Cobitidae is the family of the true loaches, which are 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). But more than 100 species remain in the Cobitidae, while the number of genera has almost doubled to nearly 30 in the past few years[when?] due to new discoveries and divisions of older genera. New species are being described regularly.
The body forms of Cobitidae range from vermiform – worm-shaped, long and thin – to fusiform – spindle-shaped, cylindrical and tapering toward the ends. Most true loaches do not have true scales, and like many other Cypriniformes or catfishes, they have barbels at their mouths (usually 3-6 pairs). Some other traits typically found in this family are a small bottom-facing mouth suited to their scavenging benthic lifestyle, an erectile spine below the eye, and a single row of pharyngeal (throat) teeth.
True loaches are mostly scavengers and are omnivorous, usually not very picky about their food. They may eat aquatic crustaceans, insects and other small invertebrates as well as scraps of organic detritus. Many live in eutrophic waters of generally poor quality and feed on tubifex worms and similar benthos associated with such habitat. Some of these loaches have adapted to low oxygen levels in warm, muddy rivers or dirty ponds by being able to gulp up atmospheric oxygen from the air. Some species, particularly from the genera Cobitis and especially Misgurnus are sensitive to changing air pressure. They change their behavior accordingly, and as these changes in activity are usually followed by a change in weather, they are commonly known as "weatherfishes" or "weather loaches".
Because of their scavenging nature and their ability to adapt to many freshwater ecosystems, some Cobitidae have been introduced to foreign lands where they may pose problems to local wildlife as invasive species[verification needed]. Other true loaches, many of them migratory fish, have been seriously affected by habitat destruction, chemical pollution and damming, and are considered threatened species today. Some migratory species are popular aquarium fish and since they are very hard to raise in captivity, overfishing has seriously depleted once-common stocks in several cases.
The Botiinae are the smaller subfamily, with 7 genera generally accepted today. Some of these are quite speciose however. The Cobitinae contain the remaining genera, but while a few make up the bulk of the remaining diversity of Cobitidae, many are very small or monotypic.
Many of the more brightly-colored species, in particular Botiinae, are popular with freshwater aquarists and are therefore of importance in the aquarium trade. The more colorful tropical species that are kept as pets are mainly South Asian and Southeast Asian Botiinae. Cobitidae often encountered in aquarium trade include:
Clown Loach, Chromobotia macracanthus
Dojo Loach, Misgurnus anguillicaudatus
Horseface Loach, Acantopsis choirorhynchus
Skunk Loach, Yasuhikotakia morleti
Kuhli Loach, Pangio kuhlii
Yoyo Loach, Botia almorhae
Zebra Loach, Botia striata
Bengal Loach, Botia dario
Burmese Border loach, Botia kubotai