Editing Fish locomotion

{{short description|Ways that fish move around}}
[[File:Yellowfin tuna nurp.jpg|thumb|360px| Fish, like these [[yellowfin tuna]], use many different mechanisms to propel themselves through water]]
{{Use American English|date=December 2013}}

'''Fish locomotion''' is the various types of [[animal locomotion]] used by [[fish]], principally by [[aquatic locomotion|swimming]]. This is achieved in different groups of fish by a variety of mechanisms of propulsion, most often by wave-like lateral flexions of the fish's body and tail in the water, and in various specialised fish by motions of the [[fish fin|fin]]s. The major forms of locomotion in fish are:
* Anguilliform<!--don't link, this redirects here!-->, 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 specialized fish include movement by pectoral fins with a mainly stiff body, opposed sculling with dorsal and anal fins, as in the [[Molidae|sunfish]]; and movement by propagating a wave along the long fins with a motionless body, as in the [[Gymnotiformes|knifefish]] or [[Notopteridae|featherbacks]].

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 [[gliding flight|glide]] temporarily through the air.

==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====

<!--all these headings are redirect targets-->
[[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>

==Flight==
{{see also|flying fish|flying and gliding animals}}

The transition of predominantly swimming locomotion directly to flight has evolved in a single family of marine fish, the [[Flying fish|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 behaviors.<ref name=Fish90>Fish, F.E. (1990) Wing design and scaling of flying fish with regard to flight performance. "J. Zool. Lond." 221, 391-403.</ref><ref name=Fish91>Fish, Frank. (1991) On a Fin and a Prayer. "Scholars." 3(1), 4-7.</ref>

[[File:Schwalbenfisch.jpg|thumb|alt=flying fish.|[[Flying fish]] gain sufficient lift to glide above the water thanks to their enlarged pectoral fins.]]

===Tradeoffs===

While most fish have [[fish anatomy#Types of fin|caudal fin]]s with evenly sized lobes (i.e. homocaudal), flying fish have an enlarged [[anatomical terms of location|ventral]] lobe (i.e. hypocaudal) which facilitates dipping only a portion of the tail back onto the water for additional thrust production and steering.<ref name=Fish91/>

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.<ref name=Fish90/> 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 designs.<ref name=Fish90/>

===Biplane body plan===
In the [[biplane]] or ''[[Cypselurus]]'' body plan, both the pectoral and pelvic fins are enlarged to provide lift during flight.<ref name=Fish90/> 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.<ref name=Fish91/> As a result of this high lift production, these fish are excellent gliders and are well adapted for maximizing flight distance and duration.

Comparatively, ''[[Cypselurus]]'' flying fish have lower wing loading and smaller aspect ratios (i.e. broader wings) than their ''[[flying fish|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|"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 generation.<ref name=Fish90/>

[[File:Sailfin flyingfish.jpg|thumb|alt=illustration of a typical flying fish body plan|In the [[Cypselurus|monoplane body plan]] of ''[[flying fish|Exocoetus]]'', only the pectoral fins are abnormally large, while the pelvic fins are small.]]

===Monoplane body plan===
In the ''[[flying fish|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 ratio]]s (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).<ref name=Fish90/> 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.

==Walking==
{{main|Walking fish}}
[[File: Alticus arnoldorum hopping - pone.0011197.s007.ogv|thumb|220px|''Alticus arnoldorum'' hopping]]
[[File: Alticus arnoldorum climbing up a vertical piece of Plexiglas - pone.0011197.s009.ogv|thumb|220px|''Alticus arnoldorum'' climbing up a vertical piece of Plexiglas]]

