Almost all fish have scales. Fish scales are much like the armor that ancient soldiers wore to protect their bodies. When a fish swims, its scales prevent it from doing much damage even if it hits the corners of a rock.

In addition to the protective role of the scales, the fish's skin has a mucus cells, which are very small and can only be seen with a microscope. The mucus cells secrete mucus continuously. After these mucus is spread all over the body, it can reduce the friction of the fish's body in the water, making the fish swim easier and more agile, as well as protecting it from parasites, molds, bacteria and other microorganisms.