A report on Fin and Aquatic locomotion

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Jellyfish in motion
Fins are used by aquatic animals, such as this orca, to generate thrust and control the subsequent motion
A eurasian coot swimming
Caudal fin of a great white shark
The flagellum of a Gram-negative bacteria is rotated by a molecular motor at its base
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
Salmon spermatozoa for artificial propagation
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.
Shrimp paddle with special swimming legs (pleopods)
In a parallel but independent evolution, the ancient reptile Ichthyosaurus communis developed fins (or flippers) very similar to fish (or dolphins)
Daphnia swims by beating its antennae
In the 1990s the CIA built a robotic catfish called Charlie to test the feasibility of unmanned underwater vehicles
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

The use of fins for the propulsion of aquatic animals can be remarkably effective.

- Fin

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

- Aquatic locomotion
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1 related topic with Alpha

Overall

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

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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
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.

Their principal function is to help the fish swim.