Taxonomy & naming
Koreocobitis rotundicaudata was described by Wakiya and Mori in 1929, originally placed in the wide-ranging genus Cobitis like most spined loaches of its era. It was later moved into Koreocobitis, a small genus erected for the spined loaches endemic to the Korean Peninsula, where it now sits alongside its close relative K. naktongensis. GBIF confirms the authority as (Wakiya & Mori, 1929) and lists the species under taxon ID 2367903.
The genus name Koreocobitis simply combines "Korea" with Cobitis, the type genus of the family — a straightforward geographic label for a lineage found only on the peninsula. The family Cobitidae, the true spined and pond loaches, is the group that gives the whole loach lineage its old vernacular name, on account of the erectile spine each member carries below the eye. A mitogenomic phylogeny (Springer, 2011) supports the split between K. rotundicaudata of the Han River and K. naktongensis of the neighboring Nakdong River drainage, treating their separation as a case of geographic isolation driving speciation between adjacent river systems.
Morphology
This is a modestly sized loach: FishBase records a maximum length of about 6.5 in total length, on the larger side for a stream-dwelling spined loach but still a fish that fits comfortably in a modest aquarium. The body carries dense, dark spotting over an orange-toned ground colour, a pattern distinctive enough among Korean loaches to aid field identification. As in the rest of Cobitidae, the skin is set with tiny, deeply embedded scales that leave it functionally naked — a point that matters for handling and any future medication.
The species epithet rotundicaudata is diagnostic in itself: from Latin rotundus ("round, circular") and caudata ("tailed"), it names the rounded caudal fin that distinguishes this species from close relatives with more truncate or emarginate tails. Like other members of the family, it carries the erectile suborbital spine tucked in a groove beneath the eye — the anatomical feature that gives spined loaches their name and that can flick out defensively when the fish is threatened or handled.
Habitat
Koreocobitis rotundicaudata is endemic to the Han River drainage of South Korea and found nowhere else. It lives over pebbly bottoms in slow-flowing, shallow streams, the kind of clear, well-oxygenated water typical of Korean lowland and foothill drainages. Loaches Online describes it living among dense aquatic vegetation within these streams, with a preference for burrowing into sandy patches of substrate when available.
This is unambiguously a temperate, coolwater species, not a tropical one. Reported aquarium temperatures run 64–72 °F (64–72 °F) with a pH of 7.0–7.7 and only moderate hardness — conditions that call for an unheated or lightly cooled setup rather than a standard tropical community tank. Good filtration and some water movement, paired with subdued lighting, reflect the clear, flowing streams it comes from.
Feeding
In the wild this species forages over the streambed for aquatic insects, the mainstay of its natural diet according to FishBase. Like other bottom-dwelling Cobitidae it is a sand- and gravel-sifting benthic feeder, working over pebbly substrate to pick out small invertebrates rather than actively hunting in open water.
In the aquarium it takes proprietary sinking foods readily, supplemented with live or frozen foods such as bloodworm or small crustaceans to mirror its natural insect-heavy diet. A soft or fine-gravel substrate area lets it forage and burrow as it would in a Korean stream; a bare-bottomed tank denies it this natural feeding behaviour.
Mating
No detailed account of courtship or spawning behaviour for Koreocobitis rotundicaudata appears in the sources consulted — data here is sparse. Loaches Online notes plainly that breeding has not been documented in captivity, and the species is rare enough in the hobby, appearing mostly as accidental imports, that few keepers have had the opportunity to observe its reproductive behaviour at all.
What can be said follows from its family and its temperate range: Cobitidae spined loaches typically pair or gather to scatter adhesive eggs among vegetation, with spawning cued by seasonal warming in spring. Whether this species follows that pattern closely has not been documented, and no aquarium account confirms it.
Breeding
As a member of the spined and pond loach family, K. rotundicaudata would be expected to scatter adhesive eggs among plants in spring, in the general pattern seen across Cobitidae — with no parental care afterward. Several temperate relatives in this family, including various Cobitis, Sabanejewia, and the dojo or weather loach Misgurnus, have been pond- or tank-spawned by hobbyists and researchers taking advantage of their coldwater tolerance.
For this species specifically, though, no captive spawning has been documented. Loaches Online is explicit that breeding is undocumented in the hobby, and the species' rarity in the trade — it turns up mostly as an accidental import rather than a deliberately kept fish — means there has been little opportunity for anyone to try. The honest picture is that K. rotundicaudata has essentially never been bred in the aquarium.
In the aquarium
Koreocobitis rotundicaudata is rare in the aquarium trade, showing up mostly by accident rather than as a deliberately imported or farmed species. Anyone who does keep it should treat it as a coolwater fish first: the reported range of 64–72 °F means an unheated or lightly cooled setup suits it far better than a warm tropical community tank, and it should not be mixed with fish that need genuinely warm water.
A setup with good filtration, gentle to moderate flow, subdued lighting, dense planting, and a patch of sandy substrate for burrowing comes closest to its native pebbly Han River streams. Like other Cobitidae it is essentially scaleless, so it will absorb medications readily and should be treated cautiously and at reduced strength if disease treatment becomes necessary. At up to about 6.5 in, it needs more swimming room than the smallest loaches, and its true requirements in a home aquarium remain thinly documented given how seldom it is kept.
Conservation
Koreocobitis rotundicaudata has not been evaluated on the IUCN Red List, so it carries no formal conservation category — Not Evaluated is the honest, current status rather than a guess. As a single-river endemic restricted entirely to the Han River drainage of South Korea, it is inherently vulnerable to any degradation of that one system, from pollution to damming to habitat alteration, even though no formal assessment quantifies the risk.
The species is not a target of the aquarium trade in any organized way; the individuals that reach hobbyists arrive as incidental imports rather than deliberate collection or captive breeding. Its conservation story is really the conservation story of the Han River itself — a narrow geographic range that leaves this small, distinctive loach with nowhere else to go if its home waters decline.