Loaches are fish of the superfamily Cobitoidea. They are
freshwater
Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...
,
benthic
The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...
(bottom-dwelling)
fish
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
found in rivers and creeks throughout
Eurasia
Eurasia (, ) is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Japanese archipelago a ...
and
northern Africa
North Africa, or Northern Africa is a region encompassing the northern portion of the African continent. There is no singularly accepted scope for the region, and it is sometimes defined as stretching from the Atlantic shores of Mauritania in t ...
.
Loaches are among the most diverse groups of fish; the 1249 known
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
of Cobitoidea comprise about 107
genera
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...
divided among 9
families
Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideal ...
.
Etymology
The name Cobitoidea comes from the type genus, ''Cobitis'', described by
Carl Linnaeus
Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...
in his landmark 1758
10th edition of ''Systema Naturae''. However, its origin predates modern zoological nomenclature and derives from a term used by
Aristotle
Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of phil ...
to refer to "small fishes that bury... like the
gudgeon
A gudgeon is a socket-like, cylindrical (i.e., ''female'') fitting attached to one component to enable a pivoting or hinging connection to a second component. The second component carries a pintle fitting, the male counterpart to the gudgeon, ...
."
Description
Loaches display a wide variety of morphologies, making the group difficult to characterize as a whole using external traits. They range in adult length from the 23 mm (1 in) miniature eel-loach, ''
Pangio longimanus
''Pangio'' is a genus of small Asian freshwater fish in the true loach family Cobitidae. In earlier taxonomic schemes it was known as ''Acanthophthalmus''. The "kuhli loach" is well-known in the aquarium trade and commonly identified as ''P. ku ...
'', to the 50 cm (20 in) imperial flower loach, ''
Leptobotia elongata
''Leptobotia elongata'', the imperial flower loach, elongate loach or royal clown loach, is a species of botiid fish found in flowing water in the upper and middle Yangtze basin in China.SeriouslyFishLeptobotia elongata Retrieved 10 March 2017. ...
'', with the latter weighing up to 3 kg (6.6 lbs). Most loaches are small, narrow-bodied and elongate, with minute
cycloid
In geometry, a cycloid is the curve traced by a point on a circle as it rolls along a straight line without slipping. A cycloid is a specific form of trochoid and is an example of a roulette, a curve generated by a curve rolling on another curve ...
scales that are often embedded under the skin, patterns of brown-to-black pigment along the dorsal surface and sides, and three or more pairs of whisker-like
barbels
In fish anatomy and turtle anatomy, a barbel is a slender, whiskerlike sensory organ near the mouth. Fish that have barbels include the catfish, the carp, the goatfish, the hagfish, the sturgeon, the zebrafish, the black dragonfish and some s ...
at the mouth.
The type species of the family Cobitidae, ''
Cobitis taenia
The spined loach (''Cobitis taenia'') is a common freshwater fish in Europe. It is sometimes known as spotted weather loach, not to be confused with the "typical" weather loaches of the genus ''Misgurnus''. This is the type species of the spiny l ...
'', has a body shape and pigment pattern typical of Cobitoidea. However, many loaches are eel-like or conversely, quite stout-bodied; some
balitorids have large, visible scales.
Loaches in the families
Cobitidae
Cobitidae, also known as the True loaches, is a family of Old World freshwater fish. They occur throughout Eurasia and in Morocco, and inhabit riverine ecosystems. Today, most "loaches" are placed in other families (see below). The family includ ...
,
Botiidae
Botiidae is a family of cypriniform ray-finned fishes from South, Southeast, and East Asia. Until recently they were placed in the true loach family Cobitidae, until Maurice Kottelat revised the loaches and re-elevated this taxon to family rank ...
, and
Serpenticobitidae possess a bifid, protrusible spine below the eye, or in the case of the genus ''
Acantopsis
''Acantopsis'' is a genus of freshwater fishes, commonly known as horseface loaches or banana-root fishes, in the family Cobitidae.Boyd, D. A., Nithirojpakdee, P., Deein, G., Vidthayanon, C., Grudpan, C., Tangjitjaroen, W., Pfeiffer, J. M., Randa ...
'', between the eye and the tip of the snout.
Taxonomy
Classification
Cobitoidea is a superfamily within the order
Cypriniformes
Cypriniformes is an order of ray-finned fish, including the carps, minnows, loaches, and relatives. Cypriniformes is an Order within the Superorder Ostariophysi consisting of "Carp-like" Ostariophysins. This order contains 11-12 families, ...
