Fish locomotion

Fish, like these yellowfin tuna, use many different mechanisms to propel themselves through water

Like a plane or submarine, a fish has six degrees of freedom

Eels propagate a more or less constant-sized flexion wave along their slender bodies.

Tunas such as the bluefin swim fast with their large crescent-shaped tails.

Boxfish use median-paired fin swimming, as they are not well streamlined, and use primarily their pectoral fins to produce thrust.

Porcupine fish (here, Diodon nicthemerus) swim by undulating their pectoral fins.

Gymnotus maintains a straight back while swimming to avoid disturbing its electric sense.

Sharks are denser than water and must swim continually to maintain depth, using dynamic lift from their pectoral fins.

Flying fish gain sufficient lift to glide above the water thanks to their enlarged pectoral fins.

In the monoplane body plan of Exocoetus, only the pectoral fins are abnormally large, while the pelvic fins are small.

Atlantic herring eggs, with a newly hatched larva

Freshly hatched herring larva in a drop of water compared to a match head.

In addition, some fish can variously "walk" (i.e., crawl over land using the pectoral and pelvic fins), burrow in mud, leap out of the water and even glide temporarily through the air.

- Fish locomotion

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Swim bladder

Internal gas-filled organ that contributes to the ability of many bony fish to control their buoyancy, and thus to stay at their current water depth without having to expend energy in swimming.

How gas is pumped into the swim bladder using counter-current exchange.

The West African lungfish possesses a lung homologous to swim bladders

Most mesopelagic fishes are small filter feeders which ascend at night using their swimbladders to feed in the nutrient rich waters of the epipelagic zone. During the day, they return to the dark, cold, oxygen deficient waters of the mesopelagic where they are relatively safe from predators. Lanternfish account for as much as 65 percent of all deep sea fish biomass and are largely responsible for the deep scattering layer of the world's oceans.

Swim bladder display in a Malacca shopping mall

Swim bladder disease has resulted in this female ryukin goldfish floating upside down

Some of them can control their depth only by swimming (using dynamic lift); others store fats or oils with density less than that of seawater to produce a neutral or near neutral buoyancy, which does not change with depth.

Skate (fish)

Skates are cartilaginous fish belonging to the family Rajidae in the superorder Batoidea of rays.

Early Eocene fossil stingray Heliobatis radians

A skate is caught in the Outer Banks using a Carolina rig

Full view of a skate's mermaid's purse. Roughly 125 mm in length.

The fibers of the skate electric organ are embedded in the muscles located lateral to the notochord in the tail.

Four developing embryos located in an opened big skate egg case (mermaid's purse)

The flattened body shape, ventral eyes and well developed spiracles of the skate allows them to live benthically, buried in the sediment or using a longitudinal undulation of the pectoral fins known as Rajiform locomotion to glide along the water floor.

Fish fin

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

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

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

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

An example is the Robot Tuna built by the Institute of Field Robotics, to analyze and mathematically model thunniform motion.

Tetraodontiformes

Order of highly derived ray-finned fish, also called the Plectognathi.

Long-spine porcupinefish, Diodon holocanthus: On the right is a blue-spotted grouper, Cephalopholis argus

The honeycomb cowfish is part of the family Ostraciidae.

American whitespotted filefish Cantherhines macrocerus

Most members of this order – except for the family Balistidae – are ostraciiform swimmers, meaning the body is rigid and incapable of lateral flexure.

Fish anatomy

Study of the form or morphology of fish.

Skeletal structure of a bass showing the vertebral column running from the head to the tail

Skull bones as they appear in a seahorse

Positions of fish mouths: terminal (a), superior (b), and subterminal or inferior (c).

Illustration of barbels on the head of a fish

Moray eels have two sets of jaws: the oral jaws that capture prey and the pharyngeal jaws that advance into the mouth and move prey from the oral jaws to the esophagus for swallowing.

Placoid scales from a shark. A: Epidermis; B: Dermis; C: Pulp core; D: Dentine; E: Basal plate; F: Enamel; G: Spine

Fish scales. 1: Cycloid scale; 2: Ctenoid scale; 3: Placcoid scale; 4: Ganoid scale

Fish scales. A: Ganoid; B: Cycloid; C: Ctenoid

The lateral line is clearly visible as a line of receptors running along the side of this Atlantic cod.

Sharks possess a heterocercal caudal fin. The dorsal portion is usually larger than the ventral portion.

The high performance bigeye tuna is equipped with a homocercal caudal fin, finlets and keels.

Internal organs of a male yellow perch: A=gill, B=Heart atrium, C=Heart ventricle, D=Liver (cut), E=Stomach, F=Pyloric caeca, G=Swim bladder, H=Intestine, I=Testis, J=Urinary bladder

The black swallower is a species of deep sea fish with an extensible stomach which allows it to swallow fish larger than itself.

Internal organs of a female Atlantic cod: 1=Liver, 2=Gas bladder, 3=Ovary, 4=Pyloric caeca, 5=Stomach, 6=Intestine

Dorsal view of the brain of the rainbow trout

Cross-section of the brain of a porbeagle shark with the cerebellum highlighted

Skull of Tiktaalik, a genus of extinct sarcopterygian (lobe-finned "fish") from the late Devonian period

Pectoral fins: Found in pairs on each side, usually just behind the operculum. Pectoral fins are homologous to the forelimbs of tetrapods, and aid walking in several fish species such as some anglerfish and the mudskipper. A peculiar function of pectoral fins, highly developed in some fish, is the creation of the dynamic lifting force that assists some fish such as sharks in maintaining depth and also enables the "flight" for flying fish. Certain rays of the pectoral fins may be adapted into finger-like projections, such as in sea robins and flying gurnards.

Aquatic locomotion

Biologically propelled motion through a liquid medium.

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)

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

Nile crocodile (Crocodylus niloticus) swimming

Immature Hawaiian green sea turtle in shallow waters

Comparative skeletal anatomy of a typical otariid seal and a typical phocid seal

From the point of view of aquatic propulsion, the descent of modern members of the class Reptilia from archaic tailed Amphibia is most obvious in the case of the order Crocodilia (crocodiles and alligators), which use their deep, laterally compressed tails in an essentially carangiform mode of propulsion (see Fish locomotion).