcomes in the existing literature in an attempt to suggest the standardization of sperm cryopreservation technique and provide directions for future research.