**1. Introduction**

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Diploidic germplasms such as embryos, compared to haploidic gametes, are theoretically a better choice for preservation of an animal species. However, there are significant challenges in cryopreservation of multicellular materials due to their size and physical complexity which affect the permeation of cryoprotectants and water, sensitivity to chilling and toxicity of cryoprotectants. While cryopreservation technologies are well developed and found feasible in embryos/larvae of some species, embryos of other species such as zebrafish failed to be cryopreserved. In addition, cryopreservation in many other emerging model organisms have not been developed at all. Hence, the limited cryopreservation technology has become a bottleneck in the development of various research areas, especially those relying on molecular genetics of emerging model organisms. Thorough understanding of the embryonic development and critical stages tolerant to cryopreservation needs to be identified so as to facilitate expansion of model systems available for specific biological and experimental interrogations.
