2001 Volume 47 Issue 2 Pages 69-74
The cold tolerance and ice nucleation temperature of medaka embryos in three embryonic stages were investigated with different cryoprotectant treatments. The ice nucleation temperatures of the embryos in every stage showed a decreasing tendency by cryoprotectant treatment, in the order of trehalose, DMSO, and a combination of trehalose and DMSO. Further, the ice nucleation temperatures of the control embryos were depressed with the embryonic development. However, when the embryos were treated with the cryoprotectants, the stage dependency on the ice nucleation temperatures could not be recognized for 8 cell and optic bud stages, and only at the eyed stage the ice nucleation temperatures were significantly lower than those in early embryonic stages. On the other hand, the cold tolerance of the embryo at a temperature below 4℃, which was examined at the temperature range without occurrence of ice nucleation, became higher in every stage by cryoprotectant treatments. As for the stage dependency, it could be found that the cold tolerance of the embryos treated with cryoprotectants did not show a large difference among the stages, however, in the case of control embryo the cold tolerance at the exposure temperature below 4℃ showed an increasing tendency as the stage developed. As the conclusion, it was suggested that the lowering of the ice nucleation temperature of the embryos led to the increase in the survival rate of embryos at the cold temperature without ice nucleation, although other factors such as the development stage should be considered in.
