Both cycloid and ctenoid scales consist of a rigid surface layer primarily composed of calcium-based salts and a fibrous inner layer that is mainly made of collagen. The primary difference between the two types of scales is their fundamental shape. Cycloid scales exhibit a smoothly rounded posterior edge, whereas those of the ctenoid variety are characterized by a row of comb-like extensions. Both types line the skin in an overlapping design, but are generally associated with different aquatic species. Cycloid scales are most often found on carps and similar fishes, while ctenoid scales are more common to higher bony fishes, including perch and sunfish.