, one of the most diverse groups of vertebrates. The order is commonly known as "minnows, carps, loaches, and relatives," and it includes the suckers (
Catostomidae
The Catostomidae are the suckers of the order Cypriniformes, with about 78 species in this family of freshwater fishes. The Catostomidae are almost exclusively native to North America. The only exceptions are ''Catostomus catostomus,'' found in ...
) and algae eaters (
Gyrinocheilidae
''Gyrinocheilus'' is the single genus in the family Gyrinocheilidae, a family of small Southeast Asian cypriniform fishes that live in fast-flowing freshwater mountain streams. The species in this genus are commonly called "algae eaters." They ho ...
). Fishes of the latter family, which contains only a single genus ''
Gyrinocheilus
''Gyrinocheilus'' is the single genus in the family Gyrinocheilidae, a family of small Southeast Asian cypriniform fishes that live in fast-flowing freshwater mountain streams. The species in this genus are commonly called "algae eaters." They h ...
'', are sometimes referred to as sucking loaches. It is uncertain if Gyrinocheilidae, or a clade containing both Gyrinocheilidae and Catostomidae, is sister to Cobitoidea.
History of classification
At the turn of the 20th century only two families of loaches had been described, and of these only Cobitidae was widely recognized by taxonomists. In the early 1900s, the American
ichthyologist
Ichthyology is the branch of zoology devoted to the study of fish, including bony fish ( Osteichthyes), cartilaginous fish (Chondrichthyes), and jawless fish (Agnatha). According to FishBase, 33,400 species of fish had been described as of Octobe ...
Fowler and the Indian ichthyologist
Hora recognized what would come to be known as Balitoridae and Gastromyzontidae. Nemachelidae, and later Botiidae, were described as subfamilies of Cobitidae until their elevation to family status in 2002. Owing to shared morphological characteristics (see osteology, below) the relationship of the botiid and cobitid loaches was particularly difficult to resolve until the advent of
molecular phylogenetics
Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...
. Three of the nine families, containing only two or three species apiece, were recognized within the last ten years.
Phylogeny
Reproduction of molecular phylogeny of Cobitoidea from Bohlen & Šlechtová, 2009, with common names following Eschmeyer's Catalog of Fishes.
Osteology
Among loaches, the majority of known morphological
synapomorphies
In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...
(shared characters derived from a common ancestor) are
osteological
Osteology () is the scientific study of bones, practised by osteologists. A subdiscipline of anatomy, anthropology, and paleontology, osteology is the detailed study of the structure of bones, skeletal elements, teeth, microbone morphology, func ...
. In particular, modifications to the ethmoid and surrounding bones within the neurocranium unite Cobitoidea, in addition to certain lateral-line canal ossifications.
An erectile suborbital spine, a modification of the lateral ethmoid, was formerly thought to represent a synapomorphy between Cobitidae and Botiidae. It is now considered a
pleisiomorphy of Cobitoidea, a character shared by the common ancestor but lost in most loach lineages. The suborbital spine is also retained in the
serpent loaches, Serpenticobitidae.
Habitat and distribution
Loaches are found in a wide variety of habitats throughout Europe, northern Africa, and central and Southeast Asia. Most families occur predominantly in rocky mountain streams at high elevations, but almost all have lowland representatives as well.
Many species of Cobitidae burrow in the sand and inhabit riverbeds in broad, flat terrain. At least three families contain blind,
troglomorphic
Troglomorphism is the morphological adaptation of an animal to living in the constant darkness of caves, characterised by features such as loss of pigment, reduced eyesight or blindness, and frequently with attenuated bodies and/or appendages. The ...
species adapted to life in caves.
Relationship with humans
Some loaches are important food fish, especially in East and Southeast Asia where they are a common sight in markets.
Loaches are popular in the aquarium trade. Some of the most well-known examples are the
clown loach
The clown loach (''Chromobotia macracanthus''), or tiger botia, is a tropical freshwater fish belonging to the botiid loach family. It is the sole member of the genus ''Chromobotia''. It originates in inland waters in Indonesia on the islands ...
(''Chromobotia macracanthus''), the
kuhli loach
The kuhli loach (''Pangio kuhlii'') is a small eel-like freshwater fish belonging to the loach family ( Cobitidae). They originate from Indonesia and the Malay Peninsula. This snake-like creature is very slender and nocturnal. In an aquarium, t ...
(''Pangio kuhlii''), and the
dwarf chain loach (''Ambastaia sidthimunki''). Botiid and gastromyzontid loaches also occasionally make their way into the trade.
Although loaches have a strictly Old World native distribution, the
oriental weatherfish, ''Misgurnus anguillicaudatus'', (also known as the dojo loach) has been introduced in parts of the United States.
References
{{Taxonbar , from=Q2246081
Cypriniformes