dorsal fin

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Dorsal fin of an Orca

A dorsal fin is a fin located on the backs of some fish, whales, dolphins, and porpoises, as well as the (extinct) ichthyosaurs. Depending on the species, an animal can have up to three of them. Its main purpose is to stabilize the animal against rolling and assist in sudden turns. The bones that support the dorsal fin are called Pterygiophore.

They are infamous for being the sign of an approaching shark.

Functions

Dorsal fin of a shark

Though the primary use of the dorsal fin in most animals is to protect the fish against rolling, and assists in sudden turns and stops, some species have adapted their dorsal fins to other uses. In anglerfish, the anterior of the dorsal fin is modified into an illicium and esca, a biological equivalent to a fishing pole and a lure. Many catfish can lock the leading ray of the dorsal fin in an extended position to discourage predation or to wedge themselves into a crevice. Some animals have developed dorsal fins with protective functions, such as spines or venom. For example, both the Spiny Dogfish and the Port Jackson shark have spines in their dorsal fins which are capable of secreting poison.

Wildlife biologists often use the the distinctive nicks and wear patterns which develop on the dorsal fins of large animals, especially whales, to identify individuals in the field.

See also

• Fish anatomy

Notes

References