A "walking fish" is a fish that is able to travel over [[ecoregion#Terrestrial|land]] for extended periods of time. Some other cases of nonstandard fish locomotion include fish "walking" along the [[seabed|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 [[mudskipper]]s are probably the best land-adapted of contemporary fish and are able to spend days moving about out of water and can even climb [[mangrove]]s, although to only modest heights.<ref>{{cite web |url=http://www.cairnsmuseum.org.au/tourism.htm |title=Cairns Museum Tour - Cairns-Kuranda Railway |access-date=2015-01-08 |url-status=dead |archive-url=https://web.archive.org/web/20150108041240/http://www.cairnsmuseum.org.au/tourism.htm |archive-date=2015-01-08 }}</ref> 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.<ref>{{Cite web |url=http://encarta.msn.com/encyclopedia_761564164/climbing_fish.html |title=Climbing Fish |access-date=2015-02-26 |archive-url=https://web.archive.org/web/20090829004031/http://encarta.msn.com/encyclopedia_761564164/Climbing_Fish.html |archive-date=2009-08-29 |url-status=dead }}</ref>

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]].<ref>[https://web.archive.org/web/20020714172535/http://news.nationalgeographic.com/news/2002/07/0712_020712_snakehead.html "Maryland Suffers Setback in War on Invasive Walking Fish"], ''National Geographic News''
July 12, 2002</ref> [[Bichir|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.<ref>[https://www.bbc.co.uk/nature/16251726 Shells, trees and bottoms: Strange places fish live]</ref><ref>{{cite news| url=https://www.reuters.com/article/us-fish-idUSN1522299020071115?pageNumber=1 | work=Reuters | title=Tropical fish can live for months out of water | date=15 November 2007}}</ref><ref>[https://web.archive.org/web/20071108211523/http://news.nationalgeographic.com/news/2007/11/071106-tree-fish.html Fish Lives in Logs, Breathing Air, for Months at a Time]</ref><ref>[https://web.archive.org/web/20071108225026/http://news.nationalgeographic.com/news/2007/11/071106-tree-fish_2.html Fish Lives in Logs, Breathing Air, for Months at a Time]</ref>

[[File:OgcocephalusParvus.jpg|thumb|left|''[[Ogcocephalus|Ogcocephalus parvus]]''|179x179px]]
There are some species of fish that can "walk" along the sea floor but not on land; one such animal is the [[Dactylopteridae|flying gurnard]] (it does not actually fly, and should not be confused with [[flying fish]]). The batfishes of the family [[Ogcocephalidae]] (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.<ref name="jonessulak">{{cite journal |last=Jones |first=AT |author2=KJ Sulak |title=First Central Pacific Plate and Hawaiian Record of the Deep-sea Tripod Fish ''Bathypterois grallator'' (Pisces: Chlorophthalmidae) |journal=Pacific Science |year=1990 |volume=44 |number=3 |pages=254–7 |url=http://scholarspace.manoa.hawaii.edu/bitstream/10125/1281/1/v44n3-254-257.pdf }}</ref> 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.
<ref>[https://www.bbc.co.uk/nature/16157835 Fish uses fins to walk and bound]</ref><ref>[http://www.pnas.org/content/early/2011/12/08/1118669109 Behavioral evidence for the evolution of walking and bounding before terrestriality in sarcopterygian fishes]</ref><ref>[https://www.sciencedaily.com/releases/2011/12/111212153117.htm A Small Step for Lungfish, a Big Step for the Evolution of Walking]</ref>

==Burrowing==
Many fishes, particularly eel-shaped fishes such as [[Anguillidae|true eels]], [[moray eels]], and [[Mastacembelidae|spiny eel]]s, are capable of [[burrow]]ing through sand or mud.<ref name="Monks">{{cite book | last = Monks| first = Neale  | title = Brackish-Water Fishes  | publisher = [[TFH Publications|TFH]]  | year = 2006  | pages = 223–226  | isbn = 978-0-7938-0564-8}}</ref> [[Ophichthidae|Ophichthids]], the snake eels, are capable of burrowing either forwards or backwards.<ref>{{cite book |last=Allen |first=Gerry |title=Marine Fishes of Southeast Asia: A Field Guide for Anglers and Divers |url=https://books.google.com/books?id=e9JGCgAAQBAJ&pg=PA56 |year=1999 |publisher=Tuttle Publishing |isbn=978-1-4629-1707-5 |page=56 |quote=many have a bony, sharp tail and are equally adept at burrowing forward or backward.}}</ref>

