Cavefish or cave fish is a generic term for fresh and brackish water fish adapted to life in caves and other underground habitats. Related terms are subterranean fish, troglomorphic fish, troglobitic fish, stygobitic fish, phreatic fish and hypogean fish.[1][2]

The more than 200 scientifically described species of obligate cavefish are found on all continents, except Antarctica.[3][4] Although widespread as a group, many cavefish species have very small ranges and are seriously threatened.[5][6] Cavefish are members of a wide range of families and do not form a monophyletic group.[7] Typical adaptations found in cavefish are reduced eyes and pigmentation.[1][2]

Cyprinidae - Phreatichthys andruzzii
Phreatichthys andruzzii showing the pale colour and lack of eyes typical of cavefish. The large red spot on the head is the blood-filled gills, visible through the semi-transparent gill cover


Typhleotris madgascarensis
As typical of cavefish, Typhleotris madagascariensis is an opportunistic feeder on various invertebrates[8][9]

Many aboveground fish may enter caves on occasion, but obligate cavefish (fish that require underground habitats) are extremophiles with a number of unusual adaptations known as troglomorphism. In some species, notably the Mexican tetra, shortfin molly, Oman garra, Indoreonectes evezardi and a few catfish, both "normal" aboveground and cavefish forms exist.[10][11][12][13]

Many adaptions seen in cavefish are aimed at surviving in a habitat with little food.[1] Living in darkness, pigmentation and eyes are useless, or an actual disadvantage because of their energy requirements, and therefore typically reduced in cavefish.[14][15][16] Other examples of adaptations are larger fins for more energy-efficient swimming, and a loss of scales and swim bladder.[17][18] The loss can be complete or only partial, for example resulting in small or incomplete (but still existing) eyes, and eyes can be present in the earliest life stages but degenerated by the adult stage.[19] In some cases, "blind" cavefish may still be able to see: Juvenile Mexican tetras of the cave form are able to sense light via certain cells in the pineal gland (pineal eye),[20] and Congo blind barbs are photophobic, despite only having retinas and optical nerves that are rudimentary and located deep inside the head, and completely lacking a lens.[21] In the most extreme cases, the lack of light has changed the circadian rhythm (24-hour internal body clock) of the cavefish. In the Mexican tetra of the cave form and in Phreatichthys andruzzii the circadian rhythm lasts 30 hours and 47 hours, respectively.[22][23] This may help them to save energy.[22] Without sight, other senses are used and these may be enhanced. Examples include the lateral line for sensing vibrations,[24][25] mouth suction to sense nearby obstacles (comparable to echolocation),[26] and chemoreception (via smell and taste buds).[27][28] Although there are cavefish in groups known to have electroreception (catfish and South American knifefish), there is no published evidence that this is enhanced in the cave-dwellers.[29] The level of specialized adaptations in a cavefish is generally considered to be directly correlated to the amount of time it has been restricted to the underground habitat: Species that recently arrived show few adaptations and species with the largest number of adaptations are likely the ones that have been restricted to the habitat for the longest time.[30]

Some fish species that live buried in the bottom of aboveground waters, live deep in the sea or live in deep rivers have adaptations similar to cavefish, including reduced eyes and pigmentation.[31][32][33]

Cryptotora thamicola
The waterfall climbing cavefish has several adaptions that allow it to climb and "walk" in a tetrapod-like fashion[34]

Cavefish are quite small with most species being less than 10 cm (4 in) long and very few able to surpass 20 cm (8 in).[16] At up to about 40 cm (16 in), the blind cave eel is the longest known cavefish.[35] The very limited food resources in the habitat likely prevents larger cavefish species from existing and also means that cavefish in general are opportunistic feeders, taking whatever is available.[15][30] In their habitat, cavefish are often the top predators, feeding on smaller cave-living invertebrates, or are detritivores without enemies.[18] Cavefish typically have low metabolic rates and may be able to survive long periods of starvation. A captive Phreatobius cisternarum did not feed for a year, but remained in good condition.[36] The cave form of the Mexican tetra can build up unusually large fat reserves by "binge eating" in periods where food is available, which then (together with its low metabolic rate) allows it to survive without food for months, much longer than the aboveground form of the species.[37]

In the dark habitat, certain types of displays are reduced in cavefish,[17] but in other cases they have become stronger, shifting from displays that are aimed at being seen to displays aimed at being felt via water movement. For example, during the courtship of the cave form of the Mexican tetra the pair produce turbulence through exaggerated gill and mouth movements, allowing them to detect each other.[16] In general, cavefish are slow growers and slow breeders.[2] Breeding behaviors among cavefish vary extensively, and there are both species that are egg-layers and ovoviparous species that give birth to live young.[16] Uniquely among fish, the genus Amblyopsis brood their eggs in the gill chambers (somewhat like mouthbrooders).[38]


Dama ciega blanca
The Mexican blind brotula and other cave-dwelling brotulas are among the few species that live in anchialine habitas

Although many cavefish species are restricted to underground lakes, pools or rivers in actual caves, some are found in aquifers and may only be detected by humans when artificial wells are dug into this layer.[36][39] Most live in areas with low (essentially static) or moderate water current,[1][30] but there are also species in places with very strong current, such as the waterfall climbing cavefish.[40] Underground waters are often very stable environments with limited variations in temperature (typically near the annual average of the surrounding region), nutrient levels and other factors.[1][41] Organic compounds generally only occur in low levels and rely on outside sources, such as contained in water that enters the underground habitat from outside, aboveground animals that find their way into caves (deliberately or by mistake) and guano from bats that roost in caves.[1][41][42] Cavefish are primarily restricted to freshwater.[1] A few species, notably the cave-dwelling viviparous brotulas, Luciogobius gobies, Milyeringa sleeper gobies and the blind cave eel, live in anchialine caves and several of these tolerate various salinities.[1][43][44][45][46]

