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EveryFish

Dorsal fin

The fin on a fish's back, which keeps it upright and stops it rolling as it swims.

A diagram drawn by EveryFish.

Also: back fin

The dorsal fin rises from the midline of the back. It works like the keel of a boat turned upside down, keeping the fish steady and helping it turn sharply. Many fish have one dorsal fin; cod have three, and perches have two, a front one stiffened by sharp spines and a rear one of soft rays. In sharks the tall triangular dorsal fin is the one seen cutting the surface. In some fish it has other jobs: the anglerfish's lure is a dorsal spine moved to the snout, and the sailfish raises its huge dorsal fin to herd prey.

See also

Fin rays and spines Pectoral fin Caudal fin Adipose fin

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