== In larvae ==

=== Swimming ===

[[File:Salmonlarvakils.jpg|thumb|Salmon larva emerging from its egg]]

Fish larvae, like many adult fishes, swim by undulating their body. The swimming speed varies proportionally with the size of the animals, in that smaller animals tend to swim at lower speeds than larger animals. The swimming mechanism is controlled by the flow regime of the larvae. [[Reynolds number]] (Re) is defined as the ratio of [[inertial force]] to [[viscosity|viscous force]]. Smaller organisms are affected more by viscous forces, like friction, and swim at a smaller Reynolds number. Larger organisms use a larger proportion of inertial forces, like pressure, to swim, at a higher Reynolds number.<ref name="Muller et al 2008">‘Flow Patterns Of Larval Fish: Undulatory Swimming in the Intermediate Flow Regime’ by Ulrike K. Müller, Jos G. M. van den Boogaart and Johan L. van Leeuwen. Journal of Experimental Biology 2008 211: 196–205; doi: 10.1242/jeb.005629</ref>

The larvae of ray finned fishes, the [[Actinopterygii]], swim at a quite large range of Reynolds number (Re ≈10 to 900). This puts them in an intermediate flow regime where both inertial and viscous forces play an important role. As the size of the larvae increases, the use of pressure forces to swim at higher Reynolds number increases.

Undulatory swimmers generally shed at least two types of wake: Carangiform swimmers shed connected vortex loops and Anguilliform swimmers shed individual vortex rings. These vortex rings depend upon the shape and arrangement of the trailing edge from which the vortices are shed. These patterns depend upon the swimming speed, ratio of swimming speed to body wave speed and the shape of body wave.<ref name="Muller et al 2008" />

A spontaneous bout of swimming has three phases. The first phase is the start or acceleration phase: In this phase the larva tends to rotate its body to make a 'C' shape which is termed the preparatory stroke. It then pushes in the opposite direction to straighten its body, which is called a propulsive stroke, or a power stroke, which powers the larva to move forward. The second phase is cyclic swimming. In this phase, the larva swims with an approximately constant speed. The last phase is deceleration. In this phase, the swimming speed of the larva gradually slows down to a complete stop. In the preparatory stroke, due to the bending of the body, the larva creates 4 vortices around its body, and 2 of those are shed in the propulsive stroke.<ref name="Muller et al 2008" /> Similar phenomena can be seen in the deceleration phase. However, in the vortices of the deceleration phase, a large area of elevated vorticity can be seen compared to the starting phase.

