Belongs within: Cypriniformes.
The Cobitidae, loaches, are small, slender fishes found in Eurasia and Africa that bear three to six pairs of barbels around the mouth and have the gas bladder encapsulated in bone.
Loaches
Published 10 July 2013
The spined loaches of the Cobitidae are a family of small freshwater fishes found across Eurasia, with a single species (Cobitis maroccana) making it to the northern tip of Africa. A recent catalogue of the family by Kottelat (2012) recognised twenty-one genera in the families, though phylogenetic studies suggest that some reshuffling may be necessary: the Chinese Paramisgurnus dabryanus, for instance, may be nested within the genus Misgurnus, while the Sino-Japanese genus Niwaella may be a polyphyletic grouping of elongate species adapted to fast-flowing mountain streams (Šlechtová et al. 2008).
As a whole, loaches are more or less worm-like fishes that feed by benthic scavenging. Most species are small, less than ten centimetres long, though the Thai Acantopsis spectabilis gets up to around 15 centimetres (Kottelat 2012), and the weather fish Misgurnus anguillicaudatus reaches about 25 cm. Phylogenetically, the family was divided by Šlechtová et al. (2007) into two groups, a ‘northern clade’ containing the northern Eurasian species in the genera Cobitis, Misgurnus and related taxa, and a paraphyletic ‘southern group’ containing the remaining southern and south-east Asian species. The ranges of the northern and southern subdivisions overlap in northern Vietnem, but otherwise the two groups are geographically disjunct. A potential morphological synapomorphy of the northern clade is a horizontal ossified structure, called the ‘scale of Canestrini’, on the second ray of the male’s pectoral fin, but if so this character has been lost in some subtaxa such as the western Eurasian genus Sabanejewia.
One interesting detail about the northern spined loaches is the existence in various localities of natural polyploid populations: such polyploids have been identified among European Cobitis species, and in the Japanese Misgurnus anguillicaudatus. These mostly triploid (sometimes tetraploid) populations of loaches reproduce clonally, but are always found in association with a sexually-reproducing diploid population. This is because the parthenogenetic females are what is referred to as ‘sperm parasites’. The parthenogenetic females still mate with sexual males, not to be fertilised but in order that the act of mating will stimulate egg production. In external appearance, these polyploids are generally indistinguishable from their co-existing diploid associates. European polyploid Cobitis are believed to have arisen through hybridisation between closely related sexual species, possibly through male sperm fertilising an unreduced diploid egg.
Oh yes, and there are cave-dwelling loaches out there: two Chinese species, placed in the genus Protocobitis, are blind species collected from groundwater. How they relate to the above-ground species remains unknown.
Systematics of Cobitidae
Cobitidae [Cobitididae]
|--Acanthopsis choirorhynchus (Bleeker 1854) [=Cobitis choirorhynchus]K55b
|--Iksookimia Nalbant 1993P07
|--Oreonectes Günther 1858TP86
| `--O. anophthalmus Zheng 1981TP86
|--MisgurnusSE08
| |--M. anguillicaudatusHM01
| `--M. fossilis (Linnaeus 1758)SE08
|--Acanthophtalmus kuhliiK55b
| |--A. k. kuhliiK55b
| `--A. k. sumatranus Fraser-Brunner 1940K55b
|--Sabanejewia Vladykov 1929P07
| |--S. aurata (de Filippi 1863)SE08
| `--S. romanica (Băcescu 1943)SE08
|--Lepidocephalichthys thermalisRM72
`--Cobitis Linnaeus 1758L58
|--C. barbatula Linnaeus 1758L58
|--C. biwaeT90
|--C. centrochir Agassiz 1835P93
|--C. elongatoides Băcescu & Maier 1969SE08
|--C. fossilis Linnaeus 1758L58
|--C. melanoleuca Nichols 1925 (see below for synonymy)P07
|--C. olivai Nalbant, Holčik & Pivnička 1970 [=C. granoei olivai, C. melanoleuca olivai]P07
|--C. paludicaKKV03
|--C. striataSM03 [=C. taenia striataT90]
|--C. taenia Linnaeus 1758 [=Acanthopsis taenia]K55a
| |--C. t. taeniaK55a
| |--C. t. haasi Klausewitz 1955K55a
| `--C. t. maroccanaK55a
`--C. takatsuensisT90
Cobitis melanoleuca Nichols 1925 [=C. taenia melanoleuca; incl. C. granoei Rendahl 1935, C. taenia granoei, C. taenia sibirica Gladkov 1935]P07
*Type species of generic name indicated
References
[HM01] Harris, P. M., & R. L. Mayden. 2001. Phylogenetic relationships of major clades of Catostomidae (Teleostei: Cypriniformes) as inferred from mitochondrial SSU and LSU rDNA sequences. Molecular Phylogenetics and Evolution 20 (2): 225–237.
