View source for Biology:Fish fin

{{Short description|Bony skin-covered spines or rays protruding from the body of a fish}}
[[File:Lampanyctodes hectoris (fins).png|thumb|right|400px|{{center|1=Ray fins on a [[Biology:Teleost|teleost fish]], [[Biology:Hector's lanternfish|Hector's lanternfish]]<br/>
(1) pectoral fins (paired), (2) [[Biology:Pelvic fin|pelvic fin]]s (paired), (3) dorsal fin,<br />(4) adipose fin, (5) anal fin, (6) caudal (tail) fin}}]]

'''Fins''' are moving [[Biology:Appendage|appendage]]s protruding from the body of [[Biology:Fish|fish]] that interact with water to generate [[Thrust|thrust]] and help the fish [[Biology:Aquatic locomotion|swim]]. Apart from the [[Biology:Tail|tail]] or caudal fin, fish fins have no direct connection with the [[Biology:Vertebral column|spine]] and are supported only by [[Biology:Muscle|muscle]]s.

Fish fins are distinctive anatomical features with varying structures among different [[Biology:Clade|clade]]s: in [[Biology:Ray-finned fish|ray-finned fish]] ([[Biology:Actinopterygii|Actinopterygii]]), fins are mainly composed of [[Biology:Bone|bony]] spines or rays covered by a thin stretch of [[Biology:Fish scale|scale]]less [[Biology:Skin|skin]]; in [[Biology:Lobe-finned fish|lobe-finned fish]] ([[Biology:Sarcopterygii|Sarcopterygii]]) such as [[Biology:Coelacanth|coelacanth]]s and [[Biology:Lungfish|lungfish]], fins are short rays based around a muscular central [[Biology:Limb bud|bud]] supported by bones; in cartilaginous fish (Chondrichthyes) and jawless fish ([[Biology:Agnatha|Agnatha]]), fins are fleshy "[[Biology:Flipper (anatomy)|flipper]]s" supported by a cartilaginous skeleton.

Fins at different locations on the fish serve different purposes, and are divided into two groups: the midsagittal ''unpaired fins'' and the more laterally located ''paired fins''. Unpaired fins are predominantly associated with generating linear acceleration via [[Biology:Fish locomotion#Body/caudal fin propulsion|oscillating propulsion]], as well as providing [[Physics:Directional stability|directional stability]]; while paired fins are used for generating [[Biology:Fish locomotion#Median/paired fin propulsion|paddling acceleration]], deceleration, and differential thrust or [[Physics:Lift (force)|lift]] for [[Physics:Yaw (rotation)|turning]], surfacing or diving and rolling. Fins can also be used for other locomotions other than swimming, for example, [[Biology:Flying fish|flying fish]] use pectoral fins for [[Biology:Gliding flight|gliding flight]] above water surface, and [[Biology:Frogfish|frogfish]] and many [[Biology:Amphibious fish|amphibious fish]]es use pectoral and/or pelvic fins for crawling. Fins can also be used for other purposes: [[Biology:Remora|remora]]s and gobies have [[Physics:Suction cup|sucker]]-like fins for attaching to surfaces; male [[Biology:Shark|shark]]s and [[Biology:Mosquitofish|mosquitofish]] use a modified fin to deliver sperm; [[Biology:Thresher shark|thresher shark]]s use their caudal fin to whip and stun prey; reef stonefish have spines in their dorsal fins that inject [[Biology:Venom|venom]] as an anti-predator defense; [[Biology:Anglerfish|anglerfish]] use the first spine of their dorsal fin like a [[Engineering:Fishing rod|fishing rod]] to lure prey; and [[Biology:Triggerfish|triggerfish]] avoid predators by squeezing into coral crevices and using spines in their fins to anchor themselves in place.
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==Types of fins==
Fins can either be '''paired''' or '''unpaired'''. The pectoral and pelvic fins are paired, whereas the dorsal, anal and caudal fins are unpaired and situated along the midline of the body. For every type of fin, there are a number of fish [[Biology:Species|species]] in which this particular fin has been lost during evolution (e.g. pelvic fins in {{extinct}}''[[Biology:Bobasatrania|Bobasatrania]]'', caudal fin in ocean sunfish). In some clades, additional unpaired fins were acquired during evolution (e.g. additional dorsal fins, adipose fin). In some {{extinct}}[[Biology:Acanthodii|Acanthodii]] ("spiny sharks"), one or more pairs of "intermediate" or "prepelvic" spines are present between the pectoral and pelvic fins, but these are not associated with fins.

{| class="wikitable"
|-
! Pectoral fins<br /><small>(Arm fins)</small>
| [[File:Kopie van DSC00282.JPG|140px]]
| valign=top | {{anchor|AnchPectoral}} The paired '''pectoral fins''' are located on each side, usually kept folded just behind the operculum, and are [[Biology:Homology|homologous]] to the forelimbs of quadrupedal [[Biology:Tetrapod|tetrapod]]s or the upper limbs of bipedal tetrapods.
* 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 [[Biology:Shark|shark]]s, in maintaining depth and also enables the "[[Biology:Fish locomotion#Flight|flight]]" for [[Biology:Flying fish|flying fish]]
* In many fish, the pectoral fins aid in [[Biology:Fish locomotion#Walking|walking]], especially in the lobe-like fins of some anglerfish and in the [[Biology:Mudskipper|mudskipper]] (see also [[Biology:Walking fish|walking fish]])
* Certain rays of the pectoral fins may be adapted into finger-like projections, such as in [[Biology:Sea robin|sea robin]]s and [[Biology:Flying gurnard|flying gurnard]]s
* In [[Biology:Skate (fish)|skates]] and rays, the pectoral fins are used for propulsion (rajiform propulsion)
** The "horns" of [[Biology:Manta ray|manta ray]]s and their relatives are called '''cephalic fins'''; this is actually a modification of the anterior portion of the pectoral fin
|-
! [[Biology:Pelvic fin|Pelvic / Ventral fin]]s<br /><small>(Belly fins)</small>
| [[File:Barb gonio 080526 9681 ltn Pv.jpg|140px]]
| valign=top | {{anchor|AnchVentral}} The paired '''pelvic''' or '''ventral fins''' are the belly fins ({{ety|la|venter|belly}}) are typically located ventrally below and behind the pectoral fins, although in many fish families they may be positioned in front of the pectoral fins (e.g. cods). They are [[Biology:Homology|homologous]] to the hindlimbs of quadrupedal [[Biology:Tetrapod|tetrapod]]s or the lower limbs of bipedal tetrapods.
The pelvic fin assists the fish in going up or down through the water, turning sharply, and stopping quickly.
* In [[Biology:Goby|gobies]], the pelvic fins are often fused into a single sucker disk. This can be used to attach to objects<ref>{{cite journal | last1 = Standen | first1 = EM | year = 2009 | title = Muscle activity and hydrodynamic function of pelvic fins in trout ''(Oncorhynchus mykiss)'' | journal = The Journal of Experimental Biology | volume = 213 | issue = 5| pages = 831–841 | doi = 10.1242/jeb.033084 | pmid=20154199| doi-access = free }}</ref>
* Pelvic fins can take many positions along the ventral surface of the fish.  The ancestral ''abdominal'' position is seen in (for example) the [[Biology:Cyprinidae|minnows]]; the ''thoracic'' position in [[Biology:Centrarchidae|sunfish]]; and the ''jugular'' position, when the pelvics are anterior to the pectoral fins, as seen in the [[Biology:Burbot|burbot]]<ref>Gene Helfman, Bruce Collette, Douglas Facey, & Brian Bowen. (2009) The Diversity of Fishes: biology, evolution, and ecology. John Wiley & Sons.</ref>
|-
! style="width:90px" | Dorsal fin<br /><small>(Spinal fins)</small>
| [[File:Aileron de requin.jpg|140px]]{{center|1=<small>Dorsal fin of a shark</small>}}
| valign=top | {{anchor|AnchDorsal}} [[File:Dorsal fin 01.jpg|thumb|120px|Dorsal fin of a chub (''[[Biology:Squalius cephalus|Squalius cephalus]]'')]]
The '''dorsal fins''' are located on the back. A fish can have up to three dorsal fins. The dorsal fins serve to protect the fish against rolling, and assist it in sudden turns and stops.
* In [[Biology:Anglerfish|anglerfish]], the anterior of the dorsal fin is modified into an '''illicium''' and '''esca''', a biological equivalent to a fishing [[Engineering:Fishing rod|rod]] and [[Engineering:Fishing lure|lure]]
* The bones that support the dorsal fin are called ''pterygiophores''. There are two to three of them: "proximal" (axonosts), "middle" (baseosts), and "distal". In rock-hard, spinous fins the distal pterygiophores are often fused to the middle ones, or not present at all
* ''[[Biology:Gymnarchus|Gymnarchus]]'' uses only its dorsal fin for propulsion
* Boxfish, pufferfish and ocean sunfish use their dorsal fin in combination with their anal fin for propulsion ([[Biology:Fish locomotion#Tetraodontiform|tetraodontiform]] propulsion)
|-
! Anal/cloacal fin
| [[File:Barb gonio 080526 9660 ltn Af.jpg|140px]]
| valign=top | {{anchor|AnchAnal}} The '''anal/cloacal fin''' is located on the [[Biology:Anatomical terms of location|ventral]] surface behind the [[Biology:Anus|anus]]/[[Biology:Cloaca|cloaca]]. 
* The bones that support the anal fin are called ''pterygiophores''. There are up to two series, a proximal series (axonosts) and a distal series (baseosts)
* Most fish use their anal fin to stabilize while swimming
* [[Biology:Gymnotiformes|Knifefish]] use their anal fins for thrust (gymnotiform propulsion)
* Boxfish, pufferfish and ocean sunfish use their anal fin in combination with their dorsal fin for propulsion ([[Biology:Fish locomotion#Tetraodontiform|tetraodontiform]] propulsion)
|-
! Adipose fin
| [[File:Adipose fin 01.jpg|140px]]{{center|1=<small>Adipose fin of a trout</small>}}
| valign=top | {{anchor|AnchAdipose}} The '''adipose fin''' is a soft, fleshy fin found on the back behind the dorsal fin and just forward of the caudal fin. It is absent in many fish families, but found in nine of the 31 euteleostean orders ([[Biology:Percopsiformes|Percopsiformes]], [[Biology:Myctophiformes|Myctophiformes]], [[Biology:Aulopiformes|Aulopiformes]], [[Biology:Stomiiformes|Stomiiformes]], [[Biology:Salmoniformes|Salmoniformes]], [[Biology:Osmeriformes|Osmeriformes]], [[Biology:Characiformes|Characiformes]], Siluriformes and [[Biology:Argentiniformes|Argentiniformes]]).<ref name=Bender2013 /> Famous representatives of these orders are salmon, characids and [[Biology:Catfish|catfish]].