Range and diversity

The more than 200 scientifically described obligate cavefish species are found in most continents, but there are strong geographic patterns and the species richness varies.[3] The vast majority of species are found in the tropics or subtropics.[47] Cavefish are strongly linked to regions with karst, which commonly result in underground sinkholes and subterranean rivers.[1][7]

With more than 120 described species, by far the greatest diversity is in Asia, followed by more than 30 species in South America and about 30 species in North America.[3][7] In contrast, only 9 species are known from Africa, 5 from Oceania,[7] and 1 from Europe.[4][48] On a country level, China has the greatest diversity with more than 80 species, followed by Brazil with more than 20 species. India, Mexico, Thailand and the United States of America each have 9–12 species.[1][3][49] No other country has more than 5 cavefish species.[7][50][51]

Amblyopsis hoosieri 29330
The Hoosier cavefish from Indiana in the United States was only described in 2014[52]

Being underground, many places where cavefish may live have not been thoroughly surveyed. New cavefish species are described with some regularity and undescribed species are known.[5][7] As a consequence, the number of known cavefish species has risen rapidly in recent decades. In the early 1990s only about 50 species were known, in 2010 about 170 species were known,[53] and by 2015 this had surpassed 200 species.[3] It has been estimated that the final number might be around 250 obligate cavefish species.[54] For example, the first cavefish in Europe, a Barbatula stone loach, was only discovered in 2015 in Southern Germany.[4][48] Conversely, their unusual appearance means that some cavefish already attracted attention in ancient times. The oldest known description of an obligate cavefish, involving Sinocyclocheilus hyalinus, is almost 500 years old.[47]

Obligate cavefish are known from a wide range of families: Characidae (characids), Balitoridae (hillstream loaches), Cobitidae (true loaches), Cyprinidae (carps and allies), Nemacheilidae (stone loaches), Amblycipitidae (torrent catfishes), Astroblepidae (naked sucker-mouth catfishes), Callichthyidae (armored catfishes), Clariidae (airbreathing catfishes), Heptapteridae (heptapterid catfishes), Ictaluridae (ictalurid catfishes), Kryptoglanidae (kryptoglanid catfish), Loricariidae (loricariid catfishes), Phreatobiidae (phreatobiid catfishes), Trichomycteridae (pencil catfishes), Sternopygidae (glass knifefishes), Amblyopsidae (U.S. cavefishes), Bythitidae (brotulas), Poeciliidae (live-bearers), Synbranchidae (swamp eels), Cottidae (true sculpins), Butidae (butid gobies), Eleotridae (sleeper gobies), Milyeringidae (blind cave gobies), and Gobiidae (gobies).[1][7][55] Many of these families are only very distantly related and do not form a monophyletic group, showing that adaptations to a life in caves has happened numerous times among fish. As such, their similar adaptions are examples of convergent evolution and the descriptive term "cavefish" is an example of folk taxonomy rather than scientific taxonomy.[7] Strictly speaking some Cyprinodontidae (pupfish) are also known from sinkhole caves, famously including the Devils Hole pupfish, but these lack the adaptations (e.g., reduced eyes and pigmentation) typically associated with cavefish.[1] Additionally, species from a few families such as Chaudhuriidae (earthworm eels), Glanapteryginae and Sarcoglanidinae live buried in the bottom of aboveground waters, and can show adaptions similar to traditional underground-living (troglobitic) fish.[36][31][56][57] It has been argued that such species should be recognized as a part of the group of troglobitic fish.[3]


As of 2019, the following underground-living fish species with various levels of troglomorphism (ranging from complete loss of eyes and pigment, to only a partial reduction of one of these) are known.[1][3][49][58] Prietella phreatophila, the only species with underground populations in more than one country,[59] is listed twice. Excluded from the table are species that live buried in the bottom of aboveground waters (even if they have troglomorphic-like features) and undescribed species.

