This is not an aquarium story, but it is about fish, and it is true.
Several years ago I bought a dozen live killes to use as fish bait. I had to cut the fishing short, and still had most of the killies. I brought them home in the bait bucket, drained most of the water, and put the killies and some water in a zip lock bag, which I placed in the freezer. A week later, I took the frozen block of water and killies with me back to the inlet for more fluke (summer flounder) fishing. Before I left the house, I put a few inches of water in the bucket, and put the killies cube into the bucket to melt. About an hour later I arrived at the inlet, and looked in that bucket. I saw a bunch of dead defrosting killies, and one weakly swimming live one.
I honest to God felt my blood run cold. I carried that killy to a shallow part of the bay, and released it. I can't explain how this common Fundulus bait killy survived a week while frozen in a small block of ice, but it did.