The function of the adipose fin is something of a mystery. It is frequently clipped off to mark hatchery-raised fish, though data from 2005 showed that trout with their adipose fin removed have an 8% higher tailbeat frequency.<ref>{{cite journal|last=Tytell|first=E.|title=The Mysterious Little Fatty Fin|journal=Journal of Experimental Biology|year=2005|volume=208|issue=1|pages=v-vi|doi=10.1242/jeb.01391|doi-access=free}}</ref><ref>{{cite journal|last=Reimchen|first=T E|author2=Temple, N F|title=Hydrodynamic and phylogenetic aspects of the adipose fin in fishes|journal=Canadian Journal of Zoology|year=2004|volume=82|issue=6|pages=910–916|doi=10.1139/Z04-069|url=http://eprints.uwe.ac.uk/38870/}}</ref>  Additional information released in 2011 has suggested that the fin may be vital for the detection of, and response to, stimuli such as touch, sound and changes in pressure. Canadian researchers identified a neural network in the fin, indicating that it likely has a sensory function, but are still not sure exactly what the consequences of removing it are.<ref>{{cite news|last=Temple|first=Nicola|title=Removal of trout, salmon fin touches a nerve|url=http://www.cosmosmagazine.com/news/removal-trout-salmon-fin-touches-a-nerve/|newspaper=Cosmos|date=18 July 2011|url-status=dead|archive-url=https://web.archive.org/web/20140112084221/http://www.cosmosmagazine.com/news/removal-trout-salmon-fin-touches-a-nerve/|archive-date=12 January 2014}}</ref><ref>{{cite journal|last=Buckland-Nicks|first=J. A.|author2=Gillis, M.|author3=Reimchen, T. E.|title=Neural network detected in a presumed vestigial trait: ultrastructure of the salmonid adipose fin|journal=Proceedings of the Royal Society B: Biological Sciences|year=2011|volume=279|issue=1728|pages=553–563|doi=10.1098/rspb.2011.1009|pmid=21733904|pmc=3234561}}</ref>

A comparative study in 2013 indicates the adipose fin can develop in two different ways. One is the salmoniform-type way, where the adipose fin develops from the larval-fin fold at the same time and in the same direct manner as the other median fins. The other is the characiform-type way, where the adipose fin develops late after the larval-fin fold has diminished and the other median fins have developed. They claim the existence of the characiform-type of development suggests the adipose fin is not "just a larval fin fold remainder" and is inconsistent with the view that the adipose fin lacks function.<ref name=Bender2013>{{Cite journal|last1=Bender|first1=Anke|last2=Moritz|first2=Timo|date=2013-09-01|title=Developmental residue and developmental novelty – different modes of adipose-fin formation during ontogeny|journal=Zoosystematics and Evolution|language=en|volume=89|issue=2|pages=209–214|doi=10.1002/zoos.201300007|issn=1860-0743}}</ref>

Research published in 2014 indicates that the adipose fin has [[Biology:Convergent evolution|evolved repeatedly in separate lineages]].<ref>{{cite journal|last=Stewart|first=Thomas A.|author2=Smith, W. Leo|author3=Coates, Michael I. |title=The origins of adipose fins: an analysis of homoplasy and the serial homology of vertebrate appendages|journal=Proceedings of the Royal Society B: Biological Sciences|year=2014|volume=281|issue=1781|pages=20133120|doi=10.1098/rspb.2013.3120|pmid=24598422|pmc=3953844}}</ref>

|-
! Caudal fin<br /><small>(Tail fin)</small>
| [[File:PletwyRyb.svg|140px]]<br /><br />140px{{center|1=<small>Heterocercal caudal fin (A)</small>}}<br /><br />[[File:Barb gonio 080525 9610 ltn Cf.jpg|140px]]{{center|1=<small>Homocercal caudal fin (C)</small>}}
| valign=top | {{anchor|AnchCaudal}} The '''caudal fin''' is the tail fin (from the Latin ''cauda'' meaning tail), located at the end of the caudal peduncle. It is used for propulsion in most taxa (see also body-caudal fin locomotion). The tail fin is supported by the vertebrae of the [[Biology:Axial skeleton|axial skeleton]] and pterygiophores (radials). Depending on the relationship with the axial skeleton, four types of caudal fins (A-D) are distinguished:

(A) - '''Heterocercal''' means the vertebrae extend into the upper lobe of the tail, often making it longer than the lower lobe (as in [[Biology:Shark|shark]]s, {{extinct}}[[Biology:Placodermi|Placodermi]], most [[Biology:Stem group|stem]] [[Biology:Actinopterygii|Actinopterygii]], and [[Biology:Acipenseriformes|sturgeons and paddlefish]]). However, the external shape of heterocercal tail fins can also appear symmetric (e.g. {{extinct}}''[[Biology:Birgeria|Birgeria]]'', {{extinct}}''[[Biology:Bobasatrania|Bobasatrania]]''). Heterocercal is the opposite of hypocercal
:* '''Hypocercal''', also known as '''reversed heterocercal''', means that the vertebrae extend into the lower lobe of the tail, making it longer than the upper lobe (as in the {{extinct}}[[Biology:Anaspida|Anaspida]]). It is the opposite of heterocercal.<ref>{{cite book |last1=Hyman |first1=Libbie |title=Hyman's Comparative Vertebrate Anatomy |date=1992 |publisher=The University of Chicago Press |isbn=978-0226870137 |page=210 |edition=3 |url=https://books.google.com/books?id=VKlWjdOkiMwC&q=reverse+heterocercal+tail&pg=PA210 |access-date=18 October 2018}}</ref>
:* '''Hemiheterocercal''' refers to a condition that is intermediate between heterocercal and homocercal (see below), where the vertebrae do not extend to the tip the upper lobe (e.g. in [[Biology:Stem group|stem]] [[Biology:Neopterygii|Neopterygii]])<ref name="Brough1936">{{cite journal|last=Brough |first=James |title=On the evolution of bony fishes during the Triassic Period |journal=Biological Reviews |year=1936 |volume=11 |issue=3 |pages=385–405 |doi=10.1111/j.1469-185X.1936.tb00912.x|s2cid=84992418 }}</ref>

(B) - '''Protocercal''' means the vertebrae extend to the tip of the tail and the tail is symmetrical but not expanded (as in the first fishes and the cyclostomes, and a more primitive precursor in lancelets)

(C) - '''Homocercal''' where the fin usually appears superficially symmetric but in fact the vertebrae extend for a very short distance into the upper lobe of the fin. Homocercal caudal fins can, however, also appear asymmetric (e.g. [[Biology:Exocoetus volitans|blue flying fish]]). Most modern fishes ([[Biology:Teleost|teleost]]s) have a homocercal tail. These come in a variety of shapes, and can appear:
:* '''rounded''' or '''pointed''' (e.g. [[Biology:Round goby|round goby]])
:* '''truncated''', ending in a more-or-less vertical edge (e.g. [[Biology:Trout|trout]])
:* '''emarginate''', ending with a slight inward curve (e.g. [[Biology:Eurasian carp|Eurasian carp]])
:* '''forked''', ending in two prongs (e.g. [[Biology:Catla|catla]])
:* '''lunate''' or shaped like a crescent moon (e.g. [[Biology:Swordfish|swordfish]])

(D) - '''Diphycercal''' means the vertebrae extend to the tip of the tail and the tail is symmetrical and expanded (as in the [[Biology:Bichir|bichir]], [[Biology:Lungfish|lungfish]], [[Biology:Lamprey|lamprey]], [[Biology:Coelacanth|coelacanth]]s and {{extinct}}Tarrasiiformes). Most Palaeozoic fishes had a diphycercal heterocercal tail.<ref>von Zittel KA, Woodward AS and Schlosser M (1932) ''Text-book of Paleontology'' Volume 2, Macmillan and Company. Page 13.</ref>
:* '''Abbreviate diphycercal''' is a diphycercal fin with a short base ({{extinct}}[[Biology:Saurichthyiformes|Saurichthyiformes]])<ref name="Brough1936"/><ref>{{cite journal | author = Kogan , Romano  | year = 2016 | title = Redescription of ''Saurichthys madagascariensis'' Piveteau, 1945 (Actinopterygii, Early Triassic), with implications for the early saurichthyid morphotype | journal = Journal of Vertebrate Paleontology | volume = 36 | issue = 4| page = e1151886 | doi = 10.1080/02724634.2016.1151886 | bibcode = 2016JVPal..36E1886K | s2cid = 87234436 }}</ref>
|-
! Caudal keel<br /><br /><br />Finlets {{anchor|AnchFinlet}}
| [[File:Thunnus obesus (Bigeye tuna) diagram cropped.GIF|140px]]
| valign=top | {{anchor|AnchCaudal keel}} Some types of fast-swimming fish have a horizontal '''caudal keel''' just forward of the tail fin. Much like the [[Engineering:Keel|keel]] of a ship, this is a lateral ridge on the caudal peduncle, usually composed of scutes (see below), that provides stability and support to the caudal fin. There may be a single paired keel, one on each side, or two pairs above and below.

'''Finlets''' are small fins, generally behind the dorsal and anal fins (in [[Biology:Bichir|bichir]]s, there are only finlets on the dorsal surface and no dorsal fin). In some fish such as [[Biology:Tuna|tuna]] or sauries, they are rayless, non-retractable, and found between the last dorsal and/or anal fin and the caudal fin.
|}

==Bony fishes==
[[File:Lingcodskeleton1600ppx.JPG|thumb|250px|right|Skeleton of a [[Biology:Lingcod|lingcod]], a ray-finned fish]]
Bony fishes ([[Biology:Actinopterygii|Actinopterygii]] and [[Biology:Sarcopterygii|Sarcopterygii]]) form a [[Biology:Taxonomy|taxonomic]] group called Osteichthyes (or [[Biology:Euteleostomi|Euteleostomi]], which includes also [[Biology:Tetrapod|land vertebrates]]); they have skeletons made of bone mostly, and can be contrasted with cartilaginous fishes (see below), which have skeletons made mainly of [[Biology:Cartilage|cartilage]] (except for their teeth, fin spines, and denticles).

Bony fishes are divided into [[Biology:Ray-finned fish|ray-finned]] and [[Biology:Lobe-finned fish|lobe-finned fish]]. Most living fish are ray-finned, an extremely diverse and abundant group consisting of over 30,000 [[Biology:Species|species]]. It is the largest class of vertebrates in existence today, making up more than 50% of species.<ref name="Nelson"/> In the distant past, lobe-finned fish were abundant; however, there are currently only 8 species. 

Bony fish have fin spines called lepidotrichia or "rays" (due to how the spines spread open). They typically have [[Biology:Swim bladder|swim bladder]]s, which allow the fish to alter the [[Physics:Relative density|relative density]] of its body and thus the [[Physics:Buoyancy|buoyancy]], so it can sink or float without having to use the fins to swim up and down. However, swim bladders are absent in many fish, most notably in lungfishes, who have evolved their swim bladders into primitive [[Medicine:Lung|lung]]s like their terrestrial relatives, the [[Biology:Tetrapod|tetrapod]]s. Bony fishes also have a pair of [[Biology:Operculum (fish)|operculum]] that draw water across the [[Biology:Gill|gill]]s, which help them breathe without needing to swim forward to force the water into the mouth across the gills.

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===Lobe-fins===
{{Main|Biology:Sarcopterygii}}
[[File:Latimeria Chalumnae - Coelacanth - NHMW.jpg|300px|thumb|right| Lobe-finned fishes, like this coelacanth, have fins that are borne on a fleshy, lobe-like, scaly stalk extending from the body. Due to the high number of fins it possesses, the coelacanth has high maneuverability and can orient its body in almost any direction in the water.]]
[[File:Pectoral fin Latimeria chalumnae.jpg|300px|thumb|right|Pectoral fin with fleshy lobe of ''Latimeria chalumnae'' (Citron / CC-BY-SA-3.0)]]
[[File:Pectoral fin coelacanth.jpg|300px|thumb|right|Skeleton of the pectoral girdle and fin of the extant coelacanth ''Latimeria chalumnae'' (Citron / CC-BY-SA-3.0)]]

[[Biology:Lobe-finned fish|Lobe-finned fish]]es form a class of bony fishes called Sarcopterygii. They have fleshy, [[Biology:Lobe (anatomy)|lobed]], paired fins, which are joined to the body by a series of bones.<ref>Clack, J. A. (2002) ''Gaining Ground''. Indiana University</ref> The fins of lobe-finned fish differ from those of all other fish in that each is borne on a fleshy, lobe-like, scaly stalk extending from the body. Pectoral and [[Biology:Pelvic fin|pelvic fin]]s have articulations resembling those of tetrapod limbs. These fins [[Biology:Evolution of tetrapods|evolved into legs]] of the first [[Biology:Tetrapod|tetrapod]] land vertebrates ([[Biology:Amphibian|amphibian]]s) in the [[Earth:Devonian|Devonian]] Period. Sarcopterygians also possess two dorsal fins with separate bases, as opposed to the single dorsal fin of most [[Biology:Ray-finned fish|ray-finned fish]] (except some teleosts). The caudal fin is either heterocercal (only fossil taxa) or diphycercal.

