I've my Amanos live in water with a layer of ice over it. Not good for them, I suppose, but they lived through it. Thats what I get for not having my heater running and an outdoor tank. Surprisingly though, when moving, it only got down to 40*f and that said amano (along with all my other fish
) died. Then again, it could have just been the stress of moving from one side of the country to the other.