Development of a programmable freezing technique on larval cryopreservation in the Pacific oyster Crassostrea gigas

Abstract This study investigated three vital factors to develop a programmable cryopreservation technique for the larvae of Pacific oyster Crassostrea gigas, namely (1) larval developmental stages; (2) cryoprotectant agents (CPAs) and (3) larval density. The D-larval rate was used as the post-thaw survival indicator, which was calculated as the percentage of larvae that develop into D-larvae after 24 h post-fertilization. The results showed that the post-thaw D-larval rate above 80% was achieved when the 18 h post-fertilization (PF) larvae were cryopreserved with the CPA consisting of 10% ethylene glycol +5% Ficoll +0.2% polyvinylpyrrolidone. No significant difference in the rate of post-thaw D-larvae (P > .05) was found between initial larval density of 4 × 105 mL−1 and 1 × 106 mL−1. The shell length of progenies produced from fresh and cryopreserved larvae had no significant difference at all developmental stages investigated. In addition, similar relative mortality rates were found from umbo larvae (day 8 PF) to spat (day 27 PF) between progenies produced from fresh and cryopreserved larvae. Therefore, the larval cryopreservation technique developed in this study could be used to facilitate breeding programs and hatchery management in Pacific oyster aquaculture industry.