The [[Biology:Coelacanth|coelacanth]] is one type of living lobe-finned fish. Both extant members of this group, the [[Biology:West Indian Ocean coelacanth|West Indian Ocean coelacanth]] (''Latimeria chalumnae'') and the [[Biology:Indonesian coelacanth|Indonesian coelacanth]] (''Latimeria menadoensis''), are found in the genus ''[[Biology:Latimeria|Latimeria]].'' Coelacanths are thought to have evolved roughly into their current form about 408&nbsp;million years ago, during the early Devonian.{{r|Johanson2006}}

Locomotion of the coelacanths is unique to their kind. To move around, coelacanths most commonly take advantage of up or downwellings of the current and drift. They use their paired fins to stabilize their movement through the water. While on the ocean floor their paired fins are not used for any kind of movement. Coelacanths can create thrust for quick starts by using their caudal fins. Due to the high number of fins they possess, coelacanths have high maneuverability and can orient their bodies in almost any direction in the water. They have been seen doing headstands and swimming belly up. It is thought that their rostral organ helps give the coelacanth electroperception, which aids in their movement around obstacles.{{r|Fricke1987}}

[[Biology:Lungfish|Lungfish]] are also living lobe-finned fish. They occur in Africa (''[[Biology:Protopterus|Protopterus]]''), Australia (''[[Biology:Neoceratodus|Neoceratodus]]''), and South America (''[[Biology:Lepidosiren|Lepidosiren]]''). Lungfish evolved during the Devonian Period. Genetic studies and paleontological data confirm that lungfish are the closest living relatives of [[Biology:Tetrapod|land vertebrates]].<ref>{{cite journal |author1=Takezaki, N. |author2=Nishihara, H. |year=2017 |title=Support for lungfish as the closest relative of tetrapods by using slowly evolving ray-finned fish as the outgroup |journal=Genome Biology and Evolution |volume=9 |issue=1 |pages=93–101 |doi=10.1093/gbe/evw288 |pmid=28082606 |pmc=5381532}}</ref>

Fin arrangement and body shape is relatively conservative in lobe-finned fishes. However, there are a few examples from the fossil record that show aberrant [[Biology:Morphology|morphologies]], such as ''[[Biology:Allenypterus|Allenypterus]]'', ''[[Biology:Rebellatrix|Rebellatrix]]'', ''[[Biology:Foreyia|Foreyia]]'' or the tetrapodomorphs.

====Diversity of fins in lobe-finned fishes====
{{gallery
| height=100px
| mode=nolines
| noborder=true
|File:Tiktaalik restoration (side view) by ObsidianSoul 02 flipped.png|{{extinct}}''Tiktaalik roseae''
|File:Protopterus dolloi Boulenger.jpg|Spotted lungfish ''Protopterus dolloi''
|File:Barramunda.jpg|Queensland lungfish ''Neoceratodus forsteri''
|File:Dipterus valenciennesi1.jpg|{{extinct}}''[[Biology:Dipterus|Dipterus  valenciennesi]]''
|File:Osteolepis macrolepidotus Guide to the Gallery of Fishes.jpg|{{extinct}}''[[Biology:Osteolepis|Osteolepis macrolepidotus]]''
|File:Eusthenopteron foordi Guide to the Gallery of Fishes.jpg|{{extinct}}''[[Biology:Eusthenopteron|Eusthenopteron foordi]]''
|File:Holophagus gulo 1908 restoration.jpg|{{extinct}}''[[Biology:Undina (fish)|Undina gulo]]''
|File:Allenypterus montanus (Restoration) (cropped).jpg|{{extinct}}''[[Biology:Allenypterus|Allenypterus montanus]]''
|File:Coelacanth-bgiu.png|West Indian Ocean coelacanth ''Latimeria chalumnae''
|File:MawsoniaDB16 (cropped).jpg|{{extinct}}''[[Biology:Mawsonia gigas|Mawsonia gigas]]''
}}

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===Ray-fins===
{{further|Biology:Actinopterygii}}
[[File:Haddock fins.tiff|thumb|300px|right|The [[Biology:Haddock|haddock]], a type of cod, is ray-finned. It has three dorsal and two anal fins]]

[[Biology:Ray-finned fish|Ray-finned fish]]es form a class of bony fishes called Actinopterygii. Their fins contain spines or rays. A fin may contain only spiny rays, only soft rays, or a combination of both. If both are present, the spiny rays are always [[Biology:Anatomical terms of location#Anterior and posterior|anterior]]. Spines are generally stiff and sharp. Rays are generally soft, flexible, segmented, and may be branched. This segmentation of rays is the main difference that separates them from spines; spines may be flexible in certain species, but they will never be segmented.

Spines have a variety of uses. In [[Biology:Catfish|catfish]], they are used as a form of defense; many catfish have the ability to lock their spines outwards. [[Biology:Triggerfish|Triggerfish]] also use spines to lock themselves in crevices to prevent them being pulled out.

Lepidotrichia are usually composed of [[Biology:Bone|bone]], but those of early [[Biology:Osteichthyes|osteichthyans]] - such as ''[[Biology:Cheirolepis|Cheirolepis]]'' - also had dentine and [[Biology:Tooth enamel|enamel]].<ref name="Zylberberg2016">{{cite journal|last1=Zylberberg|first1=L.|last2=Meunier|first2=F. J.|last3=Laurin|first3=M.|title=A microanatomical and histological study of the postcranial dermal skeleton of the Devonian actinopterygian ''Cheirolepis canadensis''|journal=Acta Palaeontologica Polonica|date=2016|volume=61 |issue= 2|pages=363–376|doi=10.4202/app.00161.2015|doi-access=free}}</ref> They are segmented and appear as a series of disks stacked one on top of another. They may have been derived from dermal scales.<ref name="Zylberberg2016" /> The genetic basis for the formation of the fin rays is thought to be genes coded for the production of certain proteins. It has been suggested that the evolution of the tetrapod limb from lobe-finned fishes is related to the loss of these proteins.<ref name="zhang2010">{{Cite journal | last1 = Zhang | first1 = J. | last2 = Wagh | first2 = P. | last3 = Guay | first3 = D. | last4 = Sanchez-Pulido | first4 = L. | last5 = Padhi | first5 = B. K. | last6 = Korzh | first6 = V. | last7 = Andrade-Navarro | first7 = M. A. | last8 = Akimenko | first8 = M. A.| title = Loss of fish actinotrichia proteins and the fin-to-limb transition | journal = Nature | volume = 466 | issue = 7303 | pages = 234–237 | year = 2010 | pmid = 20574421 | doi = 10.1038/nature09137|bibcode = 2010Natur.466..234Z | s2cid = 205221027 }}</ref>

{{clear}}

====Diversity of fins in ray-finned fishes====
{{gallery
| height=100px
| mode=nolines
| noborder=true
|File:C jordani.JPG|Fanfin angler ''[[Biology:Caulophryne jordani|Caulophryne jordani]]''
|File:Halieutichthys aculeatus 2.jpg|Pancake batfish ''Halieutichthys aculeatus''
|File:Ranzania laevis (Slender sunfish).gif| Slender sunfish ''Ranzania laevis''
|File:Pteraclis carolinus.jpg|[[Biology:Pteraclis|Fanfish]] ''Pteraclis carolinus''
|File:Sternoptyx diaphana.jpg|Diaphanous hatchetfish ''[[Biology:Sternoptyx diaphana|Sternoptyx diaphana]]''
|File:Hoplostethus mediterraneus mediterraneus.jpg|Silver roughy ''Hoplostethus mediterraneus''
|File:Lophonectes gallus (Crested flounder).gif|[[Biology:Crested flounder|Crested flounder]] ''Lophonectes gallus''
|File:Equetuslanceolatus.jpg|[[Biology:Jack-knifefish|Jack-knifefish]] ''Equetus lanceolatus''
|File:Brama brama.jpg|Atlantic pomfret ''Brama brama''
|File:Polyprion americanus.jpg|Atlantic wreckfish ''Polyprion americanus''
|File:Tetrodon stellatus Achilles 183.jpg|Stellate pufferfish ''[[Biology:Arothron stellatus|Arothron stellatus]]''
|File:Ceratias uranoscopus.jpg|Stargazing seadevil ''[[Biology:Ceratias uranoscopus|Ceratias uranoscopus]]''
|File:Poromitra unicornis.jpg|[[Biology:Ridgehead|Ridgehead]] ''Poromitra unicornis''
|File:Exocoetus evolans Mintern 120.jpg|Tropical two-wing flyingfish ''Exocoetus evolans''
|File:Benthocometes robustus.jpg|[[Biology:Cusk-eel|Cusk-eel]] ''Benthocometes robustus''
|File:Trachonurus sulcatus.jpg|Rattail ''Trachonurus sulcatus''
|File:Bathypterois grallator.jpg|Tripod fish ''[[Biology:Bathypterois grallator|Bathypterois grallator]]''
|File:King of herrings.png|[[Biology:Giant oarfish|Giant oarfish]] ''Regalecus glesne''
|File:Tetrapturus angustirostris (Shortbill spearfish).gif|[[Biology:Shortbill spearfish|Shortbill spearfish]] ''Tetrapturus angustirostris''
|File:Sternarchorhynchus oxyrhynchus.jpg|[[Biology:Ghost knifefish|Ghost knifefish]] ''Sternarchorhynchus oxyrhynchus''
|File:Remora brachyptera (Spearfish remora).gif|[[Biology:Remora|Remora]] ''Remora brachyptera''
|File:Salarias periophthalmus Ford 69.jpg|Blue-dashed rockskipper ''Blenniella periophthalmus''
|File:Nile bichir.png|Nile bichir ''Polypterus bichir''
|File:Oncorhynchus clarkii clarkii.jpg|[[Biology:Coastal cutthroat trout|Coastal cutthroat trout]] ''Oncorhynchus clarkii''
|File:Schilbe mystus.jpg|[[Biology:African butter catfish|African butter catfish]] ''Schilbe mystus''
|File:Conger eel.jpg|Conger eel ''Leptocephalus conger''
}}

==Cartilaginous fishes==
[[File:Parts of a shark.svg|thumb|400px|right| 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.]]
[[File:Carcharhinus amblyrhynchos JNC1111 Tail.JPG|thumb|left|Caudal fin of a [[Biology:Grey reef shark|grey reef shark]]]]

Cartilaginous fishes form a class of fishes called Chondrichthyes. They have skeletons made of [[Biology:Cartilage|cartilage]] rather than [[Biology:Bone|bone]]. The class includes [[Biology:Shark|shark]]s, [[Biology:Batoidea|ray]]s and [[Biology:Chimaera|chimaera]]s.

Shark fin skeletons are elongated and supported with soft and unsegmented rays named ceratotrichia, filaments of elastic protein resembling the horny [[Biology:Keratin|keratin]] in hair and feathers.{{sfn|Hamlett|1999|p=528}} Originally the pectoral and pelvic girdles, which do not contain any dermal elements, did not connect. In later forms, each pair of fins became ventrally connected in the middle when scapulocoracoid and puboischiadic bars evolved. In [[Biology:Batoidea|rays]], the pectoral fins have connected to the head and are very flexible. One of the primary characteristics present in most sharks is the heterocercal tail, which aids in locomotion.<ref>[http://jeb.biologists.org/cgi/reprint/205/16/2365.pdf Function of the heterocercal tail in sharks: quantitative wake dynamics during steady horizontal swimming and vertical maneuvering] - The Journal of Experimental Biology 205, 2365–2374 (2002)</ref> Most sharks have eight fins. Sharks can only drift away from objects directly in front of them because their fins do not allow them to move in the tail-first direction.<ref name=langoni>{{cite web|archive-url=https://web.archive.org/web/20100805003021/http://langonigraphix.com/skeleton.html|archive-date=August 5, 2010
|url=http://langonigraphix.com/skeleton.html
|title=A Shark's Skeleton & Organs
|access-date=August 14, 2009
}}</ref>

Unlike modern cartilaginous fish, members of stem chondrichthyan lineages (e.g. the {{extinct}}[[Biology:Climatiiformes|climatiids]] and the {{extinct}}[[Biology:Diplacanthiformes|diplacanthids]])<ref>{{Cite book |last=Burrow |first=Carole |url=http://worldcat.org/oclc/1335983356 |title=Acanthodii, Stem Chondrichthyes |year=2021 |publisher=Verlag Dr. Friedrich Pfeil |isbn=978-3-89937-271-7 |oclc=1335983356}}</ref> possessed pectoral dermal plates as well as dermal spines associated with the paired fins. The oldest species demonstrating these features is the {{extinct}}acanthodian {{extinct}}''Fanjingshania renovata''<ref>{{Cite journal |last1=Andreev |first1=Plamen S. |last2=Sansom |first2=Ivan J. |last3=Li |first3=Qiang |last4=Zhao |first4=Wenjin |last5=Wang |first5=Jianhua |last6=Wang |first6=Chun-Chieh |last7=Peng |first7=Lijian |last8=Jia |first8=Liantao |last9=Qiao |first9=Tuo |last10=Zhu |first10=Min |date=September 2022 |title=Spiny chondrichthyan from the lower Silurian of South China |url=https://www.nature.com/articles/s41586-022-05233-8 |journal=Nature |language=en |volume=609 |issue=7929 |pages=969–974 |doi=10.1038/s41586-022-05233-8 |pmid=36171377 |bibcode=2022Natur.609..969A |s2cid=252570103 |issn=1476-4687}}</ref> from the lower [[Earth:Silurian|Silurian]] ([[Earth:Aeronian|Aeronian]]) of China. Fanjingshania possess compound pectoral plates composed of dermal scales fused to a bony plate and fin spines formed entirely of bone. Fin spines associated with the dorsal fins are rare among extant cartilaginous fishes, but are present, for instance, in ''[[Biology:Heterodontus|Heterodontus]]'' or ''Squalus''. Dorsal fin spines are typically developed in many fossil groups, such as in {{extinct}}[[Biology:Hybodontiformes|Hybodontiformes]], {{extinct}}Ctenacanthiformes or {{extinct}}[[Biology:Xenacanthida|Xenacanthida]]. In {{extinct}}''[[Biology:Stethacanthus|Stethacanthus]]'', the first dorsal fin spine was modified, forming a spine-brush complex.