The swimming abilities of larval fishes are important for survival. This is particularly true for the larval fishes with higher metabolic rate and smaller size which makes them more susceptible to predators. The swimming ability of a reef fish larva helps it to settle at a suitable reef and for locating its home as it is often isolated from its home reef in search of food. Hence the swimming speed of reef fish larvae are quite high (≈12&nbsp;cm/s - 100&nbsp;cm/s) compared to other larvae.<ref name="Fisher et al 2005">"Critical Swimming Speeds of Late-Stage Coral Reef Fish Larvae: Variation within Species, Among Species and Between Locations" by Fisher, R., Leis, J.M., Clark, D.L.in Marine Biology (2005) 147: 1201. https://doi.org/10.1007/s00227-005-0001-x,</ref><ref>"Development of Swimming Abilities in Reef Fish Larvae" by Rebecca Fisher, David R. Bellwood, Suresh D. Job in Marine Ecology-progress Series - MAR ECOL-PROGR SER. 202. 163-173. 10.3354/meps202163</ref> The swimming speeds of larvae from the same families at the two locations are relatively similar.<ref name="Fisher et al 2005" /> However, the variation among individuals is quite large. At the species level, length is significantly related to swimming ability. However, at the family level, only 16% of variation in swimming ability can be explained by length.<ref name="Fisher et al 2005" /> There is also a negative correlation between the [[fineness ratio]] (length of body to maximum width) and the swimming ability of reef fish larvae. This suggests a minimization of overall drag and maximization of volume. Reef fish larvae differ significantly in their critical swimming speed abilities among taxa which leads to high variability in sustainable swimming speed.<ref>‘Maximum Sustainable Swimming Speeds Of Late-Stage Larvae Of Nine Species Of Reef Fishes’ by Rebecca Fisher, Shaun K.Wilson in Journal of Experimental Marine Biology and Ecology, Volume 312, Issue 1, 2004, Pages 171–186, ISSN 0022-0981, https://doi.org/10.1016/j.jembe.2004.06.009</ref> This again leads to sustainable variability in their ability to alter dispersal patterns, overall dispersal distances and control their temporal and spatial patterns of settlement.<ref>'Development of Swimming Abilities in Reef Fish Larvae' by Rebecca Fisher, David R. Bellwood, Suresh D. Job in Marine Ecology-progress Series - MAR ECOL-PROGR SER. 202. 163-173. 10.3354/meps202163</ref>

=== Hydrodynamics ===

Small undulatory swimmers such as fish larvae experience both inertial and viscous forces, the relative importance of which is indicated by Reynolds number (Re). Reynolds number is proportional to body size and swimming speed. The swimming performance of a larva increases between 2–5 days post fertilization. Compared with adults, larval fish experience relatively high viscous force. To enhance thrust to an equal level with the adults, it increases its tail beat frequency and thus amplitude. In zebrafish, tail beat frequency increases over larval age to 95&nbsp;Hz in 3 days post fertilization from 80&nbsp;Hz in 2 days post fertilization. This higher frequency leads to higher swimming speed, thus reducing predation and increasing prey catching ability when they start feeding at around 5 days post fertilization. The vortex shedding mechanics changes with the flow regime in an inverse non-linear way. Strouhal number is a design parameter for the vortex shedding mechanism. It can be defined as a ratio of the product of tail beat frequency with amplitude with the mean swimming speed.<ref name="van Leeuwen Voesenek Müller 2015">{{cite journal |last1=van Leeuwen |first1=Johan L. |last2=Voesenek |first2=Cees J. |last3=Müller |first3=Ulrike K. |title=How body torque and Strouhal number change with swimming speed and developmental stage in larval zebrafish |journal=Journal of the Royal Society Interface |publisher=The Royal Society |volume=12 |issue=110 |year=2015 |issn=1742-5689 |doi=10.1098/rsif.2015.0479 |page=20150479|pmid=26269230 |pmc=4614456 |doi-access=free }}</ref> Reynolds number (Re) is the main deciding criteria of a flow regime. It has been observed over different type of larval experiments that, slow larvae swims at higher Strouhal number but lower Reynolds number. However, the faster larvae swims distinctively at opposite conditions, that is, at lower Strouhal number but higher Reynolds number. Strouhal number is constant over similar speed ranged adult fishes. Strouhal number does not only depend on the small size of the swimmers, but also dependent to the flow regime. As in fishes which swim in viscous or high-friction flow regime, would create high body drag which will lead to higher Strouhal number. Whereas, in high viscous regime, the adults swim at lower stride length which leads to lower tail beat frequency and lower amplitude. This leads to higher thrust for same displacement or higher propulsive force, which unanimously reduces the Reynolds number.<ref>'How body torque and Strouhal number change with swimming speed and developmental stage in larval zebrafish' by Johan L. van Leeuwen, Cees J. Voesenek and Ulrike K. Müller in J. R. Soc. Interface 2015 12 20150479; DOI: 10.1098/rsif.2015.0479. 6 September 2015</ref>

