Goldfish scales lifted due to warm water
Goldfish scales lifted due to warm water or fever. Fish raise their scales in an effort to cool their body temperature. Having no core body temperature, goldfish cannot endure high measures of heat. Most freshwater fish are cold blooded, like goldfish, and require regulated temperatures. The comfort zone for goldfish is 64f to 74f, however, they can tolerate much lower levels above freezing
Our goldfish fare much better in ponds if the bottom is dug down to the freeze line. There is no better insulator than earth. You may live in a region with a shallow freeze line, meaning it gets very cold. Regions such as Alaska have zero freeze line, meaning the earth is frozen in the extreme of winter no matter how deep you dig. Some regions have no freeze line, meaning it never freezes. Pond bottoms should be just below the freeze line of your region