Operculum (fish)

The Operculum is a series of bones found in bony fish that serves as a facial support structure and a protective covering for the gills; it is also used for respiration and feeding.

The opercular series contains four bone segments known as the pre-operculum, suboperculum, interoperculum and operculum. The pre-operculum is a crescent-shaped structure that has a series of ridges directed posterodorsally to the organisms canal pores. The pre-operculum can be located through an exposed condyle that is located immediately under it's ventral margin; it also borders the operculum, suboperculum, and interoperculum posteriorly.

Please see Anatomical terms of location as a reference for anatomical location terminology (This section is still under development).

For some fish, opercula are vital in obtaining oxygen. They open as the mouth closes, causing the pressure inside the fish to drop. Water then flows towards the lower pressure across the fish's gill lamellae, allowing some oxygen to be absorbed from the water.

Whereas the cartilaginous ratfishes have soft and flexible opercular flaps, the sharks, rays and relatives (elasmobranch fishes) lack opercula completely and respire instead through a series of gill slits perforating the body wall. Without opercula, other methods of getting water to the gills are required, such as ventilation.

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