Larval fishes start feeding at 5–7 days post fertilization. And they experience extreme mortality rate (≈99%) in the few days after feeding starts. The reason for this 'Critical Period' (Hjort-1914) is mainly hydrodynamic constraints. Larval fish fail to eat even if there are enough prey encounters. One of the primary determinants of feeding success is the size of larval body. The smaller larvae function in a lower Reynolds number (Re) regime. As the age increases, the size of the larvae increases, which leads to higher swimming speed and  increased Reynolds number. It has been observed through many experiments that the Reynolds number of successful strikes (Re~200) is much higher than the Reynolds number of failed strikes (Re~20).<ref name="China Holzman 2014">{{cite journal |last1=China |first1=Victor |last2=Holzman |first2=Roi |title=Hydrodynamic starvation in first-feeding larval fishes |journal=Proceedings of the National Academy of Sciences |volume=111 |issue=22 |date=19 May 2014 |issn=0027-8424 |doi=10.1073/pnas.1323205111 |pages=8083–8088|pmid=24843180 |pmc=4050599 |bibcode=2014PNAS..111.8083C |doi-access=free }}</ref><ref name="China Levy Liberzon Elmaliach 2017">{{cite journal |last1=China |first1=Victor |last2=Levy |first2=Liraz |last3=Liberzon |first3=Alex |last4=Elmaliach |first4=Tal |last5=Holzman |first5=Roi |title=Hydrodynamic regime determines the feeding success of larval fish through the modulation of strike kinematics |journal=Proceedings of the Royal Society B: Biological Sciences |publisher=The Royal Society |volume=284 |issue=1853 |date=26 April 2017 |issn=0962-8452 |doi=10.1098/rspb.2017.0235 |page=20170235|pmid=28446697 |pmc=5413926 |doi-access=free }}</ref> Numerical analysis of suction feeding at a low Reynolds number concluded that around 40% energy invested in mouth opening is lost to frictional forces rather than contributing to accelerating the fluid towards mouth.<ref name="The Royal Society 1988">{{cite journal |title=A quantitative hydrodynamical model of suction feeding in larval fishes: the role of frictional forces |journal=Proceedings of the Royal Society of London. Series B. Biological Sciences |publisher=The Royal Society |volume=234 |issue=1276 |date=23 August 1988 |issn=0080-4649 |doi=10.1098/rspb.1988.0048 |pages=263–281|bibcode=1988RSPSB.234..263D |last1=Drost |first1=M. R. |last2=Muller |first2=M. |last3=Osse |first3=J. W. M. |s2cid=86188901 }}</ref> Ontogenetic improvement in the sensory system, coordination and experiences are non-significant relationship while determining feeding success of larvae <ref name="China Levy Liberzon Elmaliach 2017"/> A successful strike positively depends upon the peak flow speed or the speed of larvae at the time of strike. The peak flow speed is also dependent on the gape speed or the speed of opening the buccal cavity to capture food. As the larva ages, its body size increase and its gape speed also increase, which cumulatively increase the successful strike outcomes.<ref name="China Levy Liberzon Elmaliach 2017"/> 

