Fish locomotion is the variety of types of animal locomotion used by
fish, principally by swimming. This however is achieved in different
groups of fish by a variety of mechanisms of propulsion in water, most
often by wavelike movements of the fish's body and tail, and in
various specialised fish by movements of the fins. The major forms of
locomotion in fish are anguilliform, in which a wave passes evenly
along a long slender body; sub-carangiform, in which the wave
increases quickly in amplitude towards the tail; carangiform, in which
the wave is concentrated near the tail, which oscillates rapidly;
thunniform, rapid swimming with a large powerful crescent-shaped tail;
and ostraciiform, with almost no oscillation except of the tail fin.
More specialised fish include movement by pectoral fins with a mainly
stiff body, as in the sunfish; and movement by propagating a wave
along the long fins with a motionless body in fish with electric
organs such as the knifefish.
In addition, some fish can variously "walk", i.e., move over land,
burrow in mud, and glide through the air.
1.1 Body/caudal fin propulsion
1.2 Median/paired fin propulsion
1.3 Dynamic lift
1.4.1 Body-caudal fin
Biplane body plan
Monoplane body plan
5 See also
7 Further reading
8 External links
Fish swim by exerting force against the surrounding water. There are
exceptions, but this is normally achieved by the fish contracting
muscles on either side of its body in order to generate waves of
flexion that travel the length of the body from nose to tail,
generally getting larger as they go along. The vector forces exerted
on the water by such motion cancel out laterally, but generate a net
force backwards which in turn pushes the fish forward through the
water. Most fishes generate thrust using lateral movements of their
body and caudal fin, but many other species move mainly using their
median and paired fins. The latter group swim slowly, but can turn
rapidly, as is needed when living in coral reefs for example. But they
can't swim as fast as fish using their bodies and caudal fins.
Body/caudal fin propulsion
There are five groups that differ in the fraction of their body that
is displaced laterally:
Eels propagate a more or less constant-sized flexion wave along their
In the anguilliform group, containing some long, slender fish such as
eels, there is little increase in the amplitude of the flexion wave as
it passes along the body.
The sub-carangiform group has a more marked increase in wave amplitude
along the body with the vast majority of the work being done by the
rear half of the fish. In general, the fish body is stiffer, making
for higher speed but reduced maneuverability.
The carangiform group, named for the Carangidae, are stiffer and
faster-moving than the previous groups. The vast majority of movement
is concentrated in the very rear of the body and tail. Carangiform
swimmers generally have rapidly oscillating tails.
Tunas such as the bluefin swim fast with their large crescent-shaped
The thunniform group contains high-speed long-distance swimmers, and
is characteristic of tunas and is also found in several lamnid
sharks. Here, virtually all the sideways movement is in the tail
and the region connecting the main body to the tail (the peduncle).
The tail itself tends to be large and crescent shaped.
The ostraciiform group have no appreciable body wave when they employ
caudal locomotion. Only the tail fin itself oscillates (often very
rapidly) to create thrust. This group includes Ostraciidae.
Median/paired fin propulsion
Boxfish use median-paired fin swimming, as they are not well
streamlined, and use primarily their pectoral fins to produce thrust.
Not all fish fit comfortably in the above groups. Ocean sunfish, for
example, have a completely different system, the tetraodontiform mode,
and many small fish use their pectoral fins for swimming as well as
for steering and dynamic lift.
Fish with electric organs, such as
those in the knifefish (Gymnotiformes), swim by undulating their very
long fins while keeping the body still, presumably so as not to
disturb the electric field that they generate.
Many fish swim using combined behavior of their two pectoral fins or
both their anal and dorsal fins. Different types of Median paired fin
propulsion can be achieved by preferentially using one fin pair over
the other, and include rajiform, diodontiform, amiiform, gymnotiform
and balistiform modes.
Rajiform locomotion is characteristic of rays, skates, and mantas when
thrust is produced by vertical undulations along large, well developed
Porcupine fish (here, Diodon nicthemerus) swim by undulating their
Diodontiform locomotion propels the fish propagating undulations along
large pectoral fins, as seen in the porcupinefish (Diodontidae).
Amiiform locomotion consists of undulations of a long dorsal fin while
the body axis is held straight and stable, as seen in the bowfin.
Gymnotus maintains a straight back while swimming to avoid disturbing
its electric sense.
Gymnotiform locomotion consists of undulations of a long anal fin,
essentially upside down amiiform, seen in the knifefish
In balistiform locomotion, both anal and dorsal fins undulate. It is
characteristic of the family Balistidae(triggerfishes). It may also be
seen in the Zeidae.
Oscillation is viewed as pectoral-fin-based swimming and is best known
as mobuliform locomotion. The motion can be described as the
production of less than half a wave on the fin, similar to a bird wing
flapping. Pelagic stingrays, such as the manta, cownose, eagle and bat
rays use oscillatory locomotion.
In tetraodontiform locomotion, the dorsal and anal fins are flapped as
a unit, either in phase or exactly opposing one another, as seen in
Tetraodontiformes (boxfishes and pufferfishes). The ocean sunfish
displays an extreme example of this mode.
