Why do some fish have scales and others not?
It all goes back to evolution. Some fish do not require scales like sharks. Most of it boils down to where the fish lives salt or fresh, rocks or sand and how many other fish there are that will have him for lunch. That isn’t always true however. The skin of many fish is covered with scales that protect a fish like roof shingles protect a house. You could also compare the covering of scales to a suit of armor. A fish only develops scales during its first year of life. As fish grow, their scales get bigger. Fish growth, and scale growth, slows in the winter and speeds up in the summer. The alternating periods of growth form rings on a scale just as they do in tree trunks. It’s possible to examine these rings under a magnifying lens to see how old a fish is. All fish have body slime. The species with less well developed scales or no scales at all tend to have more slime. The slime reduces drag to help a fish move faster in the water. It also provides protection against parasites, covers
