{{Short description|Subfamily of fishes}} {{Automatic taxobox | image = GambianMudskippers.jpg | image_caption = Atlantic mudskipper (''Periophthalmus barbarus'') in The Gambia | taxon = Oxudercinae | authority = Gunther 1861<ref name = Zootaxa>{{cite journal | author1 = Richard van der Laan | author2 = William N. Eschmeyer | author3 = Ronald Fricke | name-list-style = amp |year=2014 | title = Family-group names of Recent fishes | journal = Zootaxa | volume = 3882 | issue =2 | pages = 001–230| doi = 10.11646/zootaxa.3882.1.1 | pmid = 25543675 | doi-access = free }}</ref> | subdivision_ranks = Genera | subdivision = ''Apocryptes''<br/> ''Apocryptodon''<br/> ''Boleophthalmus''<br/> ''Oxuderces''<br/> ''Parapocryptes''<br/> ''Periophthalmodon''<br/><!-- ZoolSci23:1043. --> ''Periophthalmus''<br/><!-- ZoolSci23:1043,25:946. --> ''Pseudapocryptes''<br/> ''Scartelaos''<br/> ''Zappa'' | synonyms = * Periophthalminae }} '''Mudskippers''' are any of the 25 extant species of amphibious fish from the subfamily '''Oxudercinae''' of the goby family Oxudercidae.<ref name = Nelson5>{{cite web | url = https://81a86d48-a-62cb3a1a-s-sites.googlegroups.com/site/fotw5th/home/FotW5Classification.pdf?attachauth=ANoY7crnPmFXqnJpmRlpzLSdqx8GmsCmFXNBj8fAYuPuhFBvCfHo4TahH7eM_yruTzHI27nZRRWWJPRR7U9HopPBRlQK8iW_73EG6FVke6aUjl20fgZXiChDnl-xqMl4L2I-wHwV7D4qcPAQI1vSV6YfFYAm5qb7t5w0rJ_ierkZ91ezIvpQ_5f0kSbFiUx-YYGXP1US1GbwSf-G7sRx4XEikm73VqVA0idVnlkaFjzI53bkuIQY0OQ%3D&attredirects=0 | title = Classification of fishes from Fishes of the World 5th Edition | author1 = Nelson, JS | author2 = Grande, TC | author3 = Wilson, MVH | name-list-style = amp | year = 2016 | access-date = 10 May 2018}}</ref> They are known for their unusual body shapes, preferences for semiaquatic habitats, limited terrestrial locomotion and jumping, and the ability to survive prolonged periods of time both in and out of water.
Mudskippers can grow up to {{cvt|30|cm}} long, and most are a brownish green colour that ranges anywhere from dark to light. During mating seasons, the males will also develop brightly coloured spots in order to attract females, which can be red, green, or blue. Unlike other fish, the mudskipper's eyes protrude from the top of its flat head. Another notable feature is that their side pectoral fins are located more forward and underneath their elongated bodies. These fins are jointed and function similarly to limbs, which allow the mudskipper to crawl from place to place. Although they have the typical body form of any other gobiid fish, pectoral fins allow the mudskipper to actively "skip" across muddy surfaces (hence the common name) and even climb low-hanging tree branches and scrub. Mudskippers can leap distances of up to {{convert|61|cm}} by laterally flexing and pushing with their tails.{{citation needed|date=September 2020}}
==Taxonomy== Oxudercinae is sometimes classified within the family Gobiidae (gobies).<ref name="Murdy1989">{{cite journal|author=Murdy EO|title=A Taxonomic Revision and Cladistic Analysis of the Oxudercine Gobies (Gobiidae: Oxudercinae)|journal=Records of the Australian Museum|year=1989|volume=Suppl 11|pages=1–93|doi=10.3853/j.0812-7387.11.1989.93|doi-access=free}}</ref> Recent molecular studies do not support this classification, as oxudercine gobies appear to be paraphyletic relative to amblyopine gobies (Gobiidae: Amblyopinae), thus being included in a distinct "''Periophthalmus'' lineage", together with amblyopines.<ref name="Agorreta et al. 2013">{{cite journal|author1=Agorreta A. |author2=San Mauro D. |author3=Schliewen U. |author4=Rüber L. |name-list-style=amp |title=Molecular phylogenetics of Gobioidei and phylogenetic placement of European gobies|journal=Molecular Phylogenetics and Evolution|year=2013|volume=69 | issue = 3 |pages=619–633|doi=10.1016/j.ympev.2013.07.017 |pmid=23911892|hdl=10261/123985 |hdl-access=free }}</ref> Mudskippers can be defined as oxudercine gobies that are "fully terrestrial for some portion of the daily cycle" (character 24 in Murdy, 1989<ref name="Murdy1989" />). This would define the species of the genera ''Boleophthalmus'', ''Periophthalmodon'', ''Periophthalmus'', and ''Scartelaos'' as "mudskippers". However, field observations of ''Zappa confluentus'' suggest that this monotypic genus should be included in the definition.