Selection of cryoprotectants based on their toxic effects on oyster gametes and embryos

Cryopreservation is a valuable tool for aquaculture by providing continuous seed production, regardless of the spawning seasons. This study aimed to select the least toxic among the cryoprotectants dimethyl sulfoxide (Me2SO), propylene glycol (PG), and methanol (MET) based on their toxicological effects on Crassostrea rhizophorae gametes and trochophores. They were exposed for 10, 20, and 30 min to a range of concentrations of those cryoprotectants. The endpoint was EC15-24 h (effective concentration which causes abnormalities in 15% of the population exposed to the cryoprotectants for 24 h), recently determined as the chronic value (the concentration at which chronic effects are first observed) for C. rhizophorae embryonic phases. There were no significant differences (p>0.05) among the exposure times in Me2SO toxic effects to either gametes or trochophores. For MET, the increase in exposure time resulted in higher toxicity for gametes, but not for trochophores, while for PG there was a significant (p>0.05) increase in toxicity with the increase of exposure for trochophores and spermatozoa, but not for oocytes. For gametes, MET was the most toxic among the cryoprotectants, while PG was the most toxic for trochophores.