Family Species Country Year of description Notes
Characidae Astyanax aeneus Mexico 1860 Species includes both aboveground and belowground forms (aboveground also in Central America). Sometimes considered a part of Astyanax mexicanus[60][61][62]
Characidae Astyanax mexicanus (blind cave tetra) Mexico 1853 Species includes both aboveground and belowground forms (aboveground also in United States). Cave form sometimes considered a separate species, A. jordani[62]
Characidae Stygichthys typhlops (Brazilian blind characid) Brazil 1965
Cyprinidae Anchicyclocheilus halfibindus China 1992 Sometimes considered a species in the genus Sinocyclocheilus,[58] or a synonym of Sinocyclocheilus microphthalmus[63]
Cyprinidae Barbopsis devecchi (Somalian blind barb) Somalia 1926
Cyprinidae Caecobarbus geertsii (Congo blind barb) DR Congo 1921
Cyprinidae Caecocypris basimi (Haditha cavefish) Iraq 1980
Cyprinidae Garra barreimiae (Omani blind cavefish) Oman 1956 Species includes both aboveground and belowground forms (aboveground also in the United Arab Emirates). A population in the United Arab Emirates has been reported to be underground,[49] but this is incorrect[3][64]
Cyprinidae Garra dunsirei (Tawi Atair garra) Oman 1987
Cyprinidae Garra lorestanensis Iran 2016
Cyprinidae Garra tashanensis Iran 2016
Cyprinidae Garra typhlops (Iran cave barb) Iran 1944 Formerly in its own genus Iranocypris[65]
Cyprinidae Longanalus macrochirous China 2006
Cyprinidae Neolissochilus subterraneus Thailand 2003
Cyprinidae Phreatichthys andruzzii Somalia 1924
Cyprinidae Poropuntius speleops Thailand 1991
Cyprinidae Sinocyclocheilus albeoguttatus China 1998
Cyprinidae Sinocyclocheilus altishoulderus China 1992
Cyprinidae Sinocyclocheilus aluensis China 2005
Cyprinidae Sinocyclocheilus anatirostris (duck-billed golden-line fish) China 1986
Cyprinidae Sinocyclocheilus angularis (gold-colored angle fish) China 1990
Cyprinidae Sinocyclocheilus anophthalmus (eyeless golden-line fish) China 1988
Cyprinidae Sinocyclocheilus anshuiensis China 2013
Cyprinidae Sinocyclocheilus aquihornes China 2007
Cyprinidae Sinocyclocheilus biangularis China 1996
Cyprinidae Sinocyclocheilus bicornutus China 1997
Cyprinidae Sinocyclocheilus brevibarbatus China 2009
Cyprinidae Sinocyclocheilus broadihornes China 2007
Cyprinidae Sinocyclocheilus cyphotergous China 1988
Cyprinidae Sinocyclocheilus flexuosdorsalis China 2012
Cyprinidae Sinocyclocheilus furcodorsalis (crossed-fork back golden-line fish) China 1997
Cyprinidae Sinocyclocheilus guanyangensis China 2016
Cyprinidae Sinocyclocheilus huanjiangensis China 2010
Cyprinidae Sinocyclocheilus hugeibarbus China 2003
Cyprinidae Sinocyclocheilus hyalinus (hyaline fish) China 1993
Cyprinidae Sinocyclocheilus jinxiensis China 2012 Proposed moved to monotypic genus Pseudosinocyclocheilus in 2016[66]
Cyprinidae Sinocyclocheilus jiuxuensis China 2003
Cyprinidae Sinocyclocheilus lingyunensis China 2000
Cyprinidae Sinocyclocheilus longibarbatus China 1989
Cyprinidae Sinocyclocheilus longifinus China 1996
Cyprinidae Sinocyclocheilus luolouensis China 2013
Cyprinidae Sinocyclocheilus luopingensis China 2002
Cyprinidae Sinocyclocheilus macrophthalmus China 2001
Cyprinidae Sinocyclocheilus macroscalus China 2000
Cyprinidae Sinocyclocheilus maculatus China 2000
Cyprinidae Sinocyclocheilus maitianheensis China 1992
Cyprinidae Sinocyclocheilus malacopterus China 1985
Cyprinidae Sinocyclocheilus mashanensis China 2010
Cyprinidae Sinocyclocheilus microphthalmus (small eye golden-line fish) China 1989
Cyprinidae Sinocyclocheilus multipunctatus China 1931
Cyprinidae Sinocyclocheilus oxycephalus China 1985
Cyprinidae Sinocyclocheilus purpureus China 1985
Cyprinidae Sinocyclocheilus qiubeiensis China 2002
Cyprinidae Sinocyclocheilus rhinocerous China 1994
Cyprinidae Sinocyclocheilus robustus China 1988
Cyprinidae Sinocyclocheilus tianeensis China 2003
Cyprinidae Sinocyclocheilus tianlinensis China 2004
Cyprinidae Sinocyclocheilus tileihornes China 2003
Cyprinidae Sinocyclocheilus xunlensis China 2004
Cyprinidae Sinocyclocheilus yishanensis China 1992
Cyprinidae Speolabeo hokhanhi Vietnam 2018
Cyprinidae Speolabeo musaei Laos 2011 Formerly in genus Bangana[67]
Cyprinidae Troglocyclocheilus khammouanensis Laos 1999
Cyprinidae Typhlobarbus nudiventris China 1982
Cyprinidae Typhlogarra widdowsoni (Iraq blind barb) Iraq 1955
Balitoridae Cryptotora thamicola (waterfall climbing cavefish) Thailand 1988
Cobitidae Bibarba parvoculus China 2015
Cobitidae Cobitis damlae Turkey 2014
Cobitidae Protocobitis anteroventris China 2013
Cobitidae Protocobitis polylepis China 2008
Cobitidae Protocobitis typhlops China 1993
Nemacheilidae Barbatula barbatula (stone loach) Germany 1758 Aboveground populations widespread in Europe. Belowground population only discovered in 2015 and tentatively included in this species based on genetic evidence. Only known cavefish in Europe[4]
Nemacheilidae Claea dabryi China 1874 Traditionally in genus Schistura or Triplophysa.[68][69] Species includes both aboveground and belowground populations; the latter sometimes recognized as a separate subspecies microphthalmus.[58]
Nemacheilidae Draconectes narinosus Vietnam 2012
Nemacheilidae Eidinemacheilus proudlovei Iraq 2016
Nemacheilidae Eidinemacheilus smithi (Zagroz blind loach) Iran 1976 Formerly in genus Noemacheilus or Paracobitis[70]
Nemacheilidae Heminoemacheilus hyalinus China 1996
Nemacheilidae Indoreonectes evezardi India 1872 Species includes both aboveground and belowground forms[71]
Nemacheilidae Nemacheilus troglocataractus (blind cave loach) Thailand 1989
Nemacheilidae Oreonectes acridorsalis China 2013
Nemacheilidae Oreonectes anophthalmus China 1981
Nemacheilidae Oreonectes barbatus China 2013
Nemacheilidae Oreonectes daqikongensis China 2016
Nemacheilidae Oreonectes donglanensis China 2013
Nemacheilidae Oreonectes duanensis China 2013
Nemacheilidae Oreonectes elongatus China 2012
Nemacheilidae Oreonectes furcocaudalis China 1987
Nemacheilidae Oreonectes guananensis China 2011
Nemacheilidae Oreonectes luochengensis China 2011
Nemacheilidae Oreonectes macrolepis China 2009
Nemacheilidae Oreonectes microphthalmus China 2008
Nemacheilidae Oreonectes shuilongensis China 2016
Nemacheilidae Oreonectes translucens China 2006
Nemacheilidae Schistura deansmarti Thailand 2003
Nemacheilidae Schistura jarutanini Thailand 1990
Nemacheilidae Schistura kaysonei Laos 2002
Nemacheilidae Schistura larketensis India 2017
Nemacheilidae Schistura lingyunensis China 1997 Sometimes in genus Triplophysa[68]
Nemacheilidae Schistura mobbsi Vietnam 2012
Nemacheilidae Schistura oedipus Thailand 1988
Nemacheilidae Schistura papulifera India 2007
Nemacheilidae Schistura sijuensis India 1987
Nemacheilidae Schistura spekuli Vietnam 2004
Nemacheilidae Schistura spiesi Thailand 2003
Nemacheilidae Speonectes tiomanensis Malaysia 1990 Formerly in genus Sundoreonectes[68]
Nemacheilidae Triplophysa aluensis China 2000
Nemacheilidae Triplophysa dongganensis China 2013
Nemacheilidae Triplophysa fengshanensis China 2013
Nemacheilidae Triplophysa gejiuensis China 1979
Nemacheilidae Triplophysa huanjiangensis China 2011
Nemacheilidae Triplophysa jiarongensis China 2012
Nemacheilidae Triplophysa langpingensis China 2013
Nemacheilidae Triplophysa lihuensis China 2012
Nemacheilidae Triplophysa longibarbata China 1998 Includes Paracobitis maolanensis and P. posterodorsalus as synonyms,[68] which may be valid species[58]
Nemacheilidae Triplophysa luochengensis China 2017