<ref name="Polgar et al. 2010">{{cite journal|author1=Polgar G. |author2=Sacchetti A. |author3=Galli P. |name-list-style=amp |title=Differentiation and adaptive radiation of amphibious gobies (Gobiidae: Oxudercinae) in semi-terrestrial habitats|journal=Journal of Fish Biology|year=2010|volume=77|issue=7 |pages=1645–1664|doi=10.1111/j.1095-8649.2010.02807.x|pmid=21078024 |doi-access=free}}</ref>
==Behavior== Mudskippers typically live in burrows in intertidal habitats, and exhibit unique adaptations to this environment that are not found in most intertidal fishes, which typically survive the retreat of the tide by hiding under wet seaweed or in tide pools.<ref name="Graham1997">{{cite book|editor=Graham JB|title=Air–breathing Fishes. Evolution, Diversity and Adaptation|publisher=Academic Press|location=San Diego California|year=1997}}</ref> These burrows are most often characterised by their smooth and vaulted ceilings. The way the males dig these burrows has been found to be directly linked to their ability to survive submerged in almost anoxic water. It has also been found to play a crucial role in the development of the eggs within the burrow. Mudskippers are quite active when out of water, feeding and interacting with one another, for example, to defend their territories and court potential partners. Once the male has completed digging his burrow he will resurface and will begin attempting to attract a female through assorted yet typical displays. These displays consist of body undulations, different postures and energetic movements. Once the female has made her choice she will then proceed to follow the male into the burrow where she will lay hundreds of eggs and allow them to be fertilized. After fertilization occurs, the period of cohabitation between the male and female is rather short. Eventually, the female will leave and it is the male that ends up guarding the egg-filled burrow from predators.{{Citation needed|date=November 2023}}
Mudskippers are amphibious. When leaving the water and moving into a more dry environment on land, they are still able to breathe using water that is trapped inside their large gill chambers. They are also able to absorb oxygen from the lining of their mouth and throat, allowing them to stay out of water for long periods of time. It has been discovered that they spend up to three quarters of their life on land. They are found in tropical, subtropical, and temperate regions, including the Indo-Pacific and the Atlantic coast of Africa.{{Citation needed|date=January 2021}}
==Adaptations== [[File:Periophthalmus gracilis.jpg|right|thumb|''Periophthalmus gracilis'' (from Malaysia to northern Australia)]] right|thumb|''Periophthalmus barbarus'' (from western Africa) [[File:Periophthalmus argentilineatus 01.JPG|thumb|Barred mudskipper (''Periophthalmus argentilineatus'')]] Compared with fully aquatic gobies, these specialised fish present a range of anatomical and ethological adaptations that allow them to move effectively on land as well as in the water.<ref name=Harris1960>{{cite journal|author=Harris VA|title=On the locomotion of the mudskipper ''Periophthalmus koelreuteri'' (Pallas): Gobiidae|journal=Proceedings of the Zoological Society of London|volume=134|pages=107–135|year=1960|doi=10.1111/j.1469-7998.1960.tb05921.x}}</ref><ref name=Pace&Gibbs2009>{{cite journal|vauthors=Pace CM, Gibb AC| title=Mudskipper pectoral fin kinematics in aquatic and terrestrial environments|journal=Journal of Experimental Biology|volume=212|issue=14|pages=2279–2286|year=2009|doi=10.1242/jeb.029041|pmid=19561218|doi-access=free}}</ref>
===Terrestrial movement=== As their name implies, these fish use their fins to move around in a series of skips.
