Fin

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Fins are used by aquatic animals, such as this orca, to generate thrust and control the subsequent motion
Caudal fin of a great white shark
Aquatic animals typically use fins for locomotion
(1) pectoral fins (paired), (2) pelvic fins (paired), (3) dorsal fin, (4) adipose fin, (5) anal fin, (6) caudal (tail) fin
Comparison between A) the swimming fin of a lobe-finned fish and B) the walking leg of a tetrapod. Bones considered to correspond with each other have the same color.
In a parallel but independent evolution, the ancient reptile Ichthyosaurus communis developed fins (or flippers) very similar to fish (or dolphins)
In the 1990s the CIA built a robotic catfish called Charlie to test the feasibility of unmanned underwater vehicles

Thin component or appendage attached to a larger body or structure.

- Fin
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Ray fins on a teleost fish, Hector's lanternfish 
(1) pectoral fins (paired), (2) pelvic fins (paired), (3) dorsal fin,
(4) adipose fin, (5) anal fin, (6) caudal (tail) fin

Fish fin

Ray fins on a teleost fish, Hector's lanternfish 
(1) pectoral fins (paired), (2) pelvic fins (paired), (3) dorsal fin,
(4) adipose fin, (5) anal fin, (6) caudal (tail) fin
Skeleton of a ray-finned fish
Lobe-finned fishes, like this coelacanth, have fins that are borne on a fleshy, lobelike, scaly stalk extending from the body. Due to the high number of fins it possesses, the coelacanth has high maneuverability and can orient their bodies in almost any direction in the water.
The haddock, a type of cod, is ray-finned. It has three dorsal and two anal fins
Cartilaginous fishes, like this shark, have fins that are elongated and supported with soft and unsegmented rays named ceratotrichia, filaments of elastic protein resembling the horny keratin in hair and feathers
Caudal fin of a grey reef shark
Shark fin
Comparison between A) the swimming fin of a lobe-finned fish and B) the walking leg of a tetrapod. Bones considered to correspond with each other have the same color.
In a parallel but independent evolution, the ancient reptile Ichthyosaurus communis developed fins (or flippers) very similar to fish (or dolphins)
Similar adaptations for fully aquatic lifestyle are found both in dolphins and ichthyosaurs
In the 1990s, the CIA built a robotic catfish called Charlie, designed to collect underwater intelligence undetected

Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish.

Cetacea

Infraorder of aquatic mammals that includes whales, dolphins, and porpoises.

Infraorder of aquatic mammals that includes whales, dolphins, and porpoises.

Dolphin anatomy
Humpback whale fluke
Biosonar
Bubble net feeding
Killer whale porpoising
Two views of the skeletons of Dorudon atrox, extinct for 40 million years, and Maiacetus inuus, extinct for 47.5 million years, in the swimming position for comparison.
Cetaceans display convergent evolution with fish and aquatic reptiles
Fossil of a Maiacetus (red, beige skull) with fetus (blue, red teeth) shortly before the end of gestation
Whales caught 2010–2014, by country
Dominoes made of baleen
A whale as depicted by Conrad Gesner, 1587, in Historiae animalium
"Destruction of Leviathan" engraving by Gustave Doré, 1865
Silver coin with Tarus riding a dolphin
Constellation Cetus
Depiction of baleen whaling, 1840
Stranded sperm whale engraving, 1598
Sea World show featuring bottlenose dolphins and false killer whales
Ulises the orca, 2009
Dawn Brancheau doing a show four years before the incident
SeaWorld pilot whale with trainers

The fluke is set horizontally on the body, unlike fish, which have vertical tails.

Dorsal fin of a shark

Dorsal fin

Dorsal fin of a shark
Most fish, like this Prussian carp, have one dorsal fin
Sharks typically have two dorsal fins
The yellowfin tuna also has two dorsal fins
Haddocks have three dorsal fins
Differences of dorsal fins of orcas between male and female
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.<ref>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{{dead link|date=September 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>
Large retractable dorsal fin of the Indo-Pacific sailfish
Various species of Ichthyosaurs displaying different types of dorsal fins
Dorsal fin of a perch showing the basals and radials of the pterygiophore that support the dorsal fin.
Closeup of the dorsal fin of a common dragonet

A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom.

Pelvic fins from a Java barb (Barbonymus gonionotus)

Pelvic fin

Pelvic fins from a Java barb (Barbonymus gonionotus)
The pelvic fin appears at roughly 21 days post fertilization in zebrafish
Pelvic fin skeleton for Danio rerio, zebrafish.
Gobiids have modified their pelvic fins into adhesive suckers.
Lumpsuckers use their modified pelvic fins to adhere to the substrate.

Pelvic fins or ventral fins are paired fins located on the ventral surface of fish.

Traditional target arrow (top) and replica medieval arrow (bottom).

