Editing Fish locomotion (section)

==Swimming==

=== Mechanism ===

{{Further|Fish fin}}
[[File:Lampanyctodes hectoris (fins).png|thumb|right|upright=1.2|Fins used for locomotion: (1) pectoral fins (paired), (2) [[pelvic fin]]s (paired), (3) [[dorsal fin]], (4) adipose fin, (5) anal fin, (6) [[caudal fin|caudal (tail) fin]] ]]

Fish swim by exerting force against the surrounding water. There are exceptions, but this is normally achieved by the fish contracting [[muscle]]s 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 [[Euclidean vector|vector]] [[force]]s 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 not swim as fast as fish using their bodies and caudal fins.<ref name=Breder/><ref name=Sfakiotakis/>

[[File:Skeletal anatomy of tilapia.png|thumb|left|upright=1.5|Skeletal anatomy of ''[[Tilapia]]''<ref name=GeSCI2021>[https://oer-studentresources.gesci.org/wp-content/courses/Biology/Bio-F4-Support-and-Movement-Plants-and-Animals/locomotion_in_finned_fish.html Locomotion in Finned Fish], ''[[Global e-Schools and Communities Initiative]]'' (GeSCI) United Nations. Retrieved 7 Sep 2021. [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>]]

Consider the [[tilapia]] shown in the diagram. Like most fish, the tilapia has a streamlined body shape reducing water resistance to movement and enabling the tilapia to cut easily through water. Its head is inflexible, which helps it maintain forward thrust.<ref name=GeSCI2021 /> Its [[Fish scale|scales]] overlap and point backwards, allowing water to pass over the fish without unnecessary obstruction. Water friction is further reduced by mucus which tilapia secrete over their body.<ref name=GeSCI2021 />

[[File:6DOF en.jpg|thumb|right|Like a plane or submarine, a fish has [[six degrees of freedom]].]]

The backbone is flexible, allowing muscles to contract and relax rhythmically and bring about undulating movement.<ref name=GeSCI2021 /> A [[swim bladder]] provides buoyancy which helps the fish adjust its vertical position in the [[water column]]. A [[lateral line]] system allows it to detect vibrations and pressure changes in water, helping the fish to respond appropriately to external events.<ref name=GeSCI2021 />

Well developed fins are used for maintaining balance, braking and changing direction. The pectoral fins act as pivots around which the fish can turn rapidly and steer itself. The paired pectoral and pelvic fins control [[Pitch (aviation)|pitching]], while the unpaired dorsal and anal fins reduce [[Yaw (rotation)|yawing]] and [[Roll (flight)|rolling]]. The caudal fin provides raw power for propelling the fish forward.<ref name=GeSCI2021 />

=== Body/caudal fin propulsion ===
There are five groups that differ in the fraction of their body that is displaced laterally:<ref name=Breder>{{cite journal | last1 = Breder | first1 = CM | year = 1926 | title = The locomotion of fishes | journal = Zoologica | volume = 4 | pages = 159–297 }}</ref>

==== Anguilliform<!--This term redirects here!--> ====
{{Redirect2|Anguilliform|Anguilliforms|Anguilliformes, the order of ray-finned fishes|Eel}}
[[File:FMIB 35739 Anguilla vulgaris -- Anguilla.jpeg|thumb|[[Eel]]s propagate a more or less constant-sized flexion wave along their slender bodies.]]

In the anguilliform group, containing some long, slender fish such as [[eel]]s, there is little increase in the amplitude of the flexion wave as it passes along the body.<ref name=Breder/><ref>Long Jr, J. H., Shepherd, W., & Root, R. G. (1997). [https://web.archive.org/web/20160122095453/http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA330550#page=122 Manueuverability and reversible propulsion: How eel-like fish swim forward and backward using travelling body waves".] In: ''Proc. Special Session on Bio-Engineering Research Related to Autonomous Underwater Vehicles'', 10th Int. Symp. Unmanned Untethered Submersible Technology (pp. 118–134).</ref>

==== Subcarangiform ====
{{Anchor|Sub-carangiform}} <!--alt spelling-->
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The subcarangiform 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. [[Trout]] use sub-carangiform locomotion.<ref name=Breder/>

==== Carangiform ====
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{{Redirect2|Carangiform|Carangiforms|the order of ray-finned fishes|Carangiformes}}

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.<ref name=Breder/>

==== Thunniform ====
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[[File:Bluefin-big.jpg|thumb|Tunas such as the [[bluefin tuna (disambiguation)|bluefin]] swim fast with their large crescent-shaped tails.]]

