Types of Fish Scales

Cosmoid scales Cosmoid scales are found in the Lungfishes (family Ceratodidae) and some fossil fishes.

Cycloid and ctenoid scales are derived from ganoid scales that have lost the ganoine and thinned the bony embedded plate. As a fish with cycloid or ctenoid scales grows, its scales also grow. This results in a pattern of concentric growth rings on the scale, which look a little like the growth rings in the trunk of a tree.

Ganoid scales are dimond-shaped scales found in lower order fishes such as the bichirs (Polypteridae), Bowfin (Amia calva), paddlefishes (Polyodontidae), gars (Lepisosteidae), and sturgeons (Acipenseridae).

Placoid scales are the tiny tough scales that cover the skin of sharks, rays, and other elasmobranchs. Even though placoid scales are similar to the scales of bony fish, they are modified teeth and are covered with a hard enamel.