Toxicity of some permeable and non-permeable cryoprotectants on common carp (Cyprinus carpio) embryos

Knowledge of cryoprotectants toxicity is one of the prerequisites for the design of fish embryo cryopreservation protocols. In order to study the effects of cryoprotectants toxicity, common carp (Cyprinus carpio) embryos at half-epiboly and heartbeat stages were selected and exposed to pronase E, type XIV of Streptomyces griseus, (2 mg/ml in Ringer solution) for 5 min. Permeabilized embryos were immersed in: three permeable cryoprotectants, dimethyl sulfoxide (DMSO), methanol (MeOH) and propylene glycol (PG) in concentrations ranging from 1 to 4 M; and one non-permeable cryoprotectant, sucrose (in concentrations of 10%, 15% and 20%) for 5 and 15 min. After these treatments, the embryos were washed and incubated until hatched. The toxicity of the cryoprotectant was assessed by the hatching rate. The results showed that there was a significant decrease of hatching rate in both developmental stages with increased concentration and duration of exposure. In addition, MeOH was the least toxic permeable cryoprotectant, followed by PG and DMSO. Prolonged exposure to sucrose significantly reduced hatching rate, especially at the heartbeat stage. With the increasing of the embryonic development (from half-epiboly to heartbeat stage) sensitivity to cryoprotectants were decreased.