{{quote|Although mudskippers' fins do not have a joint homologous to the elbow, the joint between the radials and the fin rays serves a functionally analogous role.|''Integrative and Comparative Biology''<ref>{{cite journal |author1=S. M. Kawano |author2=R. W. Blob |title=Propulsive Forces of Mudskipper Fins and Salamander Limbs during Terrestrial Locomotion: Implications for the Invasion of Land | journal=Integrative and Comparative Biology |volume=53 |issue=2 |date=August 2, 2013 |pages=283–294 |doi= 10.1093/icb/ict051|pmid=23667046|doi-access=free }}</ref>}}
{{quote|The mudskipper pectoral fin differs from most actinopterygian fishes in that the radials of the mudskipper pectoral fin are elongated and protrude from the body wall. This unusual morphology creates a pectoral fin with two fin segments (the radials and the rays) and two movable hinge joints: a 'shoulder' joint where the cleithrum meets the radials and an 'intra-fin' joint where the radials meet the rays.<ref name="Harris1960" /> In addition, ... the abductor superficialis muscle of the pectoral fin is divided into two sections (rather than being a single muscle, as is common with the rest of the Oxudercinae gobies) with one section inserting on the dorsal rays and the other section inserting on the ventral rays.|''The Journal of Experimental Biology''<ref>{{cite journal |vauthors=Pace CM, Gibb AC|title=Mudskipper pectoral fin kinematics in aquatic and terrestrial environments |url=http://jeb.biologists.org/content/212/14/2279.full.pdf | journal=The Journal of Experimental Biology |volume=212 |issue=14 |date=July 15, 2009 |pages=2279–2286 |doi= 10.1242/jeb.029041|pmid=19561218|s2cid=18176905 |doi-access=free }}</ref>}}
===Breathing=== [[File:Mudskipper india.jpg|thumb|Mudskipper at Point Calimere Sanctuary, Tamil Nadu, India]] [[File:Periophthalmus novemradiatus ( mudskipper ).jpg|thumb|Mudskipper at Coringa Mangrove Sanctuary, Andhra Pradesh, India]] thumb|right|''Periophthalmodon septemradiatus'' territorial defense call and jumping ability<ref name=Polgaretal2011>{{cite journal|vauthors=Polgar G, Malavasi S, Cipolato G, Georgalas V, Clack JA, Torricelli P |title=Acoustic Communication at the Water's Edge: Evolutionary Insights from a Mudskipper|journal=PLOS ONE|volume=6|issue=6|article-number=e21434|year=2011|doi=10.1371/journal.pone.0021434|pmid=21738663|pmc=3125184|bibcode=2011PLoSO...621434P|doi-access=free}}</ref> Mudskippers have the ability to breathe through their skin and the lining of their mouth (the mucosa) and throat (the pharynx); this is only possible when the mudskippers are wet, limiting them to humid habitats and requiring that they keep themselves moist. The ability to breathe through their skin is associated with increased capillary density in their skin.<ref name=CorushandZhang2022>{{cite journal|vauthors=Corush J, Zhang J |title=One size does not fit all: Variation in anatomical traits associated with emersion behavior in mudskippers (Gobiidae: Oxudercinae)|journal=Frontiers in Ecology and Evolution|volume=10|pages= 967067–967075|year=2022|doi=10.3389/fevo.2022.967067 |doi-access=free }}</ref> This mode of breathing, similar to that employed by amphibians, is known as cutaneous respiration.<ref name=Graham1997/> Another important adaptation that aids breathing while out of water is their enlarged gill chambers, where they retain a bubble of air. These chambers close tightly when the fish is above water, due to a ventromedial valve of the gill slit, keeping the gills moist, and allowing them to function while exposed to air. Gill filaments are stiff and do not coalesce when out of water.<ref name=Graham1997/>
