Adorsal fin is afin on the back of most marine and freshwatervertebrates. Dorsal fins have evolved independently several times throughconvergent evolution adapting tomarine environments, so the fins are not allhomologous. They are found in mostfish, in mammals such aswhales, and in extinct ancientmarine reptiles such asichthyosaurs. Most have only one dorsal fin, but some have two or three.
Wildlifebiologists often use the distinctive nicks and wear patterns which develop on the dorsal fins of whales to identify individuals in the field.
The bones or cartilages that support the dorsal fin in fish are called pterygiophores.
The main purpose of the dorsal fin is usually to stabilize the animal against rolling and to assist in sudden turns. Some species have further adapted their dorsal fins to other uses. Thesunfish uses the dorsal fin (and theanal fin) for propulsion. Inanglerfish, the anterior of the dorsal fin is modified into a biological equivalent to a fishing pole and a lure known as anillicium oresca.
Some fishes have adapted their dorsal fins todefend against predators with sharp erect spines and venom, as in many species ofcatfish,[1] thespiny dogfish,[2] and perhaps thePort Jackson shark,[3]
Billfish have prominent dorsal fins. Like tuna, mackerel and other scombroids, billfish streamline themselves by retracting their dorsal fins into a groove in their body when they swim.[4] The shape, size, position and colour of the dorsal fin varies with the type of billfish, and can be a simple way to identify a billfish species. For example, the white marlin has a dorsal fin with a curved front edge and is covered with black spots.[4] The huge dorsal fin, or sail, of thesailfish is kept retracted most of the time. Sailfish raise them if they want to herd a school of small fish, and after periods of high activity, presumably to cool down.[4][5] Thegreat white shark's dorsal fin contains stabilizingdermal fibers that stiffen dynamically as it swims faster, helping it to control roll and yaw.[6]
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A dorsal fin is amedial, unpaired fin that is located on the midline of the backs of some aquatic vertebrates. In development of the embryo inteleost fish, the dorsal fin arises from sections of the skin that form a caudal fin fold.[7] The larval development and formation of the skeleton that support the median fins in adults result in pterygiophores. The skeletal elements of the pterygiophore includes basals and radials. The basals are located at the base of the dorsal fin, and are closest to the body. The radials extend outward from the body to support the rest of the fin.[7] These elements serve as attachment sites forepaxial muscles.[8] The muscles contract and pull against the basals of the pterygiophores along one side of the body, which helps the fish move through water by providing greater stability.[8] In these types of fish, the fins are made of two main components.[8] The first component is the dermal fin rays known aslepidotrichia, and theendoskeletal base with associated muscles for movement is the second.[7]
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