Arrow

Traditional target arrow (top) and replica medieval arrow (bottom).
Modern arrow with plastic fletchings and nock.
Warring States bronze arrowheads
Schematic of an arrow with many parts.
A sideprofile of an Easton Carbon One arrow with a spine of 900, taken with a scanning electron microscope (SEM). The arrow is a bond of two carbon tubes, an inner and an outer tube (black wires). In between both carbon layers, another fiber is used (white fiber). This second fiber is an Mg-Al-Si-fiber. The "white" fiber is twisted around the inner carbon tube. The fibers of the carbon tubes are not twisted, to ensure a maximum of possible mechanical tension of the arrow. The Mg-Al-Si-fiber enhances the flexibility of the arrow. The diameter of a single carbon fiber is approx. 7 µm.
Obsidian broadhead
Ancient Greek bronze arrowhead, 4th century BC, from Olynthus, Chalcidice
Various Japanese arrowheads
Native American arrowheads
20th century field points
Modern replicas of various medieval European arrowheads
Straight parabolic fletchings on an arrow.

An arrow is a fin-stabilized projectile launched by a bow.

Pinniped

Restoration of Puijila
Fossil of Enaliarctos
Fossil skull cast of Piscophoca sp. from Phocidae
Reconstruction of Archaeodobenus akamatsui family Odobenidae
Male and female South American sea lions, showing sexual dimorphism
Light reflection on an elephant seal eye
Frontal view of brown fur seal head
Vibrissae of walrus
Weddell seal underwater
Northern elephant seal resting in water
Walrus on ice off Alaska. This species has a discontinuous distribution around the Arctic Circle.
Harbor seal hauled out on rock
Steller sea lion with white sturgeon
Leopard seal capturing emperor penguin
Orca hunting a Weddell seal
Walrus herd on ice floe
Northern fur seal breeding colony
Male northern elephant seals fighting for dominance and females
Harp seal mother nursing pup
Adult Antarctic fur seal with pups
Walrus males are known to use vocalizations to attract mates.
Sea lion balancing a ball
Inuit seal sculptures at the Linden Museum
Captive sea lion at Kobe Oji Zoo Kobe, Japan
Men killing northern fur seals on Saint Paul Island, Alaska, in the mid-1890s
Protests of Canada's seal hunts
Grey seal on beach occupied by humans near Niechorze, Poland. Pinnipeds and humans may compete for space and resources.

Pinnipeds (pronounced ), commonly known as seals, are a widely distributed and diverse clade of carnivorous, fin-footed, semiaquatic, mostly marine mammals in the clade Pinnipedia.

Feather fletching – these are shield cut with barred red hen feathers and a solid white cock.

Fletching

Feather fletching – these are shield cut with barred red hen feathers and a solid white cock.
Plastic fletching (also known as vanes) – this example is parabolic cut with pink hen vanes (the ones put oblique to the bow when nocked on the string) and a green cock (the one – or ones, with even-numbered vanes – put perpendicular to it).

Fletching is the fin-shaped aerodynamic stabilization device attached on arrows, bolts, darts, or javelins, and are typically made from light semi-flexible materials such as feathers or bark.

Fish

Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits.

Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits.

Dunkleosteus was a gigantic, 10 m long prehistoric fish of class Placodermi.
Lower jaw of the placoderm Eastmanosteus pustulosus, showing the shearing structures ("teeth") on its oral surface; from the Devonian of Wisconsin
Leedsichthys, of the subclass Actinopterygii, is the largest known fish, with estimates in 2005 putting its maximum size at 16 m.
A relative of the seahorses, the leafy seadragon's appendages allow it to camouflage (in the form of crypsis) with the surrounding seaweed.
The psychedelic mandarin dragonet is one of only two animal species known to have blue colouring because of cellular pigment.
Diversity of various groups of fish (and other vertebrates) through time
Lungfish are the closest living relatives of tetrapods (four-limbed vertebrates).
The bowfin Amia calva is the sole survivor of the halecomorph clade.
Organs: 1. Liver, 2. Gas bladder, 3. Roe, 4. Pyloric caeca, 5. Stomach, 6. Intestine
Tuna gills inside the head. The fish head is oriented snout-downwards, with the view looking towards the mouth.
Didactic model of a fish heart
Dorsal view of the brain of the rainbow trout
The anatomy of Lampanyctodes hectoris (1) operculum (gill cover), (2) lateral line, (3) dorsal fin, (4) fat fin, (5) caudal peduncle, (6) caudal fin, (7) anal fin, (8) photophores, (9) pelvic fins (paired), (10) pectoral fins (paired)
Swim bladder of a rudd (Scardinius erythrophthalmus)
Ovary of fish (Corumbatá)
French grunts – Haemulon flavolineatum
Whale sharks, the largest species of fish, are classified as vulnerable.
These fish-farming ponds were created as a cooperative project in a rural village.
Fish counter display at the Oulu Market Hall in Oulu, Finland.
A Bengali fish vendor
Avatar of Vishnu as a Matsya
The ichthus is a Christian symbol of a fish signifying that the person who uses it is a Christian.
These goldband fusiliers are schooling because their swimming is synchronised.
Agnatha (Pacific hagfish)
Chondrichthyes (Horn shark)
Actinopterygii (Brown trout)
Sarcopterygii (Coelacanth)
Egg of lamprey
Egg of catshark (mermaids' purse)
Egg of bullhead shark
Egg of chimaera

