Taxonomy & naming
Pieter Bleeker described Cobitis schlegeli in 1863, but modern loach taxonomy treats the name as a nomen oblitum — a technically valid but long-unused name that has been superseded in practice by Cobitis biwae, described by Jordan & Snyder in 1901 and confirmed in the Catalog of Fishes as the name under which this Japanese spined loach is generally recognised. This entry keeps the genus Cobitis as directed, in the family Cobitidae — the true spined and pond loaches, the group whose members carry the erectile suborbital spine.
The genus Cobitis is a large, mostly Eurasian assemblage of small, elongate, sand-dwelling loaches that has been repeatedly revised as regional species complexes are resolved with modern taxonomic tools. Cobitis schlegeli / biwae sits within that complex as a Japanese endemic, distinct from the many Cobitis species described from mainland Europe and continental Asia.
Morphology
This is a small, slender, laterally compressed loach reaching about 4.5 in in standard length, patterned with the dark blotches and stripes typical of Cobitis — camouflage that suits a fish that spends much of its life pressed against sand and gravel. Like every member of the family Cobitidae, it carries a small, sharp, erectile spine hidden in a groove beneath each eye, which it can flick out when handled or threatened; this suborbital spine is the family's defining feature and the reason the group is called the spined loaches.
The skin is covered in tiny, deeply embedded scales rather than large overlapping ones, leaving it functionally near-scaleless — a trait shared across the loach families that makes this fish, like its relatives, more exposed to skin damage and more sensitive to certain medications than scaled fish.
Habitat
Cobitis schlegeli / biwae is endemic to Japan, found on the islands of Honshu, Shikoku and Kyushu. It is a benthopelagic river fish, living over sandy and gravelly substrates in flowing, temperate freshwater rather than still ponds or lakes.
Crucially, this is a coldwater species, not a tropical one: reported temperatures in the wild and in cultivation run around 54–72 °F. That places it alongside other temperate members of the genus, such as the European spined loach Cobitis taenia, which lives in a similar cool range, rather than with the warm-water tropical Cobitidae such as Acantopsis or Lepidocephalichthys.
Feeding
As a sand-dwelling Cobitis, this species is a benthic omnivore that sifts through soft substrate for small invertebrates — worms, insect larvae and other tiny bottom-dwelling prey — along with some detritus. The cache does not document a detailed dietary breakdown for this exact species, but its biology fits the pattern typical of the genus and family: a fish that needs a soft, sand-based substrate to forage naturally rather than a hard, sterile bottom.
In cultivation and the aquarium trade, sinking foods that reach the substrate are the practical way to feed a bottom-oriented sifter like this, mirroring how it would take worms and small invertebrates off and out of the sand in the wild.
Mating
Sources describe the species as oviparous with distinct pairing during the breeding season — that is, courting fish form recognisable pairs rather than spawning as an anonymous group scatter. Beyond that pairing behaviour, the cache does not provide further detail on courtship displays or seasonal triggers for this specific species, and the safer course is to note that data as sparse rather than to guess.
What can be said with confidence is that, as a temperate Cobitis, its reproductive cycle is keyed to a cooler seasonal cycle than the tropical loaches in this family — consistent with spawning as water warms in spring, the general pattern in temperate spined loaches.
Breeding
This is a spined and pond loach (Cobitidae), and like other Cobitis it scatters adhesive eggs among plants, typically as water temperatures rise in spring. Several temperate members of the genus — including this species' close relatives — plus the coldwater dojo/weather loach Misgurnus have been pond- or tank-spawned by breeders and researchers, unlike the tropical Cobitidae (the horseface loach Acantopsis, and Lepidocephalichthys), which are rarely bred under any conditions.
For Cobitis schlegeli / biwae specifically, the cache notes it is oviparous with distinct pairing and is commercially cultured in Japan, which points to a species that can be propagated under controlled, cool-water conditions by dedicated breeders and fisheries operations. There is no parental care after spawning: eggs are scattered and left, and any survival depends on cover and water quality rather than guarding adults. This is not a home-aquarium staple to breed casually, but it sits on the more tractable, temperate end of the loach breeding spectrum rather than the essentially unbred tropical botiids and hillstream genera.
In the aquarium
The single most important care point for this species is temperature: it is a coldwater fish, thriving around 54–72 °F, and does not need — and should not be kept in — a heated tropical community tank. An unheated aquarium or an outdoor pond that stays within a temperate range suits it far better than warm tropical water.
Like other true loaches it is near-scaleless, so standard full-strength medications and copper-based treatments should be used with caution and often at reduced dose. Give it a soft sand or fine gravel substrate to sift through, since a hard or sharp-edged bottom is uncomfortable and unnatural for a burrowing, sand-associated loach. Being commercially cultured in Japan, this is a species with an established captive supply chain rather than one solely dependent on wild collection, though hobbyist availability outside Japan is limited and specialist. As with the wider family, it is a bottom-oriented, retiring fish that appreciates cover and the company of its own kind rather than being kept as a lone specimen.
Conservation
Cobitis schlegeli has not been assessed on the IUCN Red List, so it is recorded here as Not Evaluated rather than assigned a status the source material does not support. Its close ally and current valid name, Cobitis biwae, is a range-restricted Japanese endemic found only on Honshu, Shikoku and Kyushu, which is the kind of narrow, single-country distribution that often makes small stream and river loaches vulnerable to local habitat pressures even without a formal assessment.
The species is commercially cultured in Japan, which suggests at least part of any trade or food-fish demand is met through cultivation rather than solely wild harvest. No further conservation detail is available in the cache, so this entry deliberately says no more than the sources support.