As with most fish, the tails of sharks provide thrust, making speed and acceleration dependent on tail shape. Caudal fin shapes vary considerably between shark species, due to their evolution in separate environments. Sharks possess a heterocercal caudal fin in which the dorsal portion is usually noticeably larger than the ventral portion. This is because the shark's [[Biology:Vertebral column|vertebral column]] extends into that dorsal portion, providing a greater surface area for [[Biology:Muscle|muscle]] attachment. This allows more efficient [[Biology:Animal locomotion|locomotion]] among these negatively [[Physics:Buoyancy|buoyant]] cartilaginous fish. By contrast, most bony fish possess a homocercal caudal fin.<ref>{{cite web|url=http://www.fathom.com/course/21701777/session1.html|title=Jaws: The Natural History of Sharks|last=Michael|first=Bright|publisher=Columbia University|access-date=2009-08-29|url-status=dead|archive-url=https://web.archive.org/web/20111224122118/http://www.fathom.com/course/21701777/session1.html|archive-date=2011-12-24}}</ref>

[[Biology:Tiger shark|Tiger shark]]s have a large upper [[Biology:Lobe (anatomy)|lobe]], which allows for slow cruising and sudden bursts of speed. The tiger shark must be able to twist and turn in the water easily when hunting to support its varied diet, whereas the [[Biology:Porbeagle|porbeagle shark]], which hunts schooling fish such as [[Biology:Mackerel|mackerel]] and [[Biology:Herring|herring]], has a large lower lobe to help it keep pace with its fast-swimming prey.<ref name="Nelson">{{cite book
| last=Nelson
| first=Joseph S.
| title= Fishes of the World
| publisher=John Wiley and Sons
|location=New York
| year= 1994
|isbn= 978-0-471-54713-6
| oclc=28965588| title-link=Fishes of the World
}}</ref> Other tail adaptations help sharks catch prey more directly, such as the [[Biology:Thresher shark|thresher shark]]'s usage of its powerful, elongated upper lobe to stun fish and squid.

On the other hand, rays rely on their enlarged pectoral fins for propulsion. Similarly enlarged pectoral fins can be found in the extinct {{extinct}}[[Biology:Petalodontiformes|Petalodontiformes]] (e.g. {{extinct}}''[[Biology:Belantsea|Belantsea]]'', {{extinct}}''[[Biology:Janassa|Janassa]]'', {{extinct}}''[[Biology:Menaspis|Menaspis]]''), which belong to [[Biology:Holocephali|Holocephali]] (ratfish and their fossil relatives), or in {{extinct}}''[[Biology:Aquilolamna|Aquilolamna]]'' (Selachimorpha) and {{extinct}}''[[Biology:Squatinactis|Squatinactis]]'' (Squatinactiformes). Some cartilaginous fishes have an eel-like locomotion (e.g. ''[[Biology:Chlamydoselachus|Chlamydoselachus]]'', {{extinct}}''Thrinacoselache'',<ref>{{cite journal|last1=Grogan|first1=Eileen D.|last2=Lund|first2=Richard|title=A basal elasmobranch, ''Thrinacoselache gracia'' n. gen and sp., (Thrinacodontidae, new family) from the Bear Gulch Limestone, Serpukhovian of Montana, USA |journal=Journal of Vertebrate Paleontology| date=2008 |volume=28 |issue=4 |pages=970–988 |doi=10.1671/0272-4634-28.4.970|bibcode=2008JVPal..28..970G |s2cid=84735866 }}</ref> {{extinct}}''Phoebodus''<ref>{{cite journal|last1=Frey |first1=Linda |last2=Coates |first2=Michael |last3=Ginter |first3=Michał |last4=Hairapetian |first4=Vachik |last5=Rücklin |first5=Martin |last6=Jerjen |first6=Iwan |last7=Klug |first7=Christian |title=The early elasmobranch ''Phoebodus'': phylogenetic relationships, ecomorphology and a new time-scale for shark evolution |journal=Proceedings of the Royal Society B: Biological Sciences |date=2019 |volume=286 |issue=1912 |doi=10.1098/rspb.2019.1336|pmid=31575362 |pmc=6790773 |s2cid=203619135 }}</ref>)

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===Diversity of fins in cartilaginous fishes===
{{gallery
| height=100px
| mode=nolines
| noborder=true
|File:Scyliorhinus canicula1.jpg|Small-spotted catshark ''Scyliorhinus canicula''
|File:White shark (Duane Raver).png| Great white shark ''Carcharodon carcharias''
|File:Alopias vulpinus.jpg|Common thresher ''Alopias vulpinus''
|File:Pristis perrotteti Day Achilles 191.jpg|Largetooth sawfish ''Pristis perotteti''
|File:Torpedo marmorata by risso.png|Marbled electric ray ''Torpedo marmorata''
|File:Dasyatis bennettii by jordan and richardson.png|Bennett's stingray ''Hemitrygon bennettii''
|File:Chlamydoselachus anguineus1.jpg|Frilled shark ''Chlamydoselachus anguineus''
|File:LebachacanthusDB18.jpg|The {{extinct}}[[Biology:Xenacanthida|xenacanth]] {{extinct}}''[[Biology:Lebachacanthus|Lebachacanthus senckenbergianus]]''
|File:Stethacanthus1DB.jpg|The {{extinct}}[[Biology:Symmoriiformes|symmoriiform]] {{extinct}}''Stethacanthus productus''
|File:Wodnika striatula.jpg|The {{extinct}}ctenacanthid {{extinct}}''Wodnika striatula''
|File:Bandringa SW.png|The elasmobranch {{extinct}}''[[Biology:Bandringa|Bandringa rayi]]''
|File:Iniopterygian.jpg| The {{extinct}}[[Biology:Iniopterygiformes|Iniopterygiformes]] {{extinct}}''Sibyrhynchus denisoni'' (Holocephali)
|File:Chimaera cubana.JPG|Cuban chimaera ''Chimaera cubana''
|File:Callorhinchus callorhynchus.JPG|American elephantfish ''Callorhinchus callorhynchus''
}}

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===Shark finning===
[[File:Shark finning icon.jpg|thumb|100 px|Shark fin]]
According to the Humane Society International, approximately 100 million sharks are killed each year for their fins, in an act known as shark finning.<ref>[http://www.hsi.org/issues/shark_finning/ Shark Finning]. Humane Society International.</ref> After the fins are cut off, the mutilated sharks are thrown back in the water and left to die.

In some countries of [[Earth:Asia|Asia]], shark fins are a culinary delicacy, such as shark fin soup.<ref>{{cite journal | author = Vannuccini S | year = 1999 | title = Shark utilization, marketing and trade | journal = FAO Fisheries Technical Paper | volume = 389 | url = http://www.fao.org/DOCREP/005/X3690E/x3690e0p.htm }}</ref> Currently, international concerns over the sustainability and welfare of sharks have impacted consumption and availability of shark fin soup worldwide.<ref>{{Cite web|url=https://www.washingtonpost.com/world/in-china-victory-for-wildlife-conservation-as-citizens-persuaded-to-give-up-shark-fin-soup/2013/10/19/e8181326-3646-11e3-89db-8002ba99b894_print.html|title=In China, victory for wildlife conservation as citizens persuaded to give up shark fin soup - The Washington Post|website=www.washingtonpost.com|access-date=20 January 2017}}</ref> Shark finning is prohibited in many countries.

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==Fin functions==
===Generating thrust===
[[Physics:Foil (fluid mechanics)|Foil]] shaped [[Biology:Fin|fin]]s generate [[Thrust|thrust]] when moved, the lift of the fin sets water or air in motion and pushes the fin in the opposite direction. Aquatic animals get significant [[Thrust|thrust]] by moving fins back and forth in water. Often the tail fin is used, but some aquatic animals generate thrust from pectoral fins.<ref name=Sfakiotakis />

{{multiple image
| align             = left
| direction         = horizontal
| header            = Moving fins can provide thrust
| header_align      = center
| header_background = 
| image1            = Barb gonio 080525 9610 ltn Cf.jpg
| width1            = 122
| alt1              = 
| caption1          = Fish get thrust moving vertical tail fins from side to side.
| image3            = Dasyatis thetidis.jpg
| width3            = 135
| alt3              = 
| caption3          = Stingrays get thrust from large pectoral fins.
}}

{{multiple image
| align             = right
| direction         = vertical
| width             = 150
| header            = 
| header_align      = center
| header_background = 
| image2            = Thunnus obesus (Bigeye tuna) diagram cropped.GIF
| alt2              = 
| caption2          = {{center|1=Drawing by Dr Tony Ayling
----
Finlets may influence the way a [[Vortex|vortex]] develops around the tail fin.}}
}}

[[Physics:Cavitation|Cavitation]] occurs when negative pressure causes bubbles (cavities) to form in a liquid, which then promptly and violently collapse. It can cause significant damage and wear.<ref name=Franc>Franc, Jean-Pierre and Michel, Jean-Marie (2004) [https://books.google.com/books?id=QJOQYa_oo24C&q=Cavitation ''Fundamentals of Cavitation''] Springer. {{ISBN|9781402022326}}.</ref> Cavitation damage can occur to the tail fins of powerful swimming marine animals, such as dolphins and tuna. Cavitation is more likely to occur near the surface of the ocean, where the ambient water pressure is relatively low. Even if they have the power to swim faster, dolphins may have to restrict their speed because collapsing cavitation bubbles on their tail are too painful.<ref name=hurts>{{cite news | last = Brahic | first = Catherine | title = Dolphins swim so fast it hurts   | publisher = New Scientist | date = 2008-03-28 | url = https://www.newscientist.com/channel/life/dn13553-dolphins-swim-so-fast-it-hurts.html | access-date = 2008-03-31}}</ref> Cavitation also slows tuna, but for a different reason. Unlike dolphins, these fish do not feel the bubbles, because they have bony fins without nerve endings. Nevertheless, they cannot swim faster because the cavitation bubbles create a vapor film around their fins that limits their speed. Lesions have been found on tuna that are consistent with cavitation damage.<ref name=hurts/>