Nemacheilidae Triplophysa macrocephala China 2011
Nemacheilidae Triplophysa qiubeiensis China 2008
Nemacheilidae Triplophysa rosa China 2005
Nemacheilidae Triplophysa shilinensis China 1992
Nemacheilidae Triplophysa tianeensis China 2004
Nemacheilidae Triplophysa xiangshuingensis China 2004
Nemacheilidae Triplophysa xiangxiensis China 1986
Nemacheilidae Triplophysa yunnanensis China 1990
Nemacheilidae Troglocobitis starostini (Starostin's loach) Turkmenistan 1983
Amblycipitidae Xiurenbagrus dorsalis China 2014
Astroblepidae Astroblepus pholeter Ecuador 1962
Astroblepidae Astroblepus riberae Peru 1994
Callichthyidae Aspidoras mephisto Brazil 2017 Formerly included in aboveground species A. albater[72]
Clariidae Clarias cavernicola (golden cave catfish) Angola 1936
Clariidae Horaglanis abdulkalami India 2012
Clariidae Horaglanis alikunhii India 2004
Clariidae Horaglanis krishnai (Indian blind catfish) India 1950
Clariidae Uegitglanis zammaranoi Somalia 1923
Heptapteridae Pimelodella kronei Brazil 1907
Heptapteridae Pimelodella spelaea Brazil 2004
Heptapteridae Rhamdia enfurnada Brazil 2005
Heptapteridae Rhamdia guasarensis Venezuela 2004
Heptapteridae Rhamdia laluchensis (La Lucha blind catfish) Mexico 2003
Heptapteridae Rhamdia laticauda typhla Belize 1982 Other subspecies found in aboveground habitats in Mexico and Central America[1][73]
Heptapteridae Rhamdia macuspanensis (Olmec blind catfish) Mexico 1998
Heptapteridae Rhamdia quelen urichi Trinidad 1926 Other subspecies found widely in aboveground habitats in South and Central America[74]
Heptapteridae Rhamdia reddelli (blind whiskered catfish) Mexico 1984
Heptapteridae Rhamdia zongolicensis (Zongolica catfish) Mexico 1993
Heptapteridae Rhamdiopsis krugi Brazil 2010
Ictaluridae Prietella lundbergi (phantom blindcat) Mexico 1995
Ictaluridae Prietella phreatophila (Mexican blindcat) Mexico 1954 Listed twice (once for each country)
Ictaluridae Prietella phreatophila (Mexican blindcat) United States 1954 Listed twice (once for each country)
Ictaluridae Satan eurystomus (widemouth blindcat) United States 1947
Ictaluridae Trogloglanis pattersoni (toothless blindcat) United States 1919
Kryptoglanidae Kryptoglanis shajii India 2011 Found both underground and aboveground (not known to differ in appearance)[75]
Loricariidae Ancistrus cryptophthalmus Brazil 1987
Loricariidae Ancistrus formoso Brazil 1997
Loricariidae Ancistrus galani Venezuela 1994
Phreatobiidae Phreatobius cisternarum Brazil 1905
Phreatobiidae Phreatobius dracunculus Brazil 2007
Phreatobiidae Phreatobius sanguijuela Bolivia 2007
Siluridae Pterocryptis buccata (cave sheatfish) Thailand 1998 Species includes both aboveground and belowground forms[13]
Siluridae Pterocryptis cucphuongensis Vietnam 1978
Trichomycteridae Glaphyropoma spinosum Brazil 2008
Trichomycteridae Ituglanis bambui Brazil 2004
Trichomycteridae Ituglanis boticario Brazil 2015
Trichomycteridae Ituglanis epikarsticus Brazil 2004
Trichomycteridae Ituglanis mambai Brazil 2008
Trichomycteridae Ituglanis passensis Brazil 2002
Trichomycteridae Ituglanis ramiroi Brazil 2004
Trichomycteridae Silvinichthys bortayro Argentina 2005
Trichomycteridae Trichomycterus dali Brazil 2011
Trichomycteridae Trichomycterus chaberti Bolivia 1968
Trichomycteridae Trichomycterus itacarambiensis Brazil 1996
Trichomycteridae Trichomycterus rosablanca Colombia 2018
Trichomycteridae Trichomycterus rubbioli Brazil 2012
Trichomycteridae Trichomycterus sandovali Colombia 2006
Trichomycteridae Trichomycterus santanderensis Colombia 2007
Trichomycteridae Trichomycterus sketi Colombia 2010
Trichomycteridae Trichomycterus spelaeus Venezuela 2001
Trichomycteridae Trichomycterus uisae (trepador) Colombia 2008
Sternopygidae Eigenmannia vicentespelaea Brazil 1996
Amblyopsidae Amblyopsis hoosieri (Hoosier cavefish) United States 2014
Amblyopsidae Amblyopsis rosae (Ozark cavefish) United States 1898
Amblyopsidae Amblyopsis spelaea (northern cavefish) United States 1842
Amblyopsidae Forbesichthys agassizii (spring cavefish) United States 1872 Found belowground, but also nearby in aboveground waters during the night[1][76]
Amblyopsidae Speoplatyrhinus poulsoni (Alabama cavefish) United States 1974
Amblyopsidae Typhlichthys subterraneus (southern cavefish) United States 1859 Possibly a species complex and T. eigemanni may be a valid species[77]
Bythitidae Diancistrus typhlops Indonesia 2009
Bythitidae Lucifuga dentata (toothed Cuban cusk-eel) Cuba 1858
Bythitidae Lucifuga lucayana (Lucaya cave brotula) Bahamas 2006
Bythitidae Lucifuga simile Cuba 1981
Bythitidae Lucifuga spelaeotes (New Providence cusk-eel) Bahamas 1970
Bythitidae Lucifuga subterranea (Cuban cusk-eel) Cuba 1858
Bythitidae Lucifuga teresinarum Cuba 1988
Bythitidae Ogilbia galapagosensis (Galapagos cuskeel) Ecuador 1965 Arguably not a true cavefish, as places it inhabits also can be described as lagoon crevices[1]
Bythitidae Typhliasina pearsei (Mexican blind brotula) Mexico 1938
Poeciliidae Poecilia mexicana (cave molly) Mexico 1863 Species includes both aboveground and belowground forms (aboveground also in Central America)[10]
Synbranchidae Monopterus digressus India 2002
Synbranchidae Monopterus eapeni India 1991
Synbranchidae Monopterus roseni India 1998
Synbranchidae Ophisternon candidum (blind cave eel) Australia 1962
Synbranchidae Ophisternon infernale (blind swamp eel) Mexico 1938
Cottidae C. bairdicognatus species complex (mottled sculpin/slimy sculpin) United States 1850/1836 Aboveground forms relatively widespread in North America and Siberia, underground form only in Pennsylvania[78]
Cottidae Cottus carolinae (banded sculpin) United States 1861 Aboveground forms relatively widespread in the United States, underground form only in West Virginia[79][80]
Cottidae Cottus specus (grotto sculpin) United States 2013 Formerly included in C. carolinae[80]
Butidae Bostrychus microphthalmus Indonesia 2005 The family Butidae was formerly considered a subfamily of Eleotridae[3]
Butidae Oxyeleotris caeca Papua New Guinea 1996 The family Butidae was formerly considered a subfamily of Eleotridae[3]
Butidae Oxyeleotris colasi Indonesia 2013 Has mistakenly been reported to occur in Papua New Guinea,[3] but it is from Western New Guinea, the Indonesian part of the island.[81] The family Butidae was formerly considered a subfamily of Eleotridae[3]
Eleotridae Caecieleotris morrisi (Oaxaca cave sleeper) Mexico 2016
Milyeringidae Milyeringa brooksi Australia 2010 The family Milyeringidae was formerly considered a subfamily of Eleotridae[82]
Milyeringidae Milyeringa justitia (Barrow cave gudgeon) Australia 2013 The family Milyeringidae was formerly considered a subfamily of Eleotridae[82]
Milyeringidae Milyeringa veritas (blind gudgeon) Australia 1945 The family Milyeringidae was formerly considered a subfamily of Eleotridae[82]
Milyeringidae Typhleotris madagascariensis Madagascar 1933 The family Milyeringidae was formerly considered a subfamily of Eleotridae[83]
Milyeringidae Typhleotris mararybe Madagascar 2012 The family Milyeringidae was formerly considered a subfamily of Eleotridae[83]
Milyeringidae Typhleotris pauliani Madagascar 1959 The family Milyeringidae was formerly considered a subfamily of Eleotridae[83]
Gobiidae Caecogobius cryptophthalmus Philippines 1991
Gobiidae Caecogobius personatus Philippines 2019
Gobiidae Glossogobius ankaranensis Madagascar 1994
Gobiidae Luciogobius albus Japan 1940
Gobiidae Luciogobius pallidus Japan 1940


