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EveryFish

Gills

The feathery organs behind the head where a fish takes oxygen from water and gives off carbon dioxide.

A diagram drawn by EveryFish.

Also: gill arches, gill filaments

Water comes in through the mouth, passes over the gills and leaves through the gill openings. Each gill is a bony arch carrying rows of thin filaments, which are folded again into tiny plates packed with blood vessels. Blood in the plates flows the opposite way to the water, a countercurrent that lets a fish take most of the oxygen out of the water. Bony fish have four gill arches on each side under a cover, the operculum. Sharks and rays have five to seven open gill slits. Bright red gills are one sign of a fresh fish at the market.

See also

Operculum Gill rakers Spiracle Labyrinth organ

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