Scombrid fishes (tuna, mackerel and bonito) are particularly high-performance swimmers. Along the margin at the rear of their bodies is a line of small rayless, non-retractable fins, known as finlets. There has been much speculation about the function  of these finlets. Research done in 2000 and 2001 by Nauen and Lauder indicated that "the finlets have a hydrodynamic effect on local flow during steady swimming" and that "the most posterior finlet is oriented to redirect flow into the developing tail vortex, which may increase thrust produced by the tail of swimming mackerel".<ref>{{cite journal | last1 = Nauen | first1 = JC | last2 = Lauder | first2 = GV | year = 2001a | title = Locomotion in scombrid fishes: visualization of flow around the caudal peduncle and finlets of the Chub mackerel ''Scomber japonicus'' | url = http://jeb.biologists.org/content/204/13/2251.long | journal = Journal of Experimental Biology | volume = 204 | issue = Pt 13| pages = 2251–63 | doi = 10.1242/jeb.204.13.2251 | pmid = 11507109 }}</ref><ref>{{cite journal | last1 = Nauen | first1 = JC | last2 = Lauder | first2 = GV | s2cid = 28910289 | year = 2001b | title = Three-dimensional analysis of finlet kinematics in the Chub mackerel ''(Scomber japonicus)'' | journal = The Biological Bulletin | volume = 200 | issue = 1| pages = 9–19 | doi=10.2307/1543081| pmid = 11249216 | jstor = 1543081 | url = https://www.biodiversitylibrary.org/part/10992 }}</ref><ref>{{cite journal | last1 = Nauen | first1 = JC | last2 = Lauder | first2 = GV | year = 2000 | title = Locomotion in scombrid fishes: morphology and kinematics of the finlets of the Chub mackerel ''Scomber japonicus'' | url = http://jeb.biologists.org/content/203/15/2247.full.pdf | journal = Journal of Experimental Biology | volume = 203 | issue = Pt 15| pages = 2247–59 | doi = 10.1242/jeb.203.15.2247 | pmid = 10887065 }}</ref>

Fish use multiple fins, so it is possible that a given fin can have a hydrodynamic interaction with another fin. In particular, the fins immediately upstream of the caudal (tail) fin may be proximate fins that can directly affect the flow dynamics at the caudal fin. In 2011, researchers using [[Particle image velocimetry|volumetric imaging]] techniques were able to generate "the first instantaneous three-dimensional views of wake structures as they are produced by freely swimming fishes". They found that "continuous tail beats resulted in the formation of a linked chain of vortex rings" and that "the dorsal and anal fin wakes are rapidly entrained by the caudal fin wake, approximately within the timeframe of a subsequent tail beat".<ref>{{cite journal | last1 = Flammang | first1 = BE | last2 = Lauder | first2 = GV | last3 = Troolin | first3 = DR | last4 = Strand | first4 = TE | year = 2011 | title = Volumetric imaging of fish locomotion | url = http://intl-rsbl.royalsocietypublishing.org/content/7/5/695.full | journal = Biology Letters | volume = 7 | issue = 5| pages = 695–698 | doi = 10.1098/rsbl.2011.0282 | pmid = 21508026 | pmc = 3169073 }}</ref>

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===Controlling motion===
Once motion has been established, the motion itself can be controlled with the use of other fins.<ref name=Sfakiotakis /><ref>{{cite journal | last1 = Fish | first1 = FE | last2 = Lauder | first2 = GV | s2cid = 4983205 | year = 2006 | title = Passive and active flow control by swimming fishes and mammals | journal = Annual Review of Fluid Mechanics | volume = 38 | issue =1 | pages = 193–224 | doi = 10.1146/annurev.fluid.38.050304.092201 | bibcode = 2006AnRFM..38..193F }}</ref>

{{multiple image
| align             = left
| direction         = horizontal
| header            = Specialised fins are used to control motion
| header_align      = center
| header_background = 
| image1            = Rotations.png
| width1            = 237
| alt1              = 
| caption1          = Like boats and airplanes, fish need some control over six [[Physics:Degrees of freedom (mechanics)|degrees of freedom]], three translational (heaving, swaying and surging) and three rotational (pitching, yawing and rolling).<ref name=Magnuson>Magnuson JJ (1978) [https://books.google.com/books?id=wnjnyAafAzUC&pg=PA239 "Locomotion by scombrid fishes: Hydromechanics, morphology and behavior"] in ''Fish Physiology'', Volume 7: Locomotion, WS Hoar and DJ Randall (Eds) Academic Press. Page 240–308. {{ISBN|9780123504074}}.</ref><ref>[http://www.pomorci.com/Zanimljivosti/Ship's%20movements%20at%20sea.pdf Ship's movements at sea]  {{webarchive|url=https://web.archive.org/web/20111125015923/http://www.pomorci.com/Zanimljivosti/Ship%27s%20movements%20at%20sea.pdf |date=November 25, 2011 }} Retrieved 22 November 2012.</ref><ref>Rana and Joag (2001) [https://books.google.com/books?id=1kxkdWGa9-cC&dq=yaw+roll+pitch+airplane&pg=PA391 ''Classical Mechanics''] Page 391, Tata McGraw-Hill Education. {{ISBN|9780074603154}}.</ref>
| image2            = Holacanthus ciliaris 1.jpg
| width2            = 215
| alt2              = 
| caption2          = Many reef fish have pectoral and pelvic fins optimised for flattened bodies.<ref name=Alevizon />
| image3            = White shark (cropped).jpg
| width3            = 228
| alt3              = 
| caption3          = The dorsal fin of a white shark contain dermal fibers that work "like riggings that stabilize a ship's mast", and stiffen dynamically as the shark swims faster to control roll and yaw.<ref>{{Cite journal | last1 = Lingham-Soliar | first1 = T. | s2cid = 827610 | title = Dorsal fin in the white shark,Carcharodon carcharias: A dynamic stabilizer for fast swimming | doi = 10.1002/jmor.10207 | journal = Journal of Morphology | volume = 263 | issue = 1 | pages = 1–11 | year = 2005 | pmid =  15536651}}</ref>
}}

{{clear}}

The bodies of reef fishes are often shaped differently from [[Biology:Pelagic fish|open water fishes]]. Open water fishes are usually built for speed, streamlined like torpedoes to minimise friction as they move through the water. Reef fish operate in the relatively confined spaces and complex underwater landscapes of [[Earth:Coral reef|coral reef]]s. For this manoeuvrability is more important than straight line speed, so coral reef fish have developed bodies which optimize their ability to dart and change direction. They outwit predators by dodging into fissures in the reef or playing hide and seek around coral heads.<ref name=Alevizon>Alevizon WS (1994) [https://www.amazon.com/dp/1559920777 "Pisces Guide to Caribbean Reef Ecology"]  Gulf Publishing Company {{ISBN|1-55992-077-7}}</ref> The pectoral and pelvic fins of many reef fish, such as [[Biology:Butterflyfish|butterflyfish]], [[Biology:Damselfish|damselfish]] and [[Biology:Pomacanthidae|angelfish]], have evolved so they can act as brakes and allow complex manoeuvres.<ref name=FMNH>[http://www.flmnh.ufl.edu/fish/education/HowSwim/HowSwim.html Ichthyology] ''Florida Museum of Natural History''. Retrieved 22 November 2012.</ref> Many reef fish, such as [[Biology:Butterflyfish|butterflyfish]], [[Biology:Damselfish|damselfish]] and [[Biology:Pomacanthidae|angelfish]], have evolved bodies which are deep and laterally compressed like a pancake, and will fit into fissures in rocks. Their pelvic and pectoral fins have evolved differently, so they act together with the flattened body to optimise manoeuvrability.<ref name=Alevizon /> Some fishes, such as puffer fish, [[Biology:Filefish|filefish]] and trunkfish, rely on pectoral fins for swimming and hardly use tail fins at all.<ref name=FMNH />

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===Reproduction===
{{multiple image
| align             = right
| direction         = vertical
| width             = 220
| image1            = Gambusia affinis male.jpg
| alt1              = 
| caption1          = This male [[Biology:Mosquitofish|mosquitofish]] has a gonopodium, an anal fin which functions as an intromittent organ.<ref>{{cite web|last=Masterson|first=J|title=''Gambusia affinis''|url=http://www.sms.si.edu/irlspec/Gambusia_affinis.htm|publisher=Smithsonian Institution|access-date=21 October 2011}}</ref><ref>{{cite journal|last=Kuntz|first=Albert|title=Notes on the Habits, Morphology of the Reproductive Organs, and Embryology of the Viviparous Fish Gambusia affinis|url=https://books.google.com/books?id=E8QWAAAAYAAJ&pg=PA178-IA7|volume=33|year=1913|pages=181–190|journal=Bulletin of the United States Bureau of Fisheries}}</ref>
| image2            = Carcharhinus brevipinna JNC3077 Male parts.JPG
| alt2              = 
| caption2          = This young male [[Biology:Spinner shark|spinner shark]] has claspers, a modification to the pelvic fins which also function as intromittent organs.
}}

Male cartilaginous fishes (sharks and rays), as well as the males of some live-bearing ray finned fishes, have fins that have been modified to function as [[Biology:Intromittent organ|intromittent organ]]s, reproductive appendages which allow internal fertilization. In ray finned fish they are called ''gonopodia'' or ''andropodia'', and in cartilaginous fish they are called ''claspers''.

''Gonopodia'' are found on the males of some species in the [[Biology:Anablepidae|Anablepidae]] and [[Biology:Poeciliidae|Poeciliidae]] families. They are anal fins that have been modified to function as movable intromittent organs and are used to impregnate females with milt during mating.  The third, fourth and fifth rays of the male's anal fin are formed into a tube-like structure in which the sperm of the fish is ejected.<ref>Kapoor BG and Khanna B (2004) [https://books.google.com/books?id=I7WhoPBdAooC&dq=andropodium+Gonopodium&pg=PA498 ''Ichthyology Handbook''] pp. 497–498, Springer Science & Business Media. {{ISBN|9783540428541}}.</ref> When ready for mating, the gonopodium becomes erect and points forward towards the female. The male shortly inserts the organ into the sex opening of the female, with hook-like adaptations that allow the fish to grip onto the female to ensure impregnation. If a female remains stationary and her partner contacts her vent with his gonopodium, she is fertilized. The sperm is preserved in the female's oviduct. This allows females to fertilize themselves at any time without further assistance from males. In some species, the gonopodium may be half the total body length. Occasionally the fin is too long to be used, as in the "lyretail" breeds of ''Xiphophorus helleri''. Hormone treated females may develop gonopodia. These are useless for breeding.

Similar organs with similar characteristics are found in other fishes, for example the ''andropodium'' in the ''[[Biology:Hemirhamphodon|Hemirhamphodon]]'' or in the [[Biology:Goodeidae|Goodeidae]]<ref>Helfman G, Collette BB, Facey DH and Bowen BW (2009) [http://www.blackwellpublishing.com/helfman/ ''The Diversity of Fishes: Biology, Evolution, and Ecology''] p. 35, Wiley-Blackwell. {{ISBN|978-1-4051-2494-2}}</ref> or the ''gonopodium'' in the [[Earth:Middle Triassic|Middle Triassic]] {{extinct}}''[[Biology:Saurichthys|Saurichthys]]'', the oldest known example of viviparity in a ray-finned fish.<ref>{{cite journal | author = Maxwell  | display-authors = etal | year = 2018 | title = Re‐evaluation of the ontogeny and reproductive biology of the Triassic fish ''Saurichthys'' (Actinopterygii, Saurichthyidae) | journal = Palaeontology | volume = 61 | pages = 559–574 | doi = 10.5061/dryad.vc8h5 }}</ref>

''[[Biology:Clasper|Clasper]]s'' are found on the males of cartilaginous fishes. They are the posterior part of the pelvic fins that have also been modified to function as intromittent organs, and are used to channel semen into the female's [[Biology:Cloaca|cloaca]] during copulation. The act of mating in sharks usually includes raising one of the claspers to allow water into a siphon through a specific [[Biology:Body orifice|orifice]].  The clasper is then inserted into the cloaca, where it opens like an umbrella to anchor its position. The siphon then begins to contract expelling water and sperm.<ref>{{cite web |url=http://www.fishbase.org/Glossary/Glossary.php?q=clasper&language=english&sc=is |title=System glossary |work=FishBase |access-date=2013-02-15}}</ref><ref>{{cite book |title=The Timetree of Life: Cartilaginous Fishes (Chondrichthyes) |last1=Heinicke |first1=Matthew P. |last2=Naylor |first2=Gavin J. P. |last3=Hedges |first3=S. Blair |year=2009 |publisher=Oxford University Press |isbn=978-0191560156 |page=320 |url=https://books.google.com/books?id=9rt1c1hl49MC&q=Manta+birostris+fossil&pg=PA320 }}</ref>

{{clear}}

===Other functions===
Other uses of fins include walking and perching on the sea floor, gliding over water, cooling of body temperature, stunning of prey, display (scaring of predators, courtship), defence (venomous fin spines, locking between corals), luring of prey, and attachment structures.

