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EveryFish

Operculum

The bony flap that covers and protects the gills of a bony fish.

Also: gill cover

The operculum is the hard gill cover on each side of a bony fish's head, made of a few flat bones joined together. As the fish opens its mouth, the operculum closes, and as the mouth closes, the operculum swings out, pumping water over the gills even when the fish is still. Sharks and rays have no operculum; many sharks must keep swimming, or pump water with their mouths, to breathe. The pattern and spines of the operculum help identify some groups, such as groupers and croakers.

See also

Gills Bony fish Cartilaginous fish

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