As a kid I retrieved some spawn from a village pond that had a fair bit of ice, though it wasn't frozen solid, and the spawn proved viable. All I had done was stick the spawn in an old hand basin of ditchwater in an unheated room. The youngsters did not survive the DDT treatment of the old upholstered chair that was being restored close by, but they had reached the beginning-to-hop stage by then. Mum still has the chair nearly 50 years later.

I wonder how hard the stuff can be frozen before it is damaged. Maybe it is frost-proof, given that sperm, embryos (& eggs?) are regularly deep-frozen in connection with AI and IVF work.