The [[Biology:Indo-Pacific sailfish|Indo-Pacific sailfish]] has a prominent dorsal fin. Like [[Biology:Scombridae|scombroid]]s and other [[Biology:Billfish|billfish]], they streamline themselves by retracting their dorsal fins into a groove in their body when they swim.<ref name=Cavendish /> The huge dorsal fin, or sail, of the sailfish is kept retracted most of the time. Sailfish raise them if they want to herd a school of small fish, and also after periods of high activity, presumably to cool down.<ref name=Cavendish>[https://books.google.com/books?id=va1ODFo_tdUC&dq=Billfish&pg=PA332 ''Aquatic Life of the World''] pp. 332–333, Marshall Cavendish Corporation, 2000. {{ISBN|9780761471707}}.</ref><ref>Dement J [http://www.littoralsociety.org/userfiles/doccenter/Species%20Spotlight%20Atlantic%20Sailfish.pdf Species Spotlight: Atlantic Sailfish (''Istiophorus albicans'')] {{webarchive |url=https://web.archive.org/web/20101217230458/http://www.littoralsociety.org/userfiles/doccenter/Species%20Spotlight%20Atlantic%20Sailfish.pdf |date=December 17, 2010 }} ''littoralsociety.org''. Retrieved 1 April 2012.</ref>

{{multiple image
| align             = left
| caption_align     = center
| direction         = horizontal
| header            = Other uses of fins
| header_align      = center
| header_background = 
| image1            = Commerson's frogfish (Antennarius commerson) in Waikiki Aquarium.JPG
| width1            = 178
| alt1              = 
| caption1          = [[Biology:Frogfish|Frogfish]] use their pectoral and pelvic fins to '''walk''' along the ocean bottom.<ref>{{cite book |author= Bertelsen E and Pietsch TW|year=1998|title=Encyclopedia of Fishes|publisher= Academic Press|location=San Diego|pages= 138–139|isbn= 978-0-12-547665-2}}</ref>
| image2            = Sailfin flyingfish.jpg
| width2            = 227
| alt2              = 
| caption2          = [[Biology:Flying fish|Flying fish]] achieve sufficient lift to '''glide''' above the surface of the water thanks to their enlarged pectoral fins.
| image3            = Istiophorus platypterus .jpg
| width3            = 218
| alt3              = 
| caption3          = Large retractable dorsal fin of the [[Biology:Indo-Pacific sailfish|Indo-Pacific sailfish]], possibly used for '''cooling''' ([[Physics:Thermoregulation|thermoregulation]]).
| image4            = Alopias vulpinus Gervais.jpg
| width4            = 296
| alt4              = 
| caption4          = The [[Biology:Thresher shark|thresher shark]] uses its very elongated caudal fin to '''stun''' prey.
| image5            = Tripod fish.jpg
| width5            = 209
| alt5              = 
| caption5          = Species of [[Biology:Ipnopidae|tripod fish]] ''[[Biology:Bathypterois|Bathypterois]]'' have elongated pectoral and pelvic fins, and an elongated caudal fin, which allow them to move and '''perch''' on the ocean floor.
}}

{{clear}}

The [[Biology:Oriental flying gurnard|oriental flying gurnard]] has large pectoral fins which it normally holds against its body, and expands when threatened to scare predators. Despite its name, it is a [[Biology:Demersal fish|demersal fish]], not a flying fish, and uses its pelvic fins to walk along the bottom of the ocean.<ref>[http://australianmuseum.net.au/Purple-Flying-Gurnard-Dactyloptena-orientalis/ Purple Flying Gurnard, ''Dactyloptena orientalis'' (Cuvier, 1829)] ''Australian Museum''. Updated: 15 September 2012. Retrieved: 2 November 2012.</ref><ref>{{FishBase| genus=Dactyloptena | species=orientalis | year=2012 | month=November }}</ref>

Fins can have an adaptive significance as sexual ornaments. During courtship, the female [[Biology:Cichlid|cichlid]], ''[[Biology:Pelvicachromis taeniatus|Pelvicachromis taeniatus]]'', displays a large and visually arresting purple [[Biology:Pelvic fin|pelvic fin]]. "The researchers found that males clearly preferred females with a larger pelvic fin and that pelvic fins grew in a more disproportionate way than other fins on female fish."<ref>[https://www.sciencedaily.com/releases/2010/10/101007210540.htm Female fish flaunt fins to attract a mate] ''ScienceDaily''. 8 October 2010.</ref><ref>{{cite journal | last1 = Baldauf | first1 = SA | last2 = Bakker | first2 = TCM | last3 = Herder | first3 = F | last4 = Kullmann | first4 = H | last5 = Thünken | first5 = T | year = 2010 | title = Male mate choice scales female ornament allometry in a cichlid fish | journal = BMC Evolutionary Biology | volume = 10 | page = 301 | doi = 10.1186/1471-2148-10-301 | pmid = 20932273 | pmc = 2958921 | bibcode = 2010BMCEE..10..301B | doi-access = free }}</ref>

{{multiple image
| align             = left
| direction         = horizontal
| header            = Other uses of fins
| header_align      = center
| header_background = 
| image1            = Dactyloptena orientalis.JPG
| width1            = 182
| alt1              = 
| caption1          = The [[Biology:Oriental flying gurnard|Oriental flying gurnard]] has large pectoral fins with [[Biology:Eyespot (mimicry)|eye spots]] which it displays to '''scare predators'''.
| image2            = Pelvicachromis taeniatus.jpg
| width2            = 194
| alt2              = 
| caption2          = During '''courtship''', the female [[Biology:Cichlid|cichlid]], ''[[Biology:Pelvicachromis taeniatus|Pelvicachromis taeniatus]]'', displays her visually arresting purple [[Biology:Pelvic fin|pelvic fin]].
| image3            = Xanthichthys ringens - pone.0010676.g191.png
| width3            = 238
| alt3              = 
| caption3          = Triggerfish squeeze into coral crevices to avoid predators, and '''lock''' themselves in place with the first spine of their dorsal fin.<ref>Schultz, Ken (2011) [https://books.google.com/books?id=09SA7lO-DJwC&dq=Triggerfish+spines+lock&pg=PA250 ''Ken Schultz's Field Guide to Saltwater Fish''] Page 250, John Wiley & Sons. {{ISBN|9781118039885}}.</ref>
| image4            = Humpback anglerfish.png
| width4            = 145
| alt4              = 
| caption4          = The first spine of the dorsal fin of the [[Biology:Anglerfish|anglerfish]] is modified so it functions like a fishing rod with a '''lure''' to attract prey.
| image5            = Echeneis naucrates.jpg
| width5            = 181
| alt5              = 
| caption5          = [[Biology:Remora|Remora]]s have modified first dorsal fins, which take the form of an oval, sucker-like organ with which they '''attach''' themselves to other marine organisms.
| image6            = Lionfish with Spread Pectoral Fins.jpg
| width6            = 181
| alt6              = 
| caption6          = Lionfish have venomous spines (fin rays) on their dorsal, pelvic and anal fins, which they use for '''defense'''.
}}
{{clear}}

==Evolution==

=== Evolution of paired fins ===

There are two prevailing hypotheses that have been historically debated as models for the evolution of paired fins in fish: the gill arch theory and the lateral fin-fold theory. The former, commonly referred to as the “Gegenbaur hypothesis,” was posited in 1870 and proposes that the “paired fins are derived from gill structures”.<ref>Goodrich, Edwin S. 1906. "Memoirs: Notes on the Development, Structure, and Origin of the Median and Paired Fins of Fish." Journal of Cell Science s2-50 (198): 333–76.</ref> This fell out of popularity in favor of the lateral fin-fold theory, first suggested in 1877, which proposes that paired fins budded from longitudinal, lateral folds along the epidermis just behind the gills.<ref name="Origin and Comparative Anatomy of t">{{cite journal | last1 = Brand | first1 = Richard A | year = 2008 | title = Origin and Comparative Anatomy of the Pectoral Limb | journal = Clinical Orthopaedics and Related Research | volume = 466 | issue = 3| pages = 531–42 | doi = 10.1007/s11999-007-0102-6 | pmid=18264841 | pmc=2505211}}</ref> There is weak support for both hypotheses in the fossil record and in embryology.<ref name=":0" /> However, recent insights from developmental patterning have prompted reconsideration of both theories in order to better elucidate the origins of paired fins.

==== Classical theories ====
Carl Gegenbaur's concept of the “Archipterygium” was introduced in 1876.<ref>Gegenbaur, C., F. J. Bell, and E. Ray Lankester. 1878. ''Elements of Comparative Anatomy. By Carl Gegenbaur ... Tr. by F. Jeffrey Bell ... The Translation Rev. and a Preface Written by E. Ray Lankester ...'' London,: Macmillan and Co.,.</ref> It was described as a gill ray, or “joined cartilaginous stem,” that extended from the gill arch. Additional rays arose from along the arch and from the central gill ray. Gegenbaur suggested a model of [[Biology:Homology|transformative homology]] – that all vertebrate paired fins and limbs were transformations of the Archipterygium. Based on this theory, paired appendages such as pectoral and pelvic fins would have differentiated from the branchial arches and migrated posteriorly. However, there has been limited support for this hypothesis in the fossil record both morphologically and phylogenically.<ref name=":0">{{cite journal | last1 = Coates | first1 = M. I. | year = 2003 | title = The Evolution of Paired Fins | journal = Theory in Biosciences | volume = 122 | issue = 2–3| pages = 266–87 | doi=10.1078/1431-7613-00087}}</ref> In addition, there was little to no evidence of an anterior-posterior migration of pelvic fins.<ref>Goodrich, Edwin S. 1906. "Memoirs: Notes on the Development, Structure, and Origin of the Median and Paired Fins of Fish." ''Journal of Cell Science'' s2-50 (198): 333–76.</ref> Such shortcomings of the gill-arch theory led to its early demise in favor of the lateral fin-fold theory proposed by St. George Jackson Mivart, [[Biography:Francis Maitland Balfour|Francis Balfour]], and James Kingsley Thacher.

The lateral fin-fold theory hypothesized that paired fins developed from lateral folds along the body wall of the fish.<ref name="Origin and Comparative Anatomy of t"/> Just as segmentation and budding of the median fin fold gave rise to the median fins, a similar mechanism of fin bud segmentation and elongation from a lateral fin fold was proposed to have given rise to the paired pectoral and pelvic fins. However, there was little evidence of a lateral fold-to-fin transition in the fossil record.<ref name="Evolutionary Developmental Biology">{{cite journal | last1 = Begemann | first1 = Gerrit | year = 2009 | title = Evolutionary Developmental Biology | journal = Zebrafish | volume = 6 | issue = 3| pages = 303–4 | doi = 10.1089/zeb.2009.0593 }}</ref> In addition, it was later demonstrated phylogenically that pectoral and pelvic fins arise from distinct evolutionary and mechanistic origins.<ref name=":0" />

==== Evolutionary developmental biology ====
{{See also|Evolutionary developmental biology}}Recent studies in the ontogeny and evolution of paired appendages have compared finless vertebrates – such as [[Biology:Lamprey|lamprey]]s – with chondricthyes, the most basal living vertebrate with paired fins.<ref>{{cite journal | last1 = Cole | first1 = Nicholas J. | last2 = Currie | first2 = Peter D. | year = 2007 | title = Insights from Sharks: Evolutionary and Developmental Models of Fin Development | journal = Developmental Dynamics | volume = 236 | issue = 9| pages = 2421–31 | doi = 10.1002/dvdy.21268 | pmid=17676641| s2cid = 40763215 | doi-access = free }}</ref> In 2006, researchers found that the same genetic programming involved in the segmentation and development of median fins was found in the development of paired appendages in [[Biology:Catshark|catshark]]s.<ref>{{cite journal | last1 = Freitas | first1 = Renata | last2 = Zhang | first2 = GuangJun | last3 = Cohn | first3 = Martin J. | year = 2006 | title = Evidence That Mechanisms of Fin Development Evolved in the Midline of Early Vertebrates | journal = Nature | volume = 442 | issue = 7106| pages = 1033–37 | doi = 10.1038/nature04984 | pmid = 16878142 | bibcode = 2006Natur.442.1033F | s2cid = 4322878 }}</ref>  Although these findings do not directly support the lateral fin-fold hypothesis, the original concept of a shared median-paired fin evolutionary developmental mechanism remains relevant.

