Ctenoid scales are scales with comb-like edge found in higher order teleost fishes, such as perch and sunfish. Cteni are the tiny teeth on the posterior margin of the scale. Similar to cycloid scales, they are overlapping which allows 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.