[*Ci*]

Oh, I was told by my local vet that freezing the really any small animal (such as mouse, rat or even fish) was humane because they would just be cold for a minute or so and then fall asleep, and die.

Since fish are cold blooded, it is a natural function to sink into torpor as the temperature drops. I don’t believe they would feel discomfort if frozen, although a mammal most certainly would.