In labriform locomotion, seen in the wrasses (Labriformes),
oscillatory movements of pectoral fins are either drag based or lift
based. Propulsion is generated either as a reaction to drag produced
by dragging the fins through the water in a rowing motion, or via lift
Sharks are denser than water, and must swim continually, using dynamic
lift from their pectoral fins.
Bone and muscle tissues of fish are denser than water. To maintain
depth fish such as sharks, but also some bony fish, increase buoyancy
by means of a gas bladder or by storing oils or lipids.
these features use dynamic lift instead. It is done using their
pectoral fins in a manner similar to the use of wings by airplanes and
birds. As these fish swim, their pectoral fins are positioned to
create lift which allows the fish to maintain a certain depth. The two
major drawbacks of this method are that these fish must stay moving to
stay afloat and that they are incapable of swimming backwards or
Similarly to the aerodynamics of flight, powered swimming requires
animals to overcome drag by producing thrust. Unlike flying, however,
swimming animals often do not need to supply much vertical force
because the effect of buoyancy can counter the downward pull of
gravity, allowing these animals to float without much effort. While
there is great diversity in fish locomotion, swimming behavior can be
classified into two distinct "modes" based on the body structures
involved in thrust production, Median-Paired
Fin (MPF) and Body-Caudal
Fin (BCF). Within each of these classifications, there are numerous
specifications along a spectrum of behaviours from purely undulatory
to entirely oscillatory. In undulatory swimming modes, thrust is
produced by wave-like movements of the propulsive structure (usually a
fin or the whole body). Oscillatory modes, on the other hand, are
characterized by thrust produced by swiveling of the propulsive
structure on an attachment point without any wave-like motion.
Sardines use body-caudal fin propulsion to swim, holding their
pectoral, dorsal, and anal fins flat against the body, creating a more
streamlined body to reduce drag.
Most fish swim by generating undulatory waves that propagate down the
body through the caudal fin. This form of undulatory locomotion is
Fin (BCF) swimming on the basis of the body
structures used; it includes anguilliform, sub-carangiform,
carangiform, and thunniform locomotory modes, as well as the
oscillatory ostraciiform mode.
Similar to adaptation in avian flight, swimming behaviors in fish can
be thought of as a balance of stability and maneuverability.
Because BCF swimming relies on more caudal body structures that can
direct powerful thrust only rearwards, this form of locomotion is
particularly effective for accelerating quickly and cruising
continuously. BCF swimming is, therefore, inherently stable and
is often seen in fish with large migration patterns that must maximize
efficiency over long periods. Propulsive forces in MPF swimming, on
the other hand, are generated by multiple fins located on either side
of the body that can be coordinated to execute elaborate turns. As a
result, MPF swimming is well adapted for high maneuverability and is
often seen in smaller fish that require elaborate escape patterns.
The habitats occupied by fishes are often related to their swimming
capabilities. On coral reefs, the faster-swimming fish species
typically live in wave-swept habitats subject to fast water flow
speeds, while the slower fishes live in sheltered habitats with low
levels of water movement.
Fish do not rely exclusively on one locomotor mode, but are rather
locomotor generalists, choosing among and combining behaviors from
many available behavioral techniques. At slower speeds, predominantly
BCF swimmers often incorporate movement of their pectoral, anal, and
dorsal fins as an additional stabilizing mechanism at slower
speeds, but hold them close to their body at high speeds to
improve streamlining and reducing drag.
Zebrafish have even been
observed to alter their locomotor behavior in response to changing
hydrodynamic influences throughout growth and maturation.
In addition to adapting locomotor behavior, controlling buoyancy
effects is critical for aquatic survival since aquatic ecosystems vary
greatly by depth.
Fish generally control their depth by regulating the
amount of gas in specialized organs that are much like balloons. By
changing the amount of gas in these swim bladders, fish actively
control their density. If they increase the amount of air in their
swim bladder, their overall density will become less than the
surrounding water, and increased upward buoyancy pressures will cause
the fish to rise until they reach a depth at which they are again at
equilibrium with the surrounding water.
See also: flying fish and flying and gliding animals
The transition of predominantly swimming locomotion directly to flight
has evolved in a single family of marine fish, the Exocoetidae. Flying
fish are not true fliers in the sense that they do not execute powered
flight. Instead, these species glide directly over the surface of the
ocean water without ever flapping their "wings."
Flying fish have
evolved abnormally large pectoral fins that act as airfoils and
provide lift when the fish launches itself out of the water.
Additional forward thrust and steering forces are created by dipping
the hypocaudal (i.e. bottom) lobe of their caudal fin into the water
and vibrating it very quickly, in contrast to diving birds in which
these forces are produced by the same locomotor module used for
propulsion. Of the 64 extant species of flying fish, only two distinct
body plans exist, each of which optimizes two different
Flying fish gain sufficient lift to glide above the water thanks to
their enlarged pectoral fins.
While most fish have caudal fins with evenly sized lobes (i.e.
homocaudal), flying fish have an enlarged ventral lobe (i.e.
hypocaudal) which facilitates dipping only a portion of the tail back
onto the water for additional thrust production and steering.
