Dorsal fin

Dorsal fin of an Orca

A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals (whales, dolphins, and porpoises), and the (extinct) ichthyosaurs. Depending on the species, an animal can have up to three of them.

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

The bones or cartilages that support the dorsal fin are called pterygiophores.

The dorsal fin is probably best known as the visible sign of an approaching shark.

Functions

Dorsal fin of a shark

The main purpose of the dorsal fin is to stabilize the animal against rolling and to assist in sudden turns. Some species have further adapted their dorsal fins to other uses. The sunfish uses the dorsal fin (and the anal fin) for propulsion. In anglerfish, the anterior of the dorsal fin is modified into a biological equivalent to a fishing pole and a lure known as illicium or esca. 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. In the case of the electric eel, the role of the dorsal fin is taken by an anal fin.

See also

• Fish anatomy