===Diet=== The different species have adapted to various diets on the mudflats. ''Boleophthalmus boddarti'' is detritivorous, while others will eat small crabs, insects, snails and even other mudskippers.<ref>[https://books.google.com/books?id=FFXRAgAAQBAJ&dq=mudskipper+detritivores+carnivorous+crabs+insects&pg=PT138 Ecology of Kalimantan: Indonesian Borneo]</ref>
===Burrowing=== Digging deep burrows in soft sediments allows the fish to thermoregulate,<ref name=Tytler1983>{{cite journal|vauthors=Tytler P, Vaughan T |title=Thermal Ecology of the Mudskippers ''Periophthalmus koelreuteri'' (Pallas) and ''Boleophthalmus boddaerti'' (Pallas), of Kuwait Bay|journal=Journal of Fish Biology|volume=23|issue=3|pages=327–337|year=1983|doi=10.1111/j.1095-8649.1983.tb02912.x}}</ref> avoid marine predators during the high tide when the fish and burrow are submerged,<ref name=Sasekumar1994>{{cite conference|vauthors=Sasekumar A, Chong VC, Lim KH, Singh HR |title=The Fish Community of Matang Mangrove Waters, Malaysia|book-title=Proceedings, Third ASEAN-Australia Symposium on Living Coastal Resources. Research papers|veditors=Sudara S, Wilkinson CR, Chou LM |publisher=Chulalonghorn University|location=Bangkok|year=1994|volume=2|pages=457–464}}</ref> and lay their eggs.<ref name=Brillet1969>{{cite journal|author=Brillet C|title=Etude du comportement constructeur des poissons amphibies Periophthalmidae|journal=Terre et la Vie|volume=23|issue=4|pages=496–520|year=1969|language=fr}}</ref> When the burrow is submerged, several mudskipper species maintain an air pocket inside it, which allows them to breathe in conditions of very low oxygen concentration.<ref name=Ishimatsu1998>{{cite journal|vauthors=Ishimatsu A, Hishida Y, Takita T, Kanda T, Oikawa S, Takeda T, Khoo KH |title=Mudskipper Store Air in Their Burrows|journal=Nature|volume=391|issue=6664|pages=237–238|year=1998|doi=10.1038/34560|bibcode=1998Natur.391..237I|s2cid=4429394}}</ref><ref name=Ishimatsu2000>{{cite journal|vauthors=Ishimatsu A, Takeda T, Kanda T, Oikawa S, Khoo KH |title=Burrow environment of mudskippers in Malaysia|journal=Journal of Biosciences|volume=11|issue=1–2|pages=17–28|year=2000}}</ref><ref name=Lee2005>{{cite journal|vauthors=Lee HJ, Martinez CA, Hertzberg KJ, Hamilton AL, Graham JB |title=Burrow air phase maintenance and respiration by the mudskipper ''Scartelaos histophorus'' (Gobiidae: Oxudercinae)|journal=The Journal of Experimental Biology|volume=208|issue=Pt 1|pages=169–177|year=2005|doi=10.1242/jeb.01361|pmid=15601887|doi-access=free}}</ref>
===Ammonia regulation=== To reduce toxic ammonia production, mudskippers can suppress amino acid breakdown when exposed to air.<ref name="Ip 768–782">{{Cite journal|last1=Ip|first1=Y. K.|last2=Chew|first2=S. F.|last3=Randall|first3=D. J.|date=2004-09-01|title=Five Tropical Air‐Breathing Fishes, Six Different Strategies to Defend against Ammonia Toxicity on Land|url=https://www.journals.uchicago.edu/doi/10.1086/422057|journal=Physiological and Biochemical Zoology|volume=77|issue=5|pages=768–782|doi=10.1086/422057|pmid=15547795|s2cid=20545085|issn=1522-2152|url-access=subscription}}</ref> Another method they use involves the partial breakdown of amino acids leading to the production of alanine, which also reduces ammonia production.<ref name="Ip 768–782"/>
