Ctenoid means 'having the margin toothed like a comb'. It is used to the scales of some fishes, such as perciforms that have such a toothed margin. Ctenoid scales are essentially cycloid scales with teeth at their posterior edges. It is thought that these teeth help to reduce hydrodynamic drag during swimming. Ctenoid scales are found in many teleosts. Fish with ctenoid scales feel rough if rubbed or stroked from tail to head.