In biology, the term fish is most strictly used to describe any animal with a backbone, gills throughout life, and limbs (if any) in the shape of fins. Many types of aquatic animals with common names ending in "fish" are not fish in this sense; examples include shellfish, cuttlefish, starfish, crayfish and jellyfish. In earlier times, even biologists did not make a distinction – sixteenth century natural historians classified also seals, whales, amphibians, crocodiles, even hippopotamuses, as well as a host of aquatic invertebrates, as fish.

Jellyfish in motion

Aquatic locomotion

Biologically propelled motion through a liquid medium.

Biologically propelled motion through a liquid medium.

Jellyfish in motion
A eurasian coot swimming
The flagellum of a Gram-negative bacteria is rotated by a molecular motor at its base
Salmon spermatozoa for artificial propagation
Shrimp paddle with special swimming legs (pleopods)
Daphnia swims by beating its antennae
Octopuses swim headfirst, with arms trailing behind
Jellyfish pulsate their bell for a type of jet locomotion
Scallops swim by clapping their two shells open and closed
Open water fish, like this Atlantic bluefin tuna, are usually streamlined for straightline speed, with a deeply forked tail and a smooth body shaped like a spindle tapered at both ends.
Many reef fish, like this queen angelfish, have a body flattened like a pancake, with pectoral and pelvic fins that act with the flattened body to maximize manoeuvrability.
The leopard shark angles its pectoral fins so they behave as hydrofoils to control the animal's pitch
The slowest-moving fishes are the sea horses, often found in reefs
Common toad (Bufo bufo) swimming
Nile crocodile (Crocodylus niloticus) swimming
Immature Hawaiian green sea turtle in shallow waters
Macroplata
Comparative skeletal anatomy of a typical otariid seal and a typical phocid seal
Animated representation of lobstering
Chinstrap penguin leaping over water
Swimming dog

Hydrofoils, or fins, are used to push against the water to create a normal force to provide thrust, propelling the animal through water.

The Soyuz TMA-9 spacecraft launches from the Baikonur Cosmodrome, Site 1/5 in Kazakhstan

Rocket

Spacecraft, aircraft, vehicle or projectile that obtains thrust from a rocket engine.

Spacecraft, aircraft, vehicle or projectile that obtains thrust from a rocket engine.

The Soyuz TMA-9 spacecraft launches from the Baikonur Cosmodrome, Site 1/5 in Kazakhstan
Depiction of rocket arrows, from the Huolongjing. The left arrow reads 'fire arrow' (huo jian), the middle is an 'dragon shaped arrow frame' (long xing jian jia), and the left is a 'complete fire arrow' (huo jian quan shi)
An East India Company battalion was defeated during the Battle of Guntur, by the forces of Hyder Ali, who effectively utilized Mysorean rockets and rocket artillery.
William Congreve at the bombardment of Copenhagen (1807) during the Napoleonic Wars.
Goddard with a liquid oxygen-gasoline rocket (1926)
A V-2 rocket launched from Test Stand VII in summer 1943
Viking 5C rocket engine
Gas Core light bulb
Illustration of the pendulum rocket fallacy. Whether the motor is mounted at the bottom (left) or top (right) of the vehicle, the thrust vector (T) points along an axis that is fixed to the vehicle (top), rather than pointing vertically (bottom) independent of vehicle attitude, which would lead the vehicle to rotate.
A Trident II missile launched from sea.
A Bumper sounding rocket
Apollo LES pad abort test with boilerplate crew module.
Doglegged flight path of a PSLV launch to polar inclinations avoiding landmass.
Workers and media witness the Sound Suppression Water System test at Launch Pad 39A.
A balloon with a tapering nozzle. In this case, the nozzle itself does not push the balloon but is pulled by it. A convergent/divergent nozzle would be better.
Rocket thrust is caused by pressures acting on both the combustion chamber and nozzle
Forces on a rocket in flight
A map of approximate Delta-v's around the Solar System between Earth and Mars
The Tsiolkovsky rocket equation gives a relationship between the mass ratio and the final velocity in multiples of the exhaust speed
Spacecraft staging involves dropping off unnecessary parts of the rocket to reduce mass.
Apollo 6 while dropping the interstage ring
during launch phase
torn apart T+73 seconds after hot gases escaped the SRBs, causing the breakup of the Shuttle stack
A battery of Soviet Katyusha rocket launchers fires at German forces during the Battle of Stalingrad, 6 October 1942

They may also have one or more rocket engines, directional stabilization device(s) (such as fins, vernier engines or engine gimbals for thrust vectoring, gyroscopes) and a structure (typically monocoque) to hold these components together.