Structure of Scales

• In most fishes, the skin covered with an exoskeleton in the form of scales and few are naked having no scales on their body as the cat fishes.
• The scales have been divided into two basic types; placoid and nonplacoid.
• The former divided from epidermis and dermis but non-placoid scales are derived from the dermis.
• The non-placoid scales are basically of three types: bony ridge (cycloid and ctenoid), cosmoid and ganoid types of scales.