I don’t know. Our goldfish and Koi in the pond were covered in a thick sheet of ice except for a small hole and they’re fine now. You could see them perfectly still but for the tip of their tail moving every few seconds.
True story:
Late April, 2012: Went to a stormwater retention pond in SW-Suburban Chicago to pick-off panfish with my fly-rod.
While standing on the bank, I noticed that someone had tossed in some hi-viz traffic control devices; fluorescent-orange pieces.
Until that equipment started to swim away from my casts! Large domestic goldfish had been turned loose in the pond. AFIAK, they survive today.