Why certain fish liquify when cooked.
Actually, it doesn't have anything to do with the way it was frozen or thawed. When a fish like black cod stays too
long on the hook after being caught, it sometimes drowns before being fished out of the water. The body of the fish then fills with water. It's hard to tell until you actually cook it. But if it is the case, a nice looking filet will start to turn to fish soup after a few minutes in the oven or in the pan.
It happened to me tonight. That's the explanation I got from the fishmonger along with my money back:)