Cycloid scales are smooth-edged scales predominately found in lower order teleost fishes, such as salmon, carp and other soft fin rayed fish. Similar to ctenoid scales, they are overlapping which allow for greater flexibility in movement than other types of scales such as ganoid scales. The surface layer of the scale is comprised of calcium-based salts and the inner layer is predominately collagen. As a fish grows, its scales grow, adding concentric layers, similar to tree rings. For certain species, these rings can be counted to estimate the age of a fish.