Dorsal fin

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.


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

Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать реферат

Look at other dictionaries:

  • dorsal fin(s) — the unpaired fin(s) on the midline of the back. Also called the notopterygium. In Pleuronectiformes it is on the opposite side to the anus. In Centriscidae the hind end of the fish has been rotated under the fish so the dorsal fin is on the under …   Dictionary of ichthyology

  • dorsal fin ray count — enumeration of the soft dorsal fin rays. In fishes where the smaller rays in front gradually grade into larger rays, these smaller anterior rays are included in the count, e.g. Ictaluridae, Esocidae, Gadidae. Where the first small rays abruptly… …   Dictionary of ichthyology

  • dorsal fin base length — the distance between the origin and the insertion of the dorsal fin; the length of that portion of the dorsal fin in contact with the body …   Dictionary of ichthyology

  • dorsal fin — An additional fin surface along the top of the fuse lage just in front of the main fin. Dorsal fins help increase directional stability, especially at high air speeds and Mach numbers …   Aviation dictionary

  • dorsal fin — /ˈdɔsəl fɪn/ (say dawsuhl fin) noun the fin generally developed on the back of aquatic vertebrates …  

  • dorsal fin — noun unpaired median fin on the backs of fishes and some other aquatic vertebrates that help to maintain balance • Hypernyms: ↑fin …   Useful english dictionary

  • dorsal fin — the fin or finlike integumentary expansion generally developed on the back of aquatic vertebrates. See diag. under fish. [1760 70] * * * …   Universalium

  • dorsal fin — noun A fin located on the backs of fish and some marine mammals …   Wiktionary

  • dorsal fin — noun Zoology an unpaired fin on the back of a fish or whale …   English new terms dictionary

  • dorsal fin depressed length — the distance from the origin to the farthest posterior tip when the fin is flattened back down against the body …   Dictionary of ichthyology

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”