[K55a] Klausewitz, W. 1955a. Cobitis taenia haasi, eine iberische Unterart der Dorngrundel, (Pisces, Cobitidae). Seenckenbergiana Biologica 36: 41–43.
[K55b] Klausewitz, W. 1955b. See- und Süßwasserfische von Sumatra und Java. Senckenbergiana Biologica 36 (5–6): 309–323.
[KKV03] Kontula, T., S. V. Kirilchik & R. Väinölä. 2003. Endemic diversification of the monophyletic cottoid fish species flock in Lake Baikal explored with mtDNA sequencing. Molecular Phylogenetics and Evolution 27: 143–155.
Kottelat, M. 2012. Conspectus cobitidum: an inventory of the loaches of the world (Teleostei: Cypriniformes: Cobitoidei). Raffles Bulletin of Zoology, Supplement 26: 1–199.
[L58] Linnaeus, C. 1758. Systema Naturae per Regna Tria Naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata. Laurentii Salvii: Holmiae.
[P93] Patterson, C. 1993. Osteichthyes: Teleostei. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 621–656. Chapman & Hall: London.
[P07] Prokofiev, A. M. 2007. Cobitis olivai Nalbant, Holčik & Pivnička 1970, a valid species of spined loaches from Mongolia: redescription and comparison with C. melanoleuca Nichols 1925 (Osteichthyes, Cypriniformes, Cobitidae). Senckenbergiana Biologica 87 (1): 111–124.
[RM72] Rajagopal, K. V., & V. Muddanna. 1972. Two unique methods of fishing for cobitids in the Tungabhadra River. Journal of the Bombay Natural History Society 69 (2): 429–432.
[SM03] Saitoh, K., M. Miya, J. G. Inoue, N. B. Ishiguro & M. Nishida. 2003. Mitochondrial genomics of ostariophysan fishes: perspectives on phylogeny and biogeography. Journal of Molecular Evolution 56: 464–472.
[SE08] Sevcsik, A., & T. Erös. 2008. A revised catalogue of freshwater fishes of Hungary and the neighbouring countries in the Hungarian Natural History Museum (Pisces). Annales Historico-Naturales Musei Nationalis Hungarici 100: 331–383.
Šlechtová, V., J. Bohlen & A. Perdices. 2008. Molecular phylogeny of the freshwater fish family Cobitidae (Cypriniformes: Teleostei): delimitation of genera, mitochondrial introgression and evolution of sexual dimorphism. Molecular Phylogenetics and Evolution 47: 812–831.
[T90] Taguchi, S. 1990. Nihon no Sakana. Kogakukan: Tokyo.
[TP86] Thinès, G., & G. Proudlove. 1986. Pisces. In: Botosaneanu, L. (ed.) Stygofauna Mundi: A Faunistic, Distributional, and Ecological Synthesis of the World Fauna inhabiting Subterranean Waters (including the Marine Interstitial) pp. 709–733. E. J. Brill/Dr W. Backhuys: Leiden.