Astyanax mexicanus 01
The cave form of the Mexican tetra is easily bred in captivity and the only cavefish widely available to aquarists

Although cavefish as a group are found throughout large parts of the world, many cavefish species have tiny ranges (often restricted to a single cave or cave system) and are seriously threatened. In 1996, more than 50 species were recognized as threatened by the IUCN and many, including several that are rare, have not been accessed at all.[2] For example, the critically endangered Alabama cavefish is only found in the Key Cave and the entire population has been estimated at less than 100 individuals,[84] while the critically endangered golden cave catfish only is found in the Aigamas cave in Namibia and has an estimated population of less than 400 individuals.[85] The Haditha cavefish from Iraq and the Oaxaca cave sleeper from Mexico may already be extinct, as recent surveys have failed to find them.[86][87] In some other cases, such as the Brazilian blind characid which went unrecorded by ichthyologists from 1962 to 2004, the apparent "rarity" was likely because of a lack of surveys in its range and habitat, as locals considered it relatively common until the early 1990s (more recently, this species appears to truly have declined significantly).[39] Living in very stable environments, cavefish are likely more vulnerable to changes in the water (for example, temperature or oxygen) than fish of aboveground habitats which naturally experience greater variations.[41] The main threats to cavefish are typically changes in the water level (mainly through water extraction or drought), habitat degradation and pollution, but in some cases introduced species and collection for the aquarium trade also present a threat.[5][6] Cavefish often show little fear of humans and can sometimes be caught with the bare hands.[18] Most cavefish lack natural predators, although larger cavefish may feed on smaller individuals,[18] and cave-living crayfish, crabs, giant water bugs and spiders have been recorded feeding on a few species of cavefish.[88][89][90][91]

