Cycloid scales are most often found on advanced fish species, such as trout, herring, and carp. However, fish are not necessarily covered in a single type of scales. Some species, such as flounders, have ctenoid scales on one side of the body and cycloid scales on the other. Scale type can also vary depending on the sex of the fish. The males of certain species may be covered in ctenoid scales, although the females are enveloped in cycloid scales.