Influences of Developmental Stages, Protective Additives and Concentrations of Cryoprotective Agents on the Cryopreservation of Pacific Oyster (Crassostrea Gigas) Larvae

BACKGROUND: The selection of the optimal developmental stage, appropriate cryoprotectants (CPAs) and their concentrations is important for successful cryopreservation. OBJECTIVE: To investigate the effects of developmental stage and CPA concentrations on the cryopreservation of Pacific oyster (Crassostrea gigas) larvae. MATERIALS AND METHODS: Seven developmental stages, various CPAs and concentrations were investigated for optimizing cryopreservation of Pacific oyster larvae. The morphologies of pre-frozen and frozen-thawed larvae were evaluated using scanning electron microscopy and transmission electron microscopy. RESULTS: The survival rate of frozen-thawed larvae increased with developmental stage; late umbo veligers exhibited a survival as high as 98.6%. The addition of 0.2M or 0.5M sucrose improved the survival of larvae, and 2.0M ethylene glycol (EG) positively influenced the survival of frozen-thawed larvae. Moreover, the frozen-thawed larvae possessed irregularly arranged cilia and displayed a rough surface shell and a round-lumped cilium head. CONCLUSION: The findings indicate that the most desirable cryopreservation of Pacific oyster larvae may occur at any developmental stage except for the early trochophore stage. Sucrose at 0.2M or 0.5M and EG at 2.0M or 2.5M are appropriate cryoprotectant additives.