Mudskippers can reduce the membrane permeability of their skin and acidify the water in their burrows to reduce levels of ammonia from the environment.<ref>{{Cite journal|last1=Randall|first1=D. J.|last2=Ip|first2=Y. K.|last3=Chew|first3=S. F.|last4=Wilson|first4=J. M.|date=September 2004|title=Air Breathing and Ammonia Excretion in the Giant Mudskipper, Periophthalmodon schlosseri|url=http://www.journals.uchicago.edu/doi/10.1086/423745|journal=Physiological and Biochemical Zoology|language=en|volume=77|issue=5|pages=783–788|doi=10.1086/423745|pmid=15547796|s2cid=36864021|issn=1522-2152|url-access=subscription}}</ref><ref>{{Cite journal|last1=Randall|first1=D. J.|last2=Wilson|first2=J. M.|last3=Peng|first3=K. W.|last4=Kok|first4=T. W. K.|last5=Kuah|first5=S. S. L.|last6=Chew|first6=S. F.|last7=Lam|first7=T. J.|last8=Ip|first8=Y. K.|date=1999-12-01|title=The mudskipper, Periophthalmodon schlosseri, actively transports NH 4 + against a concentration gradient|url=https://journals.physiology.org/doi/full/10.1152/ajpregu.1999.277.6.R1562|journal=American Journal of Physiology. Regulatory, Integrative and Comparative Physiology|volume=277|issue=6|pages=R1562–R1567|doi=10.1152/ajpregu.1999.277.6.R1562|pmid=10600900|s2cid=29598011 |issn=0363-6119|url-access=subscription}}</ref>
===Blinking=== Mudskippers evolved the ability to blink independently from terrestrial tetrapods. Their eyes are located high on their head compared to other gobies, and they blink by lowering their eyes as a membrane called the dermal cup rises to cover them. Although other fully aquatic goby species do not have the ability to blink, mudskippers did not evolve different muscles or glands to blink with; their blinking is accomplished with the same muscles in a different configuration. Rather than having specialized glands to produce eye lubricant, the fluid film on their cornea is likely composed of mucus secreted by their skin and water from their environment, possibly stored in the infraorbital space behind the dermal cup membrane. Mudskippers likely evolved blinking in response to conditions of terrestrial life, such as to keep their eyes wet out of water (they blink more frequently in high evaporation conditions and only when colliding with things in water) and to clean and protect the eye from debris, which may adhere to the eye or approach at a faster, more dangerous speed when in air versus when in water. Their eyes are not elevated when they are still juveniles, which are fully aquatic.<ref name="blinking">{{cite journal |last1=Aiello |first1=Brett R. |last2=Bhamla |first2=M. Saad |last3=Gau |first3=Jeff |last4=Morris |first4=John G. L. |last5=Bomar |first5=Kenji |last6=da Cunha |first6=Shashwati |last7=Fu |first7=Harrison |last8=Laws |first8=Julia |last9=Minoguchi |first9=Hajime |last10=Sripathi |first10=Manognya |last11=Washington |first11=Kendra |last12=Wong |first12=Gabriella |last13=Shubin |first13=Neil H. |last14=Sponberg |first14=Simon |last15=Stewart |first15=Thomas A. |date=April 24, 2023 |title=The origin of blinking in both mudskippers and tetrapods is linked to life on land |journal=PNAS |volume=120 |issue=18 |article-number=e2220404120 |doi=10.1073/pnas.2220404120 |pmid=37094121 |pmc=10160996 |doi-access=free}}</ref>
