Oysters and mussels are among the most farmed species in aquaculture industry around the world. The aim of this study was to test the toxicity of cryoprotective agents to trochophore larvae from two different species of bivalves and develop an improved cryopreservation protocol to ensure greater efficiency in the development of cryopreserved trochophores (14h old oyster larvae and 20h old mussel larvae) to normal D-larvae for future developments of hatchery spat production. The cryopreservation protocol producing the best results for oyster trochophores (60.0±6.7% normal D-larvae) was obtained by holding at 0°C for 5min then cooling at 1°Cmin−1 to −10°C and holding for 5min before cooling at 0.5°C to −35°C, holding 5min and then plunging into liquid nitrogen (LN), using 10% ethylene glycol. For mussel experiments, no significant differences were found when cooling at 0.5°Cmin−1 or at 1°Cmin−1 for CPA combinations with 10% ethylene glycol and at 0.5°Cmin−1. Using these combinations, around half of trochophores were able to develop to normal D-larvae post-thawing (48.9±7.6% normal D-larvae).