The ability of a larval prey to survive an encounter with predator totally depends on its ability to sense and evade the strike. Adult fishes exhibit rapid suction feeding strikes as compared to larval fishes. Sensitivity of larval fish to velocity and flow fields provides the larvae a critical defense against predation. Though many prey use their visual system to detect and evade predators when there is light, it is hard for the prey to detect predators at night, which leads to a delayed response to the attack. There is a mechano-sensory system in fishes to identify the different flow generated by different motion surrounding the water and between the bodies called as lateral line system.<ref name="Stewart Cardenas McHenry 2013">{{cite journal |last1=Stewart |first1=William J. |last2=Cardenas |first2=Gilberto S. |last3=McHenry |first3=Matthew J. |title=Zebrafish larvae evade predators by sensing water flow |journal=Journal of Experimental Biology |publisher=The Company of Biologists |volume=216 |issue=3 |date=1 February 2013 |issn=1477-9145 |doi=10.1242/jeb.072751 |pages=388–398|pmid=23325859 |doi-access=free }}</ref> After detecting a predator, a larva evades its strike by 'fast start' or 'C' response. A swimming fish disturbs a volume of water ahead of its body with a flow velocity that increases with the proximity to the body. This particular phenomenon is sometimes called a [[bow wave]].<ref name="Ferry-Graham Wainwright Lauder 2003">{{cite journal |last1=Ferry-Graham |first1=Lara A. |last2=Wainwright |first2=Peter C. |last3=Lauder |first3=George V. |title=Quantification of flow during suction feeding in bluegill sunfish |journal=Zoology |publisher=Elsevier |volume=106 |issue=2 |year=2003 |issn=0944-2006 |doi=10.1078/0944-2006-00110 |pages=159–168|pmid=16351901 }}</ref> The timing of the 'C' start response affects escape probability inversely. Escape probability increases with the distance from the predator at the time of strike. In general, prey successfully evade a predator strike from an intermediate distance (3–6&nbsp;mm) from the predator.<ref name="Stewart Cardenas McHenry 2013"/> 

<gallery mode="packed" caption="Larvae of different fishes">
File:Clupeaharenguskils2.jpg|[[Atlantic herring]] eggs, with a newly hatched larva
File:Clupealarvamatchkils.jpg|Freshly hatched herring larva in a drop of water compared to a match head.
File:Lanternfish larva.jpg|Late stage [[lanternfish]] larva
File:Arnoglossus laterna larva.jpg|A 9mm long late stage [[scaldfish]] larva
File:LeptocephalusConger.jpg|Larva of a conger eel, 7.6&nbsp;cm
File:Larval stage of bluefin tuna.jpg|[[Bluefin tuna]] larva
File:Pacific cod larvae.jpg|[[Pacific cod]] larva
File:Walleye larva (8740460659).jpg|[[Walleye]] larva
File:Common sturgeon larva.jpg|[[Common sturgeon]] larva
File:FMIB 47039 Ostracion hoops.jpeg|[[Boxfish]] larva
File:Molalavdj.jpg|[[Ocean sunfish]] larva, 2.7mm
</gallery>

===Behavior===

Objective quantification is complicated in higher vertebrates by the complex and diverse locomotor repertoire and neural system. However, the relative simplicity of a juvenile brain and simple nervous system of fishes with fundamental neuronal pathways allows zebrafish larvae to be an apt model to study the interconnection between locomotor repertoire and neuronal system of a vertebrate. Behavior represents the unique interface between intrinsic and extrinsic forces that determine an organism's health and survival.<ref name="Larval Zebrafish 2008">‘Locomotion In Larval Zebrafish: Influence of Time of Day, Lighting and Ethanol’ by R.C. MacPhail, J. Brooks, D.L. Hunter, B. Padnos a, T.D. Irons, S. Padilla in Neurotoxicology. 30. 52-8. 10.1016/j.neuro.2008.09.011.</ref> Larval zebrafish perform many locomotor behavior such as escape response, prey tracking, optomotor response etc. These behaviors can be categorized with respect to body position as ‘C’-starts, ‘J’-turns, slow scoots, routine turns etc. Fish larvae respond to abrupt changes in illumination with distinct locomotor behavior. The larvae show high locomotor activity during periods of bright light compared to dark. This behavior can direct towards the idea of searching food in light whereas the larvae do not feed in dark.<ref name="ReferenceA">‘Modulation of Locomotor Activity in Larval Zebrafish During Light Adaptation’ by Harold A. Burgess and Michael Granato. In Journal of Experimental Biology 2007 210: 2526–2539; doi: 10.1242/jeb.003939</ref> Also light exposure directly manipulates the locomotor activities of larvae throughout circadian period of light and dark with higher locomotor activity in light condition than in dark condition which is very similar as seen in mammals. Following the onset of darkness, larvae shows hyperactive scoot motion prior to a gradual drop off. This behavior could possibly be linked to find a shelter before nightfall. Also larvae can treat this sudden nightfall as under debris and the hyperactivity can be explained as the larvae navigation back to illuminated areas.<ref name="ReferenceA"/> Prolonged dark period can reduce the light-dark responsiveness of larvae. Following light extinction, larvae execute large angle turns towards the vanished light source, which explains the navigational response of a larva.<ref name="ReferenceA"/> Acute ethanol exposure reduce visual sensitivity of larvae causing a latency to respond in light and dark period change.<ref name="Larval Zebrafish 2008"/>