Because flying fish are primarily aquatic animals, their body density
must be close to that of water for buoyancy stability. This primary
requirement for swimming, however, means that flying fish are heavier
(have a larger mass) than other habitual fliers, resulting in higher
wing loading and lift to drag ratios for flying fish compared to a
comparably sized bird. Differences in wing area, wing span, wing
loading, and aspect ratio have been used to classify flying fish into
two distinct classifications based on these different aerodynamic
Biplane body plan
In the biplane or
Cypselurus body plan, both the pectoral and pelvic
fins are enlarged to provide lift during flight. These fish also
tend to have "flatter" bodies which increase the total lift producing
area thus allowing them to "hang" in the air better than more
streamlined shapes. As a result of this high lift production,
these fish are excellent gliders and are well adapted for maximizing
flight distance and duration.
Cypselurus flying fish have lower wing loading and
smaller aspect ratios (i.e. broader wings) than their Exocoetus
monoplane counterparts, which contributes to their ability to fly for
longer distances than fish with this alternative body plan. Flying
fish with the biplane design take advantage of their high lift
production abilities when launching from the water by utilizing a
"taxiing glide" in which the hypocaudal lobe remains in the water to
generate thrust even after the trunk clears the water's surface and
the wings are opened with a small angle of attack for lift
In the monoplane body plan of Exocoetus, only the pectoral fins are
abnormally large, while the pelvic fins are small.
Monoplane body plan
In the Exocoetus or monoplane body plan, only the pectoral fins are
enlarged to provide lift.
Fish with this body plan tend to have a more
streamlined body, higher aspect ratios (long, narrow wings), and
higher wing loading than fish with the biplane body plan, making these
fish well adapted for higher flying speeds.
Flying fish with a
monoplane body plan demonstrate different launching behaviors from
their biplane counterparts. Instead of extending their duration of
thrust production, monoplane fish launch from the water at high speeds
at a large angle of attack (sometimes up to 45 degrees). In this
way, monoplane fish are taking advantage of their adaptation for high
flight speed, while fish with biplane designs exploit their lift
production abilities during takeoff.
Main article: Walking fish
Alticus arnoldorum hopping
Alticus arnoldorum climbing up a vertical piece of Plexiglas
A "walking fish" is a fish that is able to travel over land for
extended periods of time. Some other cases of nonstandard fish
locomotion include fish "walking" along the sea floor, such as the
handfish or frogfish.
Most commonly, walking fish are amphibious fish. Able to spend longer
times out of water, these fish may use a number of means of
locomotion, including springing, snake-like lateral undulation, and
tripod-like walking. The mudskippers are probably the best
land-adapted of contemporary fish and are able to spend days moving
about out of water and can even climb mangroves, although to only
modest heights. The
Climbing gourami is often specifically
referred to as a "walking fish", although it does not actually "walk",
but rather moves in a jerky way by supporting itself on the extended
edges of its gill plates and pushing itself by its fins and tail. Some
reports indicate that it can also climb trees.
There are a number of fish that are less adept at actual walking, such
as the walking catfish. Despite being known for "walking on land",
this fish usually wriggles and may use its pectoral fins to aid in its
movement. Walking Catfish have a respiratory system that allows them
to live out of water for several days. Some are invasive species. A
notorious case in the
United States is the Northern snakehead.
Polypterids have rudimentary lungs and can also move about on land,
though rather clumsily. The
Mangrove rivulus can survive for months
out of water and can move to places like hollow logs.
There are some species of fish that can "walk" along the sea floor but
not on land; one such animal is the flying gurnard (it does not
actually fly, and should not be confused with flying fish). The
batfishes of the
Ogcocephalidae family (not to be confused with
Batfish of Ephippidae) are also capable of walking along the sea
floor. Bathypterois grallator, also known as a "tripodfish", stands on
its three fins on the bottom of the ocean and hunts for food. The
African lungfish (P. annectens) can use its fins to "walk" along the
bottom of its tank in a manner similar to the way amphibians and land
vertebrates use their limbs on land. 
Many fishes, particularly eel-shaped fishes such as true eels, moray
eels, and spiny eels, are capable of burrowing through sand or
mud. Ophichthids, the snake eels, are capable of burrowing either
forwards or backwards.
Role of skin in locomotion
Tradeoffs for locomotion in air and water
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depth look at fish swimming)
How fish swim: study solves muscle mystery
Simulated fish locomotion
Basic introduction to the basic principles of biologically inspired
The biomechanics of swimming
Diseases and parasites
Fish as food
Fear of fish
Hypoxia in fish
Sensory systems in fish
Ampullae of Lorenzini
Jamming avoidance response
Capacity for pain
Surface wave detection
Life history theory
Polyandry in fish
Fin and flipper locomotion
Tradeoffs for locomotion in air and water
Diel vertical migration
Sleep in fish
Fish common names
Fish on stamps
Glossary of ichthyology
Fins, limbs and wings
Fin and flipper locomotion
Flying and gliding animals
Evolution of fish
Evolution of tetrapods
Evolution of birds
Origin of birds
Origin of avian flight
Evolution of cetaceans
Tradeoffs for locomotion in air and water