Caves in some parts of the world have been protected, which can safeguard the cavefish.[52] In a few cases such as the Omani blind cavefish (Oman garra), zoos have initiated breeding programs as a safeguard.[12] In contrast to the rarer species, the cave form of the Mexican tetra is easily bred in captivity and widely available to aquarists.[62][92] This is the most studied cavefish species and likely also the most studied cave organism overall.[93] As of 2006, only six other cavefish species have been bred in captivity, typically by scientists.[54]

See also


  1. ^ a b c d e f g h i j k l m n o p Romero, Aldemaro, editor (2001). The Biology of Hypogean Fishes. Developments in Environmental Biology of Fishes. ISBN 978-1402000768
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Alabama cavefish

The Alabama cavefish (Speoplatyrhinus poulsoni), is a critically endangered species of amblyopsid cavefish found only in underground pools in Key Cave, located in northwestern Alabama, United States in the Key Cave National Wildlife Refuge. It was discovered underneath a colony of gray bats in 1967 and scientifically described in 1974.On any single visit to the cave, no more than 10 individuals of this fish have been observed, and scientists estimate fewer than 100 are left. This fish is believed to be the rarest species of cavefish in the United States and one of the rarest of all freshwater fish. It exists in a fragile ecosystem based on nutrient-rich guano of the gray bat. Researchers have failed to find the fish in any other location.


The Amblyopsidae are a fish family commonly referred to as cavefish, blindfish, or swampfish. They are small freshwater fish found in the dark environments of caves (underground lakes, pools, rivers and streams), springs and swamps in the eastern half of the United States. Like other troglobites, most amblyopsids exhibit adaptations to these dark environments, including the lack of functional eyes and the absence of pigmentation. More than 200 species of cavefishes are known, but only six of these are in the family Amblyopsidae. One of these, Forbesichthys agassizii, spends time both underground and aboveground. A seventh species in this family, Chologaster cornuta, is not a cave-dweller but lives in aboveground swamps.

Blind cave eel

The blind cave eel (Ophisternon candidum) is a species of fish in the family Synbranchidae. It is endemic to subterranean waters in the Cape Range, Australia. Like other cavefish such as Milyeringa (the only other vertebrates restricted to subterranean waters in Australia), the blind cave eel is entirely blind and lacks pigmentation. It is listed as vulnerable under the Australian Environment Protection and Biodiversity Conservation Act 1999. Reaching a length of 40 cm (16 in), it is the longest known cavefish. In its history of being listed by the IUCN since 1988, it has not been well known hence the Data Deficient status.

Caecocypris basimi

Caecocypris basimi, the Haditha cavefish, is a species of cyprinid fish endemic to Iraq, only occurring in aquifers near Haditha. This cavefish is the only member of its genus. The species is classed as Critically endangered, possibly extinct, by the IUCN, as there have been no records since 1983 despite a comprehensive survey in 2012. The primary threat is water extraction, which has lowered the groundwater level.The cavefish Typhlogarra widdowsoni is found in the same place and it has also drastically declined, but it is not as rare as Caecocypris basimi. The only other known cavefish in Iraq is Eidinemacheilus proudlovei.The holotype of Caecocypris basimi, collected by Dr. Basim M Al Azzawi in 1977, is deposited at the British Museum of Natural History and other specimens are at the Australian Museum.

Eidinemacheilus smithi

Eidinemacheilus smithi, also known as the Zagroz blind loach, is a species of loach in the family Nemacheilidae. This cavefish is endemic to an aquifer in the Karun River drainage in the Zagros Mountains of Iran.There are three other known cavefish species in Iran: Garra lorestanensis, G. tashanensis and G. typhlops.

Garra barreimiae

Garra barreimiae, the Oman garra, is a species of ray-finned fish in the family Cyprinidae. It is found in the mountains of northern Oman and in the United Arab Emirates. Most populations inhabit wadis, streams, pools and springs, but one population lives underground in caves, is known as Omani blind cave fish, and has lost its sight and pigmentation. The only other cave fish in the Arabian Peninsula is the Tawi Atair garra (G. dunsirei), but it has normal eyes.

Hoosier cavefish

The Hoosier cavefish (Amblyopsis hoosieri) is a subterranean species of blind fish from southern Indiana in the United States. Described in 2014, A. hoosieri was the first new species of amblyopsid cavefish to be discovered in 40 years.