==See also==
* {{annotated link|Aquatic locomotion}}
* [[Microswimmer]]
* {{annotated link|Role of skin in locomotion}}
* {{annotated link|Tradeoffs for locomotion in air and water}}
* {{annotated link|Undulatory locomotion}}

==References==
{{reflist}}

==Further reading==
{{refbegin|2}}
* [[R. McNeill Alexander|Alexander, R. McNeill]] (2003) ''Principles of Animal Locomotion.'' Princeton University Press. {{ISBN|0-691-08678-8}}.
* {{cite journal | last1 = Eloy | first1 = Christophe | year = 2013 | title = On the best design for undulatory swimming | journal = Journal of Fluid Mechanics | volume = 717 | pages = 48–89 | doi = 10.1017/jfm.2012.561 | bibcode = 2013JFM...717...48E | s2cid = 56438579 }}
* {{cite journal | last1 = Lauder | first1 = GV | author-link = George V. Lauder (biologist) | last2 = Nauen | first2 = JC | last3 = Drucker | first3 = EG | year = 2002 | title = Experimental Hydrodynamics and Evolution: Function of Median Fins in Ray-finned Fishes | journal = Integr. Comp. Biol. | volume = 42 | issue = 5| pages = 1009–1017 | doi = 10.1093/icb/42.5.1009 | pmid = 21680382 | doi-access = free }}
* Videler JJ (1993) [https://books.google.com/books?id=qTm_EWMlUH8C&pg=PR11 ''Fish Swimming''] Springer. {{ISBN|9780412408601}}.
* Vogel, Steven (1994) ''Life in Moving Fluid: The Physical Biology of Flow.'' Princeton University Press. {{ISBN|0-691-02616-5}} (particularly pp.&nbsp;115–117 and pp.&nbsp;207–216 for specific biological examples swimming and flying respectively)
* Wu, Theodore, Y.-T., Brokaw, Charles J., Brennen, Christopher, Eds. (1975) ''Swimming and Flying in Nature''. Volume 2, Plenum Press. {{ISBN|0-306-37089-1}} (particularly pp.&nbsp;615–652 for an in depth look at fish swimming)
{{refend}}

== External links ==
* [http://www.thefreelibrary.com/How+fish+swim:+study+solves+muscle+mystery-a014133436 How fish swim: study solves muscle mystery]
* [https://web.archive.org/web/20120227032707/http://www.villalachouette.de/william/krims/YoFisch/ Simulated fish locomotion]
*[https://web.archive.org/web/20121210132917/http://www.nmri.go.jp/eng/khirata/fish/general/principle/index_e.html Basic introduction to the basic principles of biologically inspired swimming robots]
* [https://web.archive.org/web/20110724192433/http://www.geol.umd.edu/~jmerck/bsci392/lecture10/lecture10.html The biomechanics of swimming]

{{diversity of fish|state=expanded}}
{{fins, limbs and wings}}

[[Category:Ichthyology]]
[[Category:Aquatic locomotion]]
[[Category:Animal locomotion]]
[[Category:Articles containing video clips]]