Dorsal fin

Dorsal fin of a shark

A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fish, cetaceans (whales, dolphins, and porpoises), and the (extinct) ichthyosaurs. Depending on the species, an animal may have one or two of them.

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

The bony or cartilaginous bones that support the base of the dorsal fin in fish are called pterygiophores.

Functions

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.

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.^[1] 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 also after periods of high activity, presumably to cool down.^[1][2]

• 

  Dorsal fin of an orca

• 

  The dorsal fin of a white shark contains dermal fibers that work "like riggings that stabilize a ship's mast", and stiffen dynamically as the shark swims faster to control roll and yaw.^[1]

• 

  Large retractable dorsal fin of the Indo-Pacific sailfish

• 

  Closeup of the dorsal fin of a common dragonet

1. ^ Lingham‐Soliar T (2005) "Dorsal fin in the white shark, Carcharodon carcharias: A dynamic stabilizer for fast swimming" Journal of Morphology, 263 (1): 1–11. doi:10.1002/jmor.10207 pdf

See also

Look up dorsal in Wiktionary, the free dictionary.

• Fish fin
• Submarine sail
• Vertical stabilizer

Notes

Fins, limbs and wings
Fins	Aquatic locomotion Cephalopod fin Fish locomotion Fin and flipper locomotion Caudal fin Dorsal fin Fish fin flipper Lobe-finned fish Ray-finned fish Pectoral fins
Limbs	Limb development Limb morphology digitigrade plantigrade unguligrade uniped biped facultative biped triped quadruped Arthropod Cephalopod Tetrapod dactyly Digit
Wings	Flying and gliding animals Bat wing Bird wing keel skeleton feathers Insect wing Pterosaur wing Wingspan
Evolution	Evolution of fish Evolution of tetrapods Evolution of birds Origin of birds Origin of avian flight Evolution of cetaceans Comparative anatomy Convergent evolution Analogous structures Homologous structures
Related	Animal locomotion Gait Robot locomotion Samara Terrestrial locomotion Tradeoffs for locomotion in air and water Rotating locomotion Undulatory locomotion

Fish
About fish	Diversity Ethnoichthyology Evolution Diseases and parasites Fisheries Fishing Fish as food Fear of fish FishBase Fish kill Hypoxia in fish Ichthyology
Anatomy and physiology	Fish anatomy Fish physiology Estimating age Anguilliformity Bone dermal intramembranous ossification Cleithrum Chromatophore Fins dorsal fin Gill branchial arch gill raker gill slit pharyngeal arch pharyngeal slit pseudobranch Glossohyal Jaw hyomandibula pharyngeal jaw Leydig's organ Mauthner cell Meristics Operculum papillare Papilla Photophore Root effect Shark cartilage Scales ganoine Spiral valve Suckermouth Swim bladder physoclisti physostome Teeth pharyngeal teeth shark teeth Teleost leptins Digital Library
Sensory systems	Sensory systems in fish Ampullae of Lorenzini Barbel Hydrodynamic reception Electrocommunication Electroreception Jamming avoidance response Lateral line Otolith Passive electrolocation Capacity for pain Schreckstoff Surface wave detection Vision Weberian apparatus
Reproduction	Fish reproduction Bubble nest Clasper Egg case Fish development Ichthyoplankton Juvenile fish Life history theory Milt Mouthbrooder Polyandry in fish Pregnancy Roe Sequential hermaphroditism Spawning triggers
Locomotion	Fish locomotion Fin and flipper locomotion Amphibious fish Walking fish Flying fish Undulatory locomotion Tradeoffs for locomotion in air and water RoboTuna
Other behaviour	Aquatic predation Aquatic respiration Bait ball Bottom feeders Cleaner fish Diel vertical migration Electric fish Filter feeders Forage fish Migrating fish Paedophagy Predatory fish Salmon run Sardine run Scale eaters Schooling fish Sleep in fish Venomous fish Fish intelligence
By habitat	Cave Coastal Coldwater Coral reef Deep sea Demersal Euryhaline Freshwater Groundfish Pelagic Tropical
Other types	Bait Coarse Diversity Game Genetically modified Hallucinogenic Oily Poisonous Rough Whitefish
Commercial	Fish farming Carp Salmonids Tilapia Wild fisheries Predatory fish billfish mackerel salmon tuna Forage fish anchovy herring sardine sprats Demersal fish cod flatfish pollock
Major groups	Jawless fish hagfish lampreys Cartilaginous fish chimaeras sharks rays Bony fish spiny-finned fleshy-finned
Lists	Aquarium life Blind fish Fish common names Fish families Fish on stamps Glossary of ichthyology Large fish Threatened rays sharks Prehistoric fish more lists...
Category Portal WikiProject