The body forms of the Cobitidae tend to be
vermiform – worm-shaped, long and thin. Most true loaches do not have true
scales, and like many other
Cypriniformes or
catfishes, they have
barbels at their mouths (usually three to six 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. 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 "weather fishes" or "weather loaches". Some Cobitidae have been
introduced to foreign lands, where they may pose problems to local wildlife as
invasive species. 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. ==Systematics==