A similar renovation of an old theory may be found in the developmental programming of chondricthyan gill arches and paired appendages. In 2009, researchers at the [[Organization:University of Chicago|University of Chicago]] demonstrated that there are shared molecular patterning mechanisms in the early development of the chondricthyan gill arch and paired fins.<ref>{{cite journal | last1 = Gillis | first1 = J. A. | last2 = Dahn | first2 = R. D. | last3 = Shubin | first3 = N. H. | year = 2009| title = Shared Developmental Mechanisms Pattern the Vertebrate Gill Arch and Paired Fin Skeletons | journal = Proceedings of the National Academy of Sciences | volume = 106 | issue = 14| pages = 5720–24 | doi = 10.1073/pnas.0810959106 | pmid = 19321424 | pmc=2667079| bibcode = 2009PNAS..106.5720G | doi-access = free }}</ref> Findings such as these have prompted reconsideration of the once-debunked gill-arch theory.<ref name="Evolutionary Developmental Biology"/>

=== From fins to limbs ===

Fish are the ancestors of all mammals, reptiles, birds and amphibians.<ref>[https://www.sciencedaily.com/releases/2008/09/080922090843.htm "Primordial Fish Had Rudimentary Fingers"] ''ScienceDaily'', 23 September 2008.</ref> In particular, terrestrial [[Biology:Tetrapod|tetrapod]]s (four-legged animals) evolved from fish and made their first forays onto land 400&nbsp;million years ago.<ref>{{cite book |last=Laurin |first=M. |title=How Vertebrates Left the Water |publisher=University of California Press |location=Berkeley, California, US |year=2010 |isbn=978-0-520-26647-6 |author-link=Michel Laurin }}</ref> They used paired pectoral and pelvic fins for locomotion. The pectoral fins developed into forelegs (arms in the case of humans) and the pelvic fins developed into hind legs.<ref>Hall, Brian K (2007) [https://books.google.com/books?id=Z0YWn5F9sWkC&q=Fins+into+Limbs ''Fins into Limbs: Evolution, Development, and Transformation''] University of Chicago Press. {{ISBN|9780226313375}}.</ref> Much of the genetic machinery that builds a walking limb in a tetrapod is already present in the swimming fin of a fish.<ref>[[Biography:Neil Shubin|Shubin, Neil]] (2009) [https://books.google.com/books?id=c008kdNwR1cC&q=%22Your+Inner+Fish%22 ''Your inner fish: A journey into the 3.5 billion year history of the human body''] Vintage Books. {{ISBN|9780307277459}}. [http://www.uctv.tv/search-details.aspx?showID=16412 ''UCTV'' interview]</ref><ref>Clack, Jennifer A (2012) [https://books.google.com/books?id=6Ztrhm8uLQ0C&q=%22Gaining+Ground%3A+the+Origin+and+Early+Evolution+of+Tetrapods%22 "From fins to feet"] Chapter 6, pages 187–260, ''in:'' ''Gaining Ground, Second Edition: The Origin and Evolution of Tetrapods'', Indiana University Press. {{ISBN|9780253356758}}.</ref>{{Quote box
| title = 
| quote = Aristotle recognised the distinction between analogous and homologous structures, and made the following prophetic comparison:
"Birds in a way resemble fishes. For birds have their wings in the upper part of their bodies and fishes have two fins in the front part of their bodies. Birds have feet on their underpart and most fishes have a second pair of fins in their under-part and near their front fins."
| source = – Aristotle, ''De incessu animalium''<ref>{{cite journal | last1 = Moore | first1 = John A | year = 1988 | title = [www.sicb.org/dl/saawok/449.pdf "Understanding nature—form and function"] Page 485 | journal = American Zoologist | volume = 28 | issue = 2| pages = 449–584 | doi=10.1093/icb/28.2.449| doi-access = free }}</ref>
| align = right
| salign = right
| width = 220px
}}[[File:Crossopterygii fins tetrapod legs.svg|thumb|180px|left|Comparison between A) the swimming fin of a [[Biology:Sarcopterygii|lobe-finned fish]] and B) the walking leg of a tetrapod. Bones considered to correspond with each other have the same color.]]
[[File:Ichthyosaurus BW.jpg|thumb|right|In a parallel but independent evolution, the ancient reptile {{extinct}}''Ichthyosaurus communis'' developed fins (or flippers) very similar to fish (or dolphins).]]

In 2011, researchers at Monash University in Australia used primitive but still living [[Biology:Lungfish|lungfish]] "to trace the evolution of pelvic fin muscles to find out how the load-bearing hind limbs of the tetrapods evolved."<ref>[https://www.sciencedaily.com/releases/2011/10/111004180106.htm Lungfish Provides Insight to Life On Land: 'Humans Are Just Modified Fish'] ''ScienceDaily'', 7 October 2011.</ref><ref>{{cite journal | last1 = Cole | first1 = NJ | last2 = Hall | first2 = TE | last3 = Don | first3 = EK | last4 = Berger | first4 = S | last5 = Boisvert | first5 = CA | display-authors = etal | year = 2011 | title = Development and Evolution of the Muscles of the Pelvic Fin | journal = PLOS Biology | volume = 9 | issue = 10| page = e1001168 | doi = 10.1371/journal.pbio.1001168 | pmid = 21990962 | pmc = 3186808 | doi-access = free }}</ref> Further research at the University of Chicago found bottom-walking lungfishes had already evolved characteristics of the walking gaits of terrestrial tetrapods.<ref>[https://www.sciencedaily.com/releases/2011/12/111212153117.htm A small step for lungfish, a big step for the evolution of walking"] ''ScienceDaily'', 13 December 2011.</ref><ref>{{cite journal | last1 = King | first1 = HM | last2 = Shubin | first2 = NH | last3 = Coates | first3 = MI | last4 = Hale | first4 = ME | year = 2011 | title = Behavioral evidence for the evolution of walking and bounding before terrestriality in sarcopterygian fishes | journal = Proceedings of the National Academy of Sciences | volume = 108 | issue = 52| pages = 21146–21151 | doi=10.1073/pnas.1118669109 | pmid=22160688 | pmc=3248479| bibcode = 2011PNAS..10821146K | doi-access = free }}</ref>

In a classic example of [[Biology:Convergent evolution|convergent evolution]], the pectoral limbs of [[Biology:Pterosaur|pterosaur]]s, [[Biology:Origin of avian flight|birds]] and [[Biology:Bat wing development|bats]] further evolved along independent paths into flying wings. Even with flying wings there are many similarities with walking legs, and core aspects of the genetic blueprint of the pectoral fin have been retained.<ref>{{cite journal | last1 = Shubin | first1 = N | last2 = Tabin | first2 = C | last3 = Carroll | first3 = S | year = 1997 | title = Fossils, genes and the evolution of animal limbs | url = http://genepath.med.harvard.edu/~tabin/Pdfs/Shubin.pdf | journal = Nature | volume = 388 | issue =  6643| pages = 639–648 | doi = 10.1038/41710 | pmid = 9262397 | url-status = dead | archive-url = https://web.archive.org/web/20120916105318/http://genepath.med.harvard.edu/~tabin/Pdfs/Shubin.pdf | archive-date = 2012-09-16 | bibcode = 1997Natur.388..639S | s2cid = 2913898 }}</ref><ref>[http://www.ucmp.berkeley.edu/vertebrates/flight/converge.html Vertebrate flight: The three solutions] University of California. Updated 29 September 2005.</ref>

The first mammals appeared during the [[Earth:Permian|Permian]] period (between 298.9 and 252.17&nbsp;million years ago). Several groups of these mammals started returning to the sea, including the cetaceans (whales, dolphins and porpoises). Recent DNA analysis suggests that cetaceans evolved from within the [[Biology:Even-toed ungulate|even-toed ungulate]]s, and that they share  a common ancestor with the [[Biology:Hippopotamus|hippopotamus]].<ref name="ScienceNews">{{Cite web | title = Scientists find missing link between the dolphin, whale and its closest relative, the hippo | date = 2005-01-25 | access-date = 2007-06-18 | url = http://www.sciencenewsdaily.org/story-2806.html | work = Science News Daily | url-status = dead | archive-url = https://web.archive.org/web/20070304214747/http://www.sciencenewsdaily.org/story-2806.html | archive-date = 2007-03-04 }}</ref><ref name="DNA">{{Cite journal | title = More DNA support for a Cetacea/Hippopotamidae clade: the blood-clotting protein gene gamma-fibrinogen | author = Gatesy, J. | journal = [[Biology:Molecular Biology and Evolution|Molecular Biology and Evolution]] | volume = 14 | pages = 537–543 | pmid = 9159931 | issue = 5 | date=1 May 1997 | doi=10.1093/oxfordjournals.molbev.a025790| doi-access = free }}</ref>  About 23&nbsp;million years ago another group of bearlike land mammals started returning to the sea. These were the [[Biology:Pinniped|seals]].<ref>{{
cite journal
| vauthors = Flynn JJ, Finarelli JA, Zehr S, Hsu J, Nedbal MA 
| title=Molecular phylogeny of the carnivora (mammalia): assessing the impact of increased sampling on resolving enigmatic relationships 
| journal=Systematic Biology
| year=2005
| volume=54
| pages=317–337
| pmid=16012099
| issue=2
| doi=10.1080/10635150590923326
| doi-access=free
}}</ref> What had become walking limbs in  cetaceans and seals evolved independently into new forms of swimming fins. The forelimbs became [[Biology:Flipper (anatomy)|flippers]], while the hindlimbs were either lost (cetaceans) or also modified into flipper (pinnipeds). In cetaceans, the tail gained  two fins at the end, called a [[Biology:Whale#Appendages|fluke]].<ref>Felts WJL [https://books.google.com/books?id=KyxELyTDlsQC&dq=whale+evolution+flipper+fluke&pg=PA255 "Some functional and structural characteristics of cetacean flippers and flukes"] Pages 255–275 ''in:'' Norris KS (ed.) ''Whales, Dolphins, and Porpoises'', University of California Press.</ref> Fish tails are usually vertical and move from side to side. Cetacean flukes are horizontal and move up and down, because cetacean spines bend the same way as in other mammals.<ref>[http://evolution.berkeley.edu/evolibrary/article/evograms_03 The evolution of whales] ''University of California Museum''. Retrieved 27 November 2012.</ref><ref>{{cite journal | last1 = Thewissen | first1 = JGM | last2 = Cooper | first2 = LN | last3 = George | first3 = JC | last4 = Bajpai | first4 = S | year = 2009 | title = From Land to Water: the Origin of Whales, Dolphins, and Porpoises | url = http://www.evolbiol.ru/large_files/whales.pdf | journal = Evo Edu Outreach | volume = 2 | issue = 2| pages = 272–288 | doi = 10.1007/s12052-009-0135-2 | s2cid = 11583496 | doi-access = free }}</ref>

[[File:Ichthyosaur vs dolphin.svg|left|thumb|Similar adaptations for fully aquatic lifestyle are found both in dolphins and ichthyosaurs.]]
[[Biology:Ichthyosaur|Ichthyosaur]]s are ancient reptiles that resembled dolphins. They first appeared about 245&nbsp;million years ago and disappeared about 90&nbsp;million years ago.
<blockquote>
"This sea-going reptile with terrestrial ancestors converged so strongly on fishes that it actually evolved a dorsal fin and tail fin for improved aquatic locomotion. These structures are all the more remarkable because they evolved from nothing — the ancestral terrestrial reptile had no hump on its back or blade on its tail to serve as a precursor."<ref name="Martill, 1993">Martill D.M. (1993). "Soupy Substrates: A Medium for the Exceptional Preservation of Ichthyosaurs of the Posidonia Shale (Lower Jurassic) of Germany". ''Kaupia - Darmstädter Beiträge zur Naturgeschichte'', '''2''' : 77-97.</ref></blockquote>
The biologist [[Biography:Stephen Jay Gould|Stephen Jay Gould]] said the ichthyosaur was his favorite example of [[Biology:Convergent evolution|convergent evolution]].<ref>Gould,Stephen Jay (1993) [https://books.google.com/books?id=_kOoVw0SIhUC "Bent Out of Shape"] in ''Eight Little Piggies: Reflections in Natural History''. Norton, 179–94. {{ISBN|9780393311396}}.</ref>

Fins or flippers of varying forms and at varying locations (limbs, body, tail) have also evolved in a number of other tetrapod groups, including diving birds such as penguins (modified from wings), sea turtles (forelimbs modified into flippers), mosasaurs (limbs modified into flippers), and sea snakes (vertically expanded, flattened tail fin).

