Effect of the cryoprotectants glycerol, ethylene glycol and acetamide on the hatching rate of common carp (Cyprinus carpio) embryos

Fish embryo cryopreservation means substantiation of the body water with a cryoprotectant. Knowledge of cryoprotectants toxicity is one of the prerequisites for the design of embryo cryopreservation protocols. In the present study common carps (Cyprinus carpio) in two stages of embryonic development, half-epiboly (8 h post-fertilization) and heartbeat (32 h post-fertilization) stage, were exposed to pronase, type XIV of Streptomyces griseus, for 5 min. Permeabilized embryos were immersed in various cryoprotectants including glycerol, ethylene glycol and acetamide in concentrations of 1, 2, 3 and 4M for a period of 5 and 15min. Embryos were then washed and incubated until hatched. The toxicity of the cryoprotectant was assessed by the hatching rate. The results indicated that glycerol had less toxicity compared to ethylene glycol and acetamide. Moreover, embryos could tolerate glycerol in high concentrations. Acetamide was found to be the most toxic cryoprotectant. Reduced hatching rate may be a result of osmotic shock, ionic imbalance or consequence of cryoprotectant toxicity. As concentrations were increased, hatching rate decreased. Similarly, hatching rates of embryos were decreased as the exposure time increased (5 to 15 min). With the increasing of the embryonic development sensitivity to cryoprotectant were decreased. Results suggest that glycerol and ethylene glycol would be good options for cryopreservation of common carp embryos at heartbeat stage.