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). New species are being described regularly.
Description and ecology
The body forms of 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 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 other "loaches" used to be included in this family, but nowadays are recognized as well-distinct members of the order Cypriniformes. Together with the suckers (Catostomidae), the "loaches" made up the superfamily Cobitoidea. However, the sucking loaches (Gyrinocheilidae) were easily recognizable as relatives of the suckers.
Eventually it was realized that the hillstream loaches, though more similar to the true loaches than the other two presumed Cobitoidea, are nonetheless distinct enough to be better regarded a family in their own right - Balitoridae. And as it seems the "sucking Cobitoidea" are quite distant indeed, perhaps even markedly closer to the Cyprinidae, and thus the old superfamily Catostomoidea warrants revalidation. Finally, the puzzling mountain carps were most often considered a distinct family Psilorhynchidae in recent times. But in a number of systematic schemes, they were placed in the Balitoridae (or Balitorinae, when these were included in the Cobitidae). In fact, they seem to be loachlike carps and belong in the Cyprinidae.
Use by humans
Some true loaches are popular as food fish in East Asian countries such as Japan. These are of importance in the fisheries or being raised in aquaculture. Small species may occasionally be caught for bait.
As aquarium fish
Loaches of some sort have been present in several video games:
- In the Nintendo 64 game The Legend of Zelda: Ocarina of Time, the largest fish you can catch is the "Hylian loach". The Hylian Loach appears in the fishing pond every fourth time you pay to borrow the fishing rod. It has a long low dorsal fin unlike Cobitidae and looks much like a mix between a Misgurnus true loach and the Northern Snakehead (Channa argus) which is not a loach; both these fishes are quite familiar across East Asia.
- The Hylian loach is also present in the fishing minigame in Nintendo Gamecube/Wii game The Legend of Zelda: Twilight Princess.
- Loaches also appear in the Nintendo DS game Animal Crossing: Wild World and its Wii sequel, Animal Crossing: City Folk. They are small fish found in rivers from March to May. Not rare, one specimen sells for a mere 300 bells (as much as a black bass); thus it is apparently not – as the player character wonders when catching one – a Hylian loach. The icon, though very restricted in resolution, is a correct depiction of a loach with a color pattern resembling some East Asian species of Cobitis.
"Why, they will allow us ne'er a jordan, and then we leak in your chimney; and your chamber-lie breeds fleas like a loach."
This might be a misprint, or an obsolete term for a dovecote, then as today notorious for "breeding" Ceratophyllus columbae fleas. Or it might indeed refer to the fish: the Spined Loach (Cobitis taenia), native to England, is very prolific, and the phrase can be taken to imply "...hosts fleas as abundantly as the Spiny Loach spawns".
- Kottelat, M. (2012)
- FishBase (2004), Nelson (2006)
- Nelson (2006)
- He et al. (2008)
- AS 
- Steevens (1809): p.201
- Absolute Shakespeare (AS) : King Henry IV, Part I Essay. Retrieved 2008-AUG-10.
- FishBase (2004): Family Cobitidae - Loaches. Version of 2004-NOV-22. Retrieved 2007-03-05.
- Steevens, George (1809): The Plays of William Shakespeare: With the Corrections and Illustrations of Various Commentators (Vol. 15: Hamlet, Timon of Athens). PDF fulltext at Google Books.
- He, Shunping; Gub, Xun; Mayden, Richard L.; Chen, Wei-Jen; Conway, Kevin W. & Chen, Yiyu (2008): Phylogenetic position of the enigmatic genus Psilorhynchus (Ostariophysi: Cypriniformes): Evidence from the mitochondrial genome. Mol. Phylogenet. Evol. 47: 419–425. doi:10.1016/j.ympev.2007.10.012 (HTML abstract)
- Kottelat, M. (2012): Conspectus cobitidum: an inventory of the loaches of the world (Teleostei: Cypriniformes: Cobitoidei). The Raffles Bulletin of Zoology, Suppl. No. 26: 1-199.
- Nelson, Joseph S. (2006): Fishes of the World. John Wiley & Sons, Inc. ISBN 0-471-25031-7
|Wikimedia Commons has media related to Cobitidae.|
|Wikispecies has information related to: Cobitidae|
- FishBase treatment of the family
- Loaches on The Aquarium Wiki Category of common freshwater Loaches kept in aquariums
- Loaches Online - site with comprehensive information & discussions on keeping these fish in aquaria