The thunniform group contains high-speed long-distance swimmers, and is characteristic of [[tuna]]s<ref name=Hawkins>{{cite journal | last1 = Hawkins | first1 = JD | last2 = Sepulveda | first2 = CA | last3 = Graham | first3 = JB | last4 = Dickson | first4 = KA | year = 2003 | title = Swimming performance studies on the eastern Pacific bonito ''Sarda chiliensis'', a close relative of the tunas (family Scombridae) II. Kinematics | journal = The Journal of Experimental Biology | volume = 206 | issue = 16| pages = 2749–2758 | doi = 10.1242/jeb.00496 | pmid = 12847120 | doi-access = free }}</ref> and is also found in several [[Lamnidae|lamnid sharks]].<ref>{{cite book | first = A. Peter | last = Klimley | title = The Biology of Sharks, Skates, and Rays | publisher = University of Chicago Press | date = 2013 | isbn = 978-0-226-44249-5}}</ref> 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.<ref name=Breder/>

====Ostraciiform ====
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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]].<ref name=Breder/>

=== Median/paired fin propulsion ===
[[File:Lactoria cornuta aka longhorn cowfish in cph aquarium 2007.jpg|thumb|alt=A bright yellow boxfish swims with its pectoral fins only.|[[Ostraciidae|Boxfish]] use median-paired fin swimming, as they are not well streamlined, and use primarily their [[pectoral fin]]s to produce thrust.]]{{See also|Batoid locomotion}}
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 fin]]s for swimming as well as for steering and [[#Dynamic lift|dynamic lift]]. Fish in the order [[Gymnotiformes]] possess electric organs along the length of their bodies and swim by undulating an elongated anal fin 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 [[fish anatomy#Fins|pectoral fins]] or both their [[fish anatomy#Fins|anal]] and [[fish anatomy#Fins|dorsal]] fins. Different types of [[Aquatic locomotion#Median paired fin (MPF) propulsion|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.<ref name=Sfakiotakis/>

====Rajiform====

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Rajiform locomotion is characteristic of [[Batoidea|rays]] and [[Skates (fish)|skate]]s, when thrust is produced by vertical undulations along large, well developed pectoral fins.<ref name=Sfakiotakis/>

====Diodontiform====

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[[File:Pindsvinefisk Diodon holocanthus.jpg|thumb|Porcupine fish (here, ''[[Diodon holocanthus]]'') swim by undulating their pectoral fins.]]

Diodontiform locomotion propels the fish propagating undulations along large pectoral fins, as seen in the porcupinefish ([[Diodontidae]]).<ref name=Sfakiotakis/>

====Amiiform====
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{{Redirect2|Amiiform|Amiiforms|the order of bowfin fishes|Amiiformes}}

Amiiform locomotion consists of undulations of a long dorsal fin while the body axis is held straight and stable, as seen in the [[bowfin]].<ref name=Sfakiotakis/>

====Gymnotiform====
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{{Redirect2|Gymnotiform|Gymnotiforms|the order of teleost bony fishes commonly known as the Neotropical or South American knifefish|Gymnotiformes}}

[[File:Gymnotus_sp.jpg|thumb|upright=1.6<!--keep image area approx. equal-->|''[[Gymnotus]]'' maintains a straight back while swimming to avoid disturbing [[Electroreception and electrogenesis|its electric sense]].]]

Gymnotiform locomotion consists of undulations of a long anal fin, essentially upside down amiiform, seen in the South American knifefish ''[[Gymnotiformes]]''.<ref name=Sfakiotakis/>

====Balistiform====

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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]].<ref name=Sfakiotakis/>

====Oscillatory====
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.<ref name="Lindsey">{{cite book|author=Lindsey, C.C.|year=1978|pages=1–100|title=Fish Physiology|volume=7|chapter=Locomotion|editor=Hoar W.S. |editor2=Randall, D.J.|publisher=Academic Press. San Francisco}}</ref>

=====Tetraodontiform=====

In tetraodontiform locomotion, the dorsal and anal fins are flapped as a unit, either in phase or exactly opposing one another, as seen in the [[Tetraodontiformes]] ([[boxfish]]es and [[pufferfish]]es). The [[ocean sunfish]] displays an extreme example of this mode.<ref name=Sfakiotakis/>

=====Labriform=====

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 mechanisms.<ref name=Sfakiotakis/><ref>{{cite journal | last1 = Fulton | first1 = CJ | last2 = Johansen | first2 = JL | last3 = Steffensen | first3 = JF | year = 2013 | title = Energetic extremes in aquatic locomotion by coral reef fishes | journal = PLOS ONE | volume = 8 | issue = 1| page = e54033 | doi=10.1371/journal.pone.0054033| pmid = 23326566 | pmc = 3541231 | bibcode = 2013PLoSO...854033F | doi-access = free }}</ref>

{{anchor|Shark locomotion}}

===Dynamic lift===
[[File:Tiburón.jpg|thumb|[[Shark]]s are denser than water and must swim continually to maintain depth, using [[dynamic lift]] from their pectoral fins.]]

