Sperm cryopreservation in marine mollusk: a review

Sperm cryopreservation is a valuable technique that can enhance the efficiency of genetic improvement programs, commercial production and endangered species conservation. Although studies on sperm cryopreservation in marine mollusks started late in comparison with livestock and finfish, research has substantially increased for the major economical species farmed in the world, including oysters, mussels, scallops, pearl oysters, clams and abalone. In this paper, the latest developments in marine bivalves and gastropods sperm cryopreservation were reviewed and summarized for seven key steps: (1) sperm collection, (2) extender selection, (3) cryoprotectant agent selection, (4) sperm dilution/concentration before cryopreservation, (5) cooling rate, (6) thawing temperature, and (7) quality assessment. In general, the sperm quality is controlled by physiological and environmental parameters and further compromised by the cryopreservation processes. However, less attention has been paid to these issues in sperm cryopreservation in marine bivalves and gastropods. Discussion about factors affecting sperm quality is, therefore, extended to include information from livestock and finfish species where they have been largely evaluated. Knowledge on these factors would not only improve our understanding of the key parameters influencing the success of sperm cryopreservation, but also provide information to develop strategies to improve the sperm quality in marine mollusks.