Mexican tetra

The Mexican tetra or blind cave fish (Astyanax mexicanus) is a freshwater fish of the family Characidae of the order Characiformes. The type species of its genus, it is native to the Nearctic ecozone, originating in the lower Rio Grande and the Neueces and Pecos Rivers in Texas, as well as the central and eastern parts of Mexico.Growing to a maximum total length of 12 cm (4.7 in), the Mexican tetra is of typical characin shape, with unremarkable, drab coloration. Its blind cave form, however, is notable for having no eyes or pigment; it has a pinkish-white color to its body (resembling an albino).This fish, especially the blind variant, is reasonably popular among aquarists.A. mexicanus is a peaceful species that spends most of its time in midlevel water above the rocky and sandy bottoms of pools and backwaters of creeks and rivers of its native environment. Coming from a subtropical climate, it prefers water with 6.5–8 pH, a hardness of up to 30 dGH, and a temperature range of 20 to 25 °C (68 to 77 °F). In the winter, some populations migrates to warmer waters. Its natural diet consists of crustaceans, insects, and annelids, although in captivity it is omnivorous.The Mexican tetra has been treated as a subspecies of A. fasciatus, but this is not widely accepted. Additionally, the blind cave form is sometimes recognized as a separate species, A. jordani, but this directly contradicts phylogenetic evidence.

Northern cavefish

The northern cavefish or northern blindfish, Amblyopsis spelaea, is found in caves through Kentucky and southern Indiana. It is listed as a threatened species in the United States and the IUCN lists the species as near threatened.

During a 2013 study of Amblyopsis spelaea, scientists found that the species was divided into two distinct evolutionary lineages: one north of the Ohio River, in Indiana, and one south of the river, in Kentucky. The southern population retained the name A. spelaea and the northern was re-designated Amblyopsis hoosieri in a 2014 paper published in the journal ZooKeys. Neither species is found north of the White River, flowing east to west south of Bedford, Indiana.

Ozark Cavefish National Wildlife Refuge

The Ozark Cavefish National Wildlife Refuge is a 40-acre (16-ha) National Wildlife Refuge located in Lawrence County, Missouri, 20 mi (32 km) west of Springfield. The United States Fish and Wildlife Service acquired the land in 1991 to protect the endangered Ozark cavefish.

Ozark cavefish

The Ozark cavefish, Amblyopsis rosae, is a small subterranean freshwater fish native to the United States. It has been listed as a threatened species in the US since 1984; the IUCN lists the species as Near Threatened. It is listed as endangered by the Missouri Department of Conservation.The Ozark cavefish is pinkish-white and reaches a maximum length of 2.0 in (5 cm). The head is flattened, and it has a slightly protruding lower jaw. The fish has no pelvic fin; the dorsal and anal fins are farther back than on most fish. It has only rudimentary eyes and no optic nerve. The Ozark cavefish lives only in caves. It has no pigmentation and has lost some unused characters. However, it is well adapted to a cave environment through well-developed sensory papillae. They feed primarily on microscopic organisms, as well as small crustaceans and salamander larvae. Their reproductive rate is low compared to most other fish.


The Percopsiformes are a small order of ray-finned fishes, comprising the trout-perch and its allies. It contains just ten extant species, grouped into seven genera and three families. Five of these genera are monotypicThey are generally small fish, ranging from 5 to 20 cm (2.0 to 7.9 in) in adult body length. They inhabit freshwater habitats in North America. They are grouped together because of technical characteristics of their internal anatomy, and the different species may appear quite different externally.

Order Percopsiformes Berg 1937Genus †Lateopisciculus Murray & Wilson1996

Genus †Percopsiformorum [Otolith]

Suborder Percopsoidei Berg 1937

Family †Libotoniidae Wilson & Williams 1992

Genus †Libotonius Wilson 1977

Family Percopsidae Regan 1911 [Percopsides Agassiz 1850; Erismatopteridae Jordan 1905]

Genus †Massamorichthys Murray 1996

Genus †Amphiplaga Cope 1877

Genus †Erismatopterus Cope 1870

Genus Percopsis Agassiz 1849 [Columbia Eigenmann & Eigenmann 1892 non Rang 1834; Columatilla Whitley 1940; Salmoperca Thompson 1850]

Suborder Aphredoderoidei Berg 1937 [Amblyopsoidei Regan 1911; Aphredoderoidea; Amblyopsoidea]

Family Aphredoderidae Bonaparte 1832 (Pirate perches)

Genus †Trichophanes Cope 1872

Genus Aphredoderus Lesueur 1833 ex Cuvier & Valenciennes 1833 [Sternotremia Nelson 1876; Asternotremia Nelson ex Jordan 1877; Scolopsis Gilliams 1824 non Cuvier 1814]

Family Amblyopsidae Bonaparte 1832 [Hypsaeidae Storer 1846] (Cavefishes)

Genus Typhlichthys Girard 1859 (Southern cavefish)

Genus Speoplatyrhinus Cooper & Kuehne 1974 (Alabama cavefish)

Genus Forbesichthys Jordan 1929 [Forbesella Jordan & Evermann 1927 non Herdman 1891 non Lacaze-Duthiers & Delage 1892] (Spring cavefish)

Genus Chologaster Agassiz 1853 (Swampfish)

Genus Amblyopsis de Kay 1842 [Troglichthys Eigenmann 1899; Poecilosomus Swainson 1839]


Sinocyclocheilus is a genus of freshwater fish in the family Cyprinidae endemic to China, where only found in Guangxi, Guizhou and Yunnan. Almost all of its species live in or around caves and most of these have adaptions typical of cavefish such as a lack of scales, lack of pigmentation and reduced eyes (some are completely blind). Several species have an unusual hunchbacked appearance and some of the cave-dwellers have a "horn" on the back (above the forehead), the function of which is unclear. In contrast, the Sinocyclocheilus species that live aboveground, as well as a few found underground, show no clear cavefish adaptions. They are relatively small fish reaching up to 23 cm (9.1 in) in length. The individual species have small ranges and populations, leading to the status of most of the evaluated species as threatened. Many species populations in the genus have yet to be evaluated.

The type species is S. tingi. The name is derived from the Latin word sino, meaning "from China", and the Greek word kyklos, meaning "circle", and the Greek word cheilos, meaning "lip".