Bone and muscle tissues of fish are denser than water. To maintain depth, bony fish increase [[buoyancy]] by means of a [[gas bladder]]. Alternatively, [[oily fish|some fish]] store oils or [[lipids]] for this same purpose. Fish without these features use [[dynamic lift]] instead. It is done using their pectoral fins in a manner similar to the use of wings by [[airplane]]s and [[bird]]s. As these fish swim, their pectoral fins are positioned to create [[lift (force)|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 hovering.<ref>{{cite web | url=http://www.textbookleague.org/73shark.htm | title=Deep Breathing | author=Bennetta, William J. | year=1996 | access-date=2007-08-28 | archive-url=https://web.archive.org/web/20070814075030/http://www.textbookleague.org/73shark.htm | archive-date=2007-08-14 | url-status=usurped }}</ref><ref>{{cite web | url=http://www.flmnh.ufl.edu/fish/education/questions/basics.html#sleep | title=Do sharks sleep | publisher=Flmnh.ufl.edu | archive-url=https://web.archive.org/web/20100918164840/http://www.flmnh.ufl.edu/fish/education/questions/basics.html#sleep | archive-date=2010-09-18| date=2017-05-02 }}</ref>

===Hydrodynamics===

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 locomotion|undulatory]] to entirely [[oscillation|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.<ref name=Sfakiotakis>{{cite journal |author1=Sfakiotakis, M. |author2=Lane, D. M. |author3=Davies, J. B. C.  |date=1999 |url=http://www.mor-fin.com/Science-related-links_files/http___www.ece.eps.hw.ac.uk_Research_oceans_people_Michael_Sfakiotakis_IEEEJOE_99.pdf |title=Review of Fish Swimming Modes for Aquatic Locomotion |journal=IEEE Journal of Oceanic Engineering |volume=24 |issue=2 |pages=237–252 |doi=10.1109/48.757275 |bibcode=1999IJOE...24..237S |s2cid=17226211 |url-status=dead |archive-url=https://web.archive.org/web/20131224091124/http://www.mor-fin.com/Science-related-links_files/http___www.ece.eps.hw.ac.uk_Research_oceans_people_Michael_Sfakiotakis_IEEEJOE_99.pdf |archive-date=2013-12-24 }}</ref>

====Body-caudal fin====
[[File:Sardines.ogv|thumb|alt=Sardines swim in an aquarium tank.|[[Sardines]] use body-caudal fin propulsion to swim, holding their pectoral, dorsal, and anal fins flat against the body, creating a more [[streamlines, streaklines, and pathlines|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 termed [[fish locomotion#Body/caudal fin propulsion|body-caudal 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.<ref name=Sfakiotakis/><ref name=Blake>{{cite journal |author=Blake, R. W. |date=2004 |title=Review Paper: Fish functional design and swimming performance |journal=Journal of Fish Biology |volume=65 |issue=5 |pages=1193–1222 |doi=10.1111/j.0022-1112.2004.00568.x}}</ref>

===Adaptation===

Similar to adaptation in avian flight, swimming behaviors in fish can be thought of as a balance of stability and maneuverability.<ref name=Weihs>{{cite journal |last1=Weihs |first1=Daniel |year=2002 |title=Stability ''versus'' Maneuverability in Aquatic Locomotion |journal=Integrated and Computational Biology |volume=42 |issue=1 |pages=127–134 |doi=10.1093/icb/42.1.127 |pmid=21708701 |doi-access=free }}</ref> Because body-caudal fin swimming relies on more [[Anatomical terms of location#Anterior and posterior|caudal]] body structures that can direct powerful thrust only rearwards, this form of locomotion is particularly effective for accelerating quickly and cruising continuously.<ref name=Sfakiotakis/><ref name=Blake/> body-caudal fin 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 median-paired fin  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, median-paired fin swimming is well adapted for high maneuverability and is often seen in smaller fish that require elaborate escape patterns.<ref name=Weihs/>

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.<ref>{{cite journal |last1=Fulton |first1=C. J. |last2=Bellwood |first2=D. R. |last3=Wainwright |first3=P. C. |year=2005 |title=Wave energy and swimming performance shape coral reef fish assemblages |journal=Proceedings of the Royal Society B |volume=272 |issue=1565 |pages=827–832 |doi=10.1098/rspb.2004.3029 |pmid=15888415 |pmc=1599856 }}</ref>

Fish do not rely exclusively on one locomotor mode, but are rather locomotor generalists,<ref name=Sfakiotakis/> choosing among and combining behaviors from many available behavioral techniques. Predominantly body-caudal fin swimmers often incorporate movement of their [[Fish anatomy|pectoral, anal, and dorsal fins]] as an additional stabilizing mechanism at slower speeds,<ref>{{cite journal |last1=Heatwole |first1=S. J. |last2=Fulton |first2=C. J. |year=2013 |title=Behavioural flexibility in coral reef fishes responding to a rapidly changing environment |journal=Marine Biology |volume=160 |issue=3|pages=677–689 |doi=10.1007/s00227-012-2123-2|s2cid=85119253 }}</ref> but hold them close to their body at high speeds to improve [[Streamlines, streaklines, and pathlines|streamlining]] and reducing drag.<ref name=Sfakiotakis/> [[Zebrafish]] have even been observed to alter their locomotor behavior in response to changing hydrodynamic influences throughout growth and maturation.<ref name=McHenry>{{cite journal |last1=McHenry |first1=Matthew J. |last2=Lauder |first2=George V. |s2cid=33343483 |year=2006 |title=Ontogeny of Form and Function: Locomotor Morphology and Drag in Zebrafish (''Danio rerio'') |journal=Journal of Morphology |volume=267 |issue=9|pages=1099–1109 |doi=10.1002/jmor.10462 |pmid=16752407 }}</ref>