==Robotic fins==
[[File:RobotFishCharlie.jpg|thumb|right|In the 1990s, the [[CIA]] built a robotic catfish called ''Charlie'', designed to collect underwater intelligence undetected.<ref>{{cite web|title=Charlie: CIA's Robotic Fish |url=https://www.cia.gov/library/video-center/video-transcripts/charlie-cias-robotic-fish.html |date= Jun 4, 2013 |archive-url=https://web.archive.org/web/20130816050550/https://www.cia.gov/library/video-center/video-transcripts/charlie-cias-robotic-fish.html|url-status=dead|archive-date=16 August 2013|website=Central Intelligence Agency |access-date=12 December 2016}}</ref>
{{externalimage
|float=center
|width=200px
|video1=[https://www.youtube.com/watch?v=u8tfES8gImc AquaPenguin] - ''Festo, YouTube''
|video2=[https://www.youtube.com/watch?v=-vT-oidWyXE AquaRay] - ''Festo, YouTube''
|video3=[https://www.youtube.com/watch?v=mKMN-dz8n3k AquaJelly] - ''Festo, YouTube''
|video4=[https://www.youtube.com/watch?v=TKeVVKGEDLc AiraCuda ] - ''Festo, YouTube''
|video5=}}]]

The use of fins for [[Biology:Aquatic locomotion|the propulsion]] of aquatic animals can be remarkably effective. It has been calculated that some fish can achieve a [[Engineering:Marine propulsion|propulsive]] efficiency greater than 90%.<ref name=Sfakiotakis>{{cite journal | last1 = Sfakiotakis | first1 = M | last2 = Lane | first2 = DM | last3 = Davies | first3 = JBC | year = 1999 | title = Review of Fish Swimming Modes for Aquatic Locomotion | 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 | journal = IEEE Journal of Oceanic Engineering | volume = 24 | issue =  2| pages = 237–252 | doi = 10.1109/48.757275 | 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 | citeseerx = 10.1.1.459.8614 | bibcode = 1999IJOE...24..237S | s2cid = 17226211 }}</ref> Fish can accelerate and maneuver much more effectively than [[Engineering:Boat|boat]]s or [[Engineering:Submarine|submarine]], and produce less water disturbance and noise. This has led to biomimetic studies of underwater robots which attempt to emulate the locomotion of aquatic animals.<ref>{{cite web|url=http://rjmason.com/ramblings/robotFishMarket.html|author=Richard Mason|title=What is the market for robot fish?|url-status=dead|archive-url=https://web.archive.org/web/20090704021443/http://rjmason.com/ramblings/robotFishMarket.html|archive-date=2009-07-04}}</ref> An example is the Robot Tuna built by the [http://fibo.kmutt.ac.th/ Institute of Field Robotics], to analyze and mathematically model [[Biology:Fish locomotion#Thunniform locomotion|thunniform motion]].<ref>{{cite web|url=http://fibo.kmutt.ac.th/project/eng/current_research/fish.html|publisher=Institute of Field Robotics|title=Fish Robot|author=Witoon Juwarahawong|access-date=2007-10-25 |archive-url = https://web.archive.org/web/20071104081550/http://fibo.kmutt.ac.th/project/eng/current_research/fish.html |archive-date = 2007-11-04}}</ref> In 2005, the Sea Life London Aquarium displayed three robotic fish created by the computer science department at the [[Organization:University of Essex|University of Essex]]. The fish were designed to be autonomous, swimming around and avoiding obstacles like real fish. Their creator claimed that he was trying to combine "the speed of tuna, acceleration of a pike, and the navigating skills of an eel."<ref>{{cite web|url=http://cswww.essex.ac.uk/staff/hhu/HCR-Group.html#Entertainment|publisher=Human Centred Robotics Group at Essex University|title=Robotic fish powered by Gumstix PC and PIC|access-date=2007-10-25}}</ref><ref name="cnn">{{Cite web
|url=http://edition.cnn.com/2005/TECH/10/07/spark.fish
|title=Robotic fish make aquarium debut
|work=cnn.com
|publisher=CNN
|date=10 October 2005
|access-date=12 June 2011
}}</ref><ref name="london_times1">
{{Cite news
|url=http://www.thetimes.co.uk/tto/business/industries/leisure/article2172983.ece
|title=Merlin Entertainments tops up list of London attractions with aquarium buy
|last=Walsh
|first=Dominic
|work=thetimes.co.uk
|publisher=Times of London
|date=3 May 2008
|access-date=12 June 2011
}}</ref>

The ''AquaPenguin'', developed by Festo of Germany, copies the streamlined shape and propulsion by front flippers of [[Biology:Penguin|penguin]]s.<ref>[http://www.controlengeurope.com/article/24663/For-Festo--Nature-Shows-the-Way.aspx For Festo, Nature Shows the Way] ''Control Engineering'', 18 May 2009.</ref><ref>[http://www.gizmag.com/bionic-penguins-fly-through-water--and-air/11545/ Bionic penguins fly through water... and air] ''Gizmag'', 27 April 2009.</ref> Festo also developed ''AquaRay'',<ref>[http://www.technovelgy.com/ct/science-fiction-news.asp?newsnum=2249 Festo AquaRay Robot] ''Technovelgy'', 20 April 2009.</ref> ''AquaJelly''<ref>[http://www.engineeringtv.com/video/The-AquaJelly-Robotic-Jellyfish The AquaJelly Robotic Jellyfish from Festo] ''Engineering TV'', 12 July 2012.</ref> and ''AiraCuda'',<ref>[http://www.theengineer.co.uk/in-depth/analysis/lightweight-robots-festos-flying-circus/1009421.article Lightweight robots: Festo's flying circus] {{Webarchive|url=https://web.archive.org/web/20150919071715/http://www.theengineer.co.uk/in-depth/analysis/lightweight-robots-festos-flying-circus/1009421.article |date=19 September 2015 }} ''The Engineer'', 18 July 2011.</ref> respectively emulating the locomotion of manta rays, jellyfish and barracuda.

In 2004, [[Biography:Hugh Herr|Hugh Herr]] at MIT prototyped a biomechatronic robotic fish with a living [[Engineering:Actuator|actuator]] by surgically transplanting muscles from frog legs to the robot and then making the robot swim by pulsing the muscle fibers with electricity.<ref>{{cite journal | last1 = Huge Herr | first1 = D. Robert G | title = A Swimming Robot Actuated by Living Muscle Tissue | journal = Journal of NeuroEngineering and Rehabilitation | volume = 1 | issue = 1| page = 6 | doi = 10.1186/1743-0003-1-6 | pmid = 15679914 | pmc=544953 | date=Oct 2004 | doi-access = free }}</ref><ref>[http://science.howstuffworks.com/biomechatronics4.htm How Biomechatronics Works] ''HowStuffWorks''/ Retrieved 22 November 2012.</ref>

Robotic fish offer some research advantages, such as the ability to examine an individual part of a fish design in isolation from the rest of the fish. However, this risks oversimplifying the biology so key aspects of the animal design are overlooked. Robotic fish also allow researchers to vary a single parameter, such as flexibility or  a specific motion control. Researchers can directly measure forces, which is not easy to do in live fish. "Robotic devices also facilitate three-dimensional kinematic studies and correlated hydrodynamic analyses, as the location of the locomotor surface can be known accurately. And, individual components of a natural motion (such as outstroke vs. instroke of a flapping appendage) can be programmed separately, which is certainly difficult to achieve when working with a live animal."<ref>{{cite journal | last1 = Lauder | first1 = G. V. | year = 2011 | title = Swimming hydrodynamics: ten questions and the technical approaches needed to resolve them | url = http://www.people.fas.harvard.edu/~glauder/reprints_unzipped/Lauder.Exp.Fluids.2011.pdf | journal = Experiments in Fluids | volume = 51 | issue = 1| pages = 23–35 | doi=10.1007/s00348-009-0765-8| bibcode = 2011ExFl...51...23L | s2cid = 890431 }}</ref>

{{clear}}

==See also==
* Cephalopod fin
* Fin and flipper locomotion
* [[Biology:Fish locomotion|Fish locomotion]]
* [[Biology:Polydactyly in early tetrapods|Polydactyly in early tetrapods]]
* [[Engineering:RoboTuna|RoboTuna]]
* Shark fin soup
* Tradeoffs for locomotion in air and water
* [[Physics:Undulatory locomotion|Undulatory locomotion]]

==References==

===Citations===
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{{Reflist|33em|refs=

<ref name="Johanson2006">{{cite journal | last1 = Johanson | first1 = Zerina | last2 = Long | first2 = John A. | last3 = Talent | first3 = John A. | last4 = Janvier | first4 = Philippe | last5 = Warren | first5 = James W. | year = 2006 | title = Oldest Coelacanth, from the Early Devonian of Australia | journal = Biology Letters | volume = 2 | issue = 3 | pages = 443–46 | doi = 10.1098/rsbl.2006.0470 | pmid = 17148426 | pmc = 1686207}}</ref>

<ref name="Fricke1987">{{cite journal | last1 = Fricke | first1 = Hans | last2 = Reinicke | first2 = Olaf | last3 = Hofer | first3 = Heribert | last4 = Nachtigall | first4 = Werner | year = 1987 | title = Locomotion of the Coelacanth Latimeria Chalumnae in Its Natural Environment | journal = Nature | volume = 329 | issue = 6137| pages = 331–33 | doi=10.1038/329331a0 | bibcode=1987Natur.329..331F| s2cid = 4353395 }}</ref>
}}

===Bibliography===
{{Refbegin}}
* {{cite book|last=Hamlett|first=William C.|title=Sharks, skates, and rays: the biology of elasmobranch fishes|publisher=The Johns Hopkins University Press|page=56|year=1999|edition=1st|isbn=978-0-8018-6048-5|url=https://books.google.com/books?id=ON-sPP5rowwC&q=shark%20fin%20%20ceratotrichia%20supported&pg=PA56}}
{{Refend}}

==Further reading==
* Hall, Brian K (2007) [https://books.google.com/books?id=Z0YWn5F9sWkC&q=Fins+into+Limbs ''Fins into Limbs: Evolution, Development, and Transformation''] University of Chicago Press. {{ISBN|9780226313375}}.
* Helfman G, Collette BB, Facey DE and Bowen BW (2009) [https://web.archive.org/web/20150602082907/http://limnology.wisc.edu/courses/zoo510/2009/helfman_ch8.pdf "Functional morphology of locomotion and feeding"] Chapter 8, pp.&nbsp;101–116. In:''The Diversity of Fishes: Biology'', John Wiley & Sons. {{ISBN|9781444311907}}.
* {{cite journal | last1 = Lauder | first1 = GV |  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 }}
* {{cite journal | last1 = Lauder | first1 = GV | last2 = Drucker | first2 = EG | year = 2004 | title = Morphology and experimental hydrodynamics of fish fin control surfaces | url = http://www.people.fas.harvard.edu/~glauder/reprints_unzipped/Lauder.Drucker.2004.pdf | journal = Journal of Oceanic Engineering | volume = 29 | issue = 3| pages = 556–571 | doi=10.1109/joe.2004.833219| bibcode = 2004IJOE...29..556L | s2cid = 36207755 }}

==External links==
* [http://www.amonline.net.au/palaeontology/pdf/johanson2005lethaia.pdf Homology of fin lepidotrichia in osteichthyan fishes]
* [http://www.earthlife.net/fish/fins.html The Fish's Fin] Earthlife Web
* [http://science.howstuffworks.com/environmental/green-tech/remediation/robot-fish.htm Can robot fish find pollution?] ''HowStuffWorks''. Accessed 30 January 2012.

{{Fins, limbs and wings|state=expanded}}
{{Diversity of fish}}

[[Category:Fish anatomy]]

{{Sourceattribution|Fish fin}}