==Species== The genus ''Periophthalmus'' is by far the most diverse and widespread genus of mudskipper. Eighteen species have been described.<ref name=Larson2004>{{cite journal|vauthors=Larson HK, Takita T |title=Two new species of ''Periophthalmus'' (Teleostei: Gobiidae: Oxudercinae) from northern Australia, and a re-diagnosis of ''Periophthalmus novaeguineaensis''|journal=The Beagle, Records of the Museums and Art Galleries of the Northern Territory|volume=20|pages=175–185|year=2004|doi=10.5962/p.286325|s2cid=131712323 |url=https://www.biodiversitylibrary.org/part/286325|doi-access=free}}</ref><ref name=Jaafar2009>{{cite journal|vauthors=Jaafar Z, Perrig M, Chou LM |title=''Periophthalmus variabilis'' (Teleostei: Gobiidae: Oxudercinae), a valid species of mudskipper, and a re-diagnosis of ''Periophthalmus novemradiatus''|journal=Zoological Science|volume=26|issue=4|pages=309–314|year=2009|doi=10.2108/zsj.26.309|pmid=19798926|s2cid=31647216}}</ref><ref name=Jaafar2008>{{cite journal|vauthors=Jaafar Z, Larson HL |title=A new species of mudskipper, ''Periophthalmus takita'' (Teleostei: Gobiidae: Oxudercinae), from Australia, with a key to the genus|journal= Zoological Science|volume=25|issue=9|pages=946–952|year=2008|doi=10.2108/zsj.25.946|pmid=19267605|s2cid=10659541}}</ref> ''Periophthalmus argentilineatus'' is one of the most widespread and well-known species. It can be found in mangrove ecosystems and mudflats of East Africa and Madagascar east through the Sundarbans of Bengal, Southeast Asia to Northern Australia, southeast China, Taiwan, and the Ryukyus, to Samoa and Tonga Islands.<ref name=Murdy1989/> It grows to a length of about 9.5 cm <ref name=Murdy1989/> and is a carnivorous opportunist feeder. It feeds on small prey such as small crabs and other arthropods.<ref name=Milward1974>{{cite book|last=Milward|first=NE|title=Studies on the taxonomy, ecology and physiology of Queensland mudskippers|publisher=University of Queensland|location=Brisbane|year=1974|edition=unpubl. Ph.D. dissertation}}</ref> However, a recent molecular study suggests that ''P. argentilineatus'' is in fact a complex of species, with at least three separate lineages, one in East Africa, and two in the Indo-Malayan region.<ref name=Polgaretal.2014>{{cite journal|vauthors=Polgar G, Zane L, Babbucci M, Barbisan F, Patarnello T, Rüber L, Papetti C |title=Phylogeography and demographic history of two widespread Indo-Pacific mudskippers (Gobiidae: ''Periophthalmus'').|journal=Molecular Phylogenetics and Evolution|volume=73|pages=161–176|year=2014|doi=10.1016/j.ympev.2014.01.014|pmid=24486991}}</ref> Another species, ''Periophthalmus barbarus'', is the only oxudercine goby that inhabits the coastal areas of western Africa.<ref name=Murdy1989/>
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==References== {{Reflist}}
==External links== * [http://www.fishbase.org/Summary/FamilySummary.cfm?ID=405 FishBase entry on Gobiidae] * [http://www.themudskipper.org The Mudskipper: a website on mudskippers] or [http://www.mudskipper.it The Mudskipper] * [https://www.flickr.com/photos/danieltrim/sets/72157635970409156/ Mudskipper photos] on Flickr
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Category:Mudskippers Category:Gobiiformes Category:Amphibious fish Category:Articles containing video clips Category:Walking fish