Taxonomy & naming
Cobitis nigrolinea was described by Chen & Chen in 2017 from the Xin'anjiang River (Xin'an River) in Anhui Province, China, and published in the taxonomic literature that year alongside other new Chinese Cobitis species. It was originally placed in the genus Niwaella, as Niwaella nigrolinea, a genus historically used for some East Asian spined loaches; molecular phylogenetic work, including mitochondrial genome studies, has since treated Niwaella nigrolinea as a junior synonym, with the species now carrying the valid combination Cobitis nigrolinea. This article follows that current placement.
The species belongs to the family Cobitidae, the true or spined loaches, which also contains the temperate European and Asian Cobitis and Sabanejewia species and the dojo or weather loach Misgurnus. As a 2017 description with a very restricted known range, it has not accumulated the kind of long taxonomic history seen in older, wider-ranging Cobitis — its record is short, recent, and still being clarified by ongoing molecular work.
Morphology
Cobitis nigrolinea is a small, extremely elongated loach, reaching a maximum of about 2.5 in standard length. Its most conspicuous feature, and the one that gives it its name, is a solid black stripe running from the occiput (back of the head) all the way to the caudal fin along the top of the back, set off by short, dense vertical bars along the dorsolateral surface. Like other Cobitidae it carries the family's diagnostic feature, a thick, curved, erectile suborbital spine tucked in a groove beneath the eye — a defensive structure typical of the group and usable to distinguish it from superficially similar loaches.
Other distinguishing features include a split lower lip and mandible, underdeveloped mental lobes, and a notably long processus latero-caudalis and caudal peduncle, details that separate it from related Cobitis species at close examination. No external sexual dimorphism has been reported for this species; as with many small, recently described Cobitis, the sexes have not been documented as visibly distinct.
Habitat
The species is known from the Xin'anjiang River (Xin'an River) drainage in Anhui Province, in subtropical eastern China. It is a benthic freshwater fish of swift-moving mountain streams, living over pebble and boulder substrates in clear, fast-flowing water — the classic habitat of a stream-dwelling Cobitis rather than a still-water pond species.
This subtropical mountain-stream setting places Cobitis nigrolinea in cooler, well-oxygenated, current-swept water rather than warm, still tropical conditions. Its close relatives among the temperate Eurasian Cobitis and the dojo Misgurnus are coldwater fish that tolerate unheated conditions; while data specific to this species' thermal tolerance has not been published, its subtropical mountain-stream origin suggests cool-to-moderate water rather than either full coldwater or warm tropical extremes.
Feeding
No diet-specific data has been published for Cobitis nigrolinea. Based on the well-documented feeding ecology of its Cobitidae relatives, it is reasonable to infer a benthic omnivore that sifts a soft or fine substrate for small invertebrates — worms, insect larvae, small crustaceans — along with algae and detritus, in the manner typical of spined and pond loaches. This inference should be treated as a general family pattern, not a confirmed fact for this specific species.
In the absence of aquarium-specific feeding records, any care approach should default to offering a varied diet of small sinking foods over a soft substrate, consistent with how related stream-dwelling Cobitis are fed, while acknowledging that this species' actual dietary needs remain undocumented.
Mating
No mating or spawning behaviour has been documented for Cobