Dorsal Fin
   HOME

TheInfoList



OR:

A dorsal fin is a fin on the back of most marine and freshwater
vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...
s. Dorsal fins have evolved independently several times through
convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last comm ...
adapting to marine environments, so the fins are not all homologous. They are found in most
fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...
, in mammals such as
whale Whales are a widely distributed and diverse group of fully Aquatic animal, aquatic placental mammal, placental marine mammals. As an informal and Colloquialism, colloquial grouping, they correspond to large members of the infraorder Cetacea ...
s, and in extinct ancient marine reptiles such as ichthyosaurs. Most have only one dorsal fin, but some have two or three. Wildlife
biologist A biologist is a scientist who conducts research in biology. Biologists are interested in studying life on Earth, whether it is an individual Cell (biology), cell, a multicellular organism, or a Community (ecology), community of Biological inter ...
s 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.


Functions

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. The sunfish uses the dorsal fin (and the
anal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported o ...
) for propulsion. In
anglerfish The anglerfish are ray-finned fish in the order Lophiiformes (). Both the order's common name, common and scientific name comes from the characteristic mode of predation, in which a modified dorsal Fish fin#Ray-fins, fin ray acts as a Aggressiv ...
, the anterior of the dorsal fin is modified into a biological equivalent to a fishing pole and a lure known as an ''illicium'' or ''esca''. Some fishes have adapted their dorsal fins to defend against predators with sharp erect spines and venom, as in many species of
catfish Catfish (or catfishes; order (biology), order Siluriformes or Nematognathi) are a diverse group of ray-finned fish. Catfish are common name, named for their prominent barbel (anatomy), barbels, which resemble a cat's whiskers, though not ...
, the spiny dogfish, and perhaps the Port Jackson shark, File:Carassius wild golden fish 2013 G1.jpg, Most fish, like this large
goldfish The goldfish (''Carassius auratus'') is a freshwater fish in the family Cyprinidae of the order Cypriniformes. It is commonly kept as a pet in indoor aquariums, and is one of the most popular aquarium fish. Goldfish released into the w ...
, have one dorsal fin. File:Parts of a shark.svg,
Shark Sharks are a group of elasmobranch cartilaginous fish characterized by a ribless endoskeleton, dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to the head. Modern sharks are classified within the ...
s typically have two. File:Thunnus albacares.png, The
yellowfin tuna The yellowfin tuna (''Thunnus albacares'') is a species of tuna found in pelagic waters of tropical and subtropical oceans worldwide. Yellowfin is often marketed as ahi, from the Hawaiian , a name also used there for the closely related bigeye ...
has two. File:Haddock fins.tiff, Haddocks have three.
Billfish The billfish are a group (Xiphioidea) of saltwater fish, saltwater predatory fish characterised by prominent pointed beak, bills (rostrum (anatomy), rostra), and by their large size; some are longer than . Extant billfish include sailfish and m ...
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. 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. The huge dorsal fin, or sail, of the sailfish 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.''Aquatic Life of the World''
pp. 332–333, Marshall Cavendish Corporation, 2000. .
The
great white shark The great white shark (''Carcharodon carcharias''), also known as the white shark, white pointer, or simply great white, is a species of large Lamniformes, mackerel shark which can be found in the coastal surface waters of all the major ocea ...
's dorsal fin contains stabilizing
dermal The dermis or corium is a layer of skin between the epidermis (with which it makes up the cutis) and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from stress and strain. It is divided i ...
fibers that stiffen dynamically as it swims faster, helping it to control roll and yaw. File:Gymnarchus niloticus005 (long crop).JPG, The African knifefish propels itself with its full-length dorsal fin, keeping its back straight for electrolocation. File:Silurus costatus now in Platydoras sketch of Gronow 1754.jpg, Many
catfish Catfish (or catfishes; order (biology), order Siluriformes or Nematognathi) are a diverse group of ray-finned fish. Catfish are common name, named for their prominent barbel (anatomy), barbels, which resemble a cat's whiskers, though not ...
can lock their dorsal fin spines erect and secrete venom to discourage predators. File:White shark (cropped).jpg, The
great white shark The great white shark (''Carcharodon carcharias''), also known as the white shark, white pointer, or simply great white, is a species of large Lamniformes, mackerel shark which can be found in the coastal surface waters of all the major ocea ...
's dorsal fin contains stabilizing
dermal The dermis or corium is a layer of skin between the epidermis (with which it makes up the cutis) and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from stress and strain. It is divided i ...
fibers that stiffen dynamically as it swims faster to control roll and yaw. File:Istiophorus platypterus .jpg, Large retractable dorsal fin of the Indo-Pacific sailfish may serve to control the fish's temperature.
File:Orca wal 3.jpg, Male and female orcas have differently shaped dorsal fins. File:Ichthyosaurios5.jpg, Ichthyosaurs had diverse dorsal fin shapes.


Structure

A dorsal fin is a medial, unpaired fin that is located on the midline of the backs of some aquatic vertebrates. In development of the embryo in
teleost Teleostei (; Ancient Greek, Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts (), is, by far, the largest group of ray-finned fishes (class Actinopterygii), with 96% of all neontology, extant species of f ...
fish, the dorsal fin arises from sections of the skin that form a caudal fin fold. 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. These elements serve as attachment sites for epaxial muscles. 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. In these types of fish, the fins are made of two main components. The first component is the dermal fin rays known as lepidotrichia, and the
endoskeletal An endoskeleton (From Ancient Greek ἔνδον, éndon = "within", "inner" + σκελετός, skeletos = "skeleton") is a structural frame (skeleton) — usually composed of mineralized tissue — on the inside of an animal, overlaid by soft ...
base with associated muscles for movement is the second. File:Dorsal Fin Labeled Final.jpg, Dorsal fin of a perch showing the basals and radials of the pterygiophore that support the dorsal fin. File:Callionymus lyra dorsal fin male.jpg, Closeup of the dorsal fin of a common dragonet


See also

* Shark fin soup * Submarine sail *
Vertical stabilizer A vertical stabilizer or tail fin is the static part of the vertical tail of an aircraft. The term is commonly applied to the assembly of both this fixed surface and one or more movable rudders hinged to it. Their role is to provide control, sta ...


References

{{diversity of fish Vertebrate anatomy