Spring cavefish

The spring cavefish (Forbesichthys agassizii) is the only member of the genus Forbesichthys and is one of seven species in the family Amblyopsidae. This species is listed as state endangered in Missouri, but it is considered to be of least concern by the IUCN Red List due to its relatively large population size and number of subpopulations. The spring cavefish inhabits caves, springs, spring runs, and spring seeps. It is subterranean, emerging at dusk and retreating underground an hour or two before dawn. The species is located within areas of the central and southeastern United States. It stays underground after dawn, but then emerges into surface waters at dusk. They are a carnivorous fish and are well adapted to their environment. The species' breeding behavior is rarely documented. Spawning occurs underground and in darkness between January and April. The status and distribution of cave-obligate species is incomplete or lacking entirely, which makes conservation and management decisions difficult. Kentucky and Missouri are the two main states that have their agencies managing this species in some way.

Subterranean river

A subterranean river is a river that runs wholly or partly beneath the ground surface – one where the riverbed does not represent the surface of the Earth (rivers flowing in gorges are not classed as subterranean). It should also not be confused with an aquifer which may flow like a river but is contained within a permeable layer of rock or other unconsolidated materials.

Subterranean rivers may be entirely natural, flowing through cave systems. In karst topography, rivers may disappear through sinkholes, continuing underground. In some cases, they may emerge into daylight further downstream. Some fish (popularly known as cavefish) and other troglobite organisms are adapted to life in subterranean rivers and lakes. The longest subterranean river in the world is located in Mexico.Subterranean rivers can also be the result of covering over a river and/or diverting its flow into culverts, usually as part of urban development. Reversing this process is known as daylighting a stream and is a visible form of river restoration. One successful example is the Cheonggyecheon in the centre of Seoul.Examples of subterranean rivers also occur in mythology and literature.

Typhlichthys subterraneus

Typhlichthys subterraneus, the southern cavefish, is a species of cavefish in the Amblyopsidae family endemic to karst regions of the eastern United States.

Typhlogarra widdowsoni

Typhlogarra widdowsoni, the Iraq blind barb or Haditha cave garra, is a species of cyprinid fish endemic to underground water systems near Haditha in Iraq. It is the only species in its genus. This cavefish is considered critically endangered because of water extraction, which has lowered the groundwater level. Once abundant, a survey in 2012 found that it now was very rare. Another species from the same place, Caecocypris basimi, may already be extinct. The only other known cavefish in Iraq is Eidinemacheilus proudlovei.

Viviparous brotula

The viviparous brotulas form a family, the Bythitidae, of ophidiiform fishes. They are known as viviparous brotulas as they generally bear live young, although there are indications that some species (at least Didymothallus criniceps) do not. They are generally infrequently seen, somewhat tadpole-like in overall shape and mostly about 5–10 cm (2–4 in) in length, but some species grow far larger and may surpass 60 cm (2 ft).Although many live near the coast in tropical or subtropical oceans, there are also species in deep water and cold oceans, for example Bythites. Thermichthys hollisi, which lives at depths of around 2,500 m (8,200 ft), is associated with thermal vents. A few are fresh or brackish water cavefish: the Mexican blind brotula (Typhliasina pearsei), Galapagos cuskeel (Ogilbia galapagosensis), Diancistrus typhlops and some Lucifuga species.Since 2002, more than 110 new species have been added to this family.

In 2005, 26 new species were described in a single paper by Danish and German scientists and in 2007, an additional eight new genera with 20 new species were described in another paper by the same scientists.In some classifications the family Aphyonidae is placed within the Bythitidae and the tribe Dinematichthyini of the subfamily Brosmophycinae has been raised to the status of a family, the Dinematichthyidae which contains 25 genera and 114 species.The Bythitidae is divided as follows:

Subfamily Brosmophycinae

Tribe Dinematichthyini

























Tribe Brosmophycini









Subfamily Bythitinae






















Waterfall climbing cave fish

The waterfall climbing cave fish (Cryptotora thamicola), also known as the cave angel fish, is a species of troglobitic hillstream loach endemic to Thailand. It reaches a length of 2.8 centimetres (1.1 in) SL. This fish is known for its fins, which can grapple onto terrain, and its ability to climb. This fish is the only known member of its genus.

The species has been recorded from eight subterranean sites within a large karst system (Pang Mapha karst formation) in Mae Hong Son Province, Thailand. The species has an extent of occurrence of nearly 200 km2, but an area of occupancy of 6 km2; the connectivity of this karst systems is unknown, some caves are definitely connected. The species is found in eight of the caves. It has been recorded from the Susa (from where it was first collected in May 1985) and Tham Mae Lana (Borowsky and Vidthayanon 2001). It may also occur in other submerged caves in the area. However, the species has a potential threat of agricultural pollution which could impact the whole karst system, making it one location.Like other cavefish, it is depigmented and has no visible eyes. This species coexists with another hypogean (underground-living) loach, Schistura oedipus. The species is specialized for fast subterranean flowing water in the deeper zone of the cave (more than 500m from the entrance). It depends on cave microorganisms and organic matter, and is very sensitive to disturbance, water quality and hydrographic change.The species is protected under Thai law, and is found within a National Park (Pai Basin NP), but this does not necessarily protect the species as there is little restrictions on agricultural practices and regulation of tourism is needed to reduce the potential impacts to the species habitat at some sites. Human disturbance from tourism activity (some of the habitat sites are popular for caving tourism and sightseeing) may threaten the species. Agriculture and deforestation are future major threats.In 2016 it was reported that the waterfall climbing cave fish walks with a tetrapod-like diagonal-couplets lateral sequence gait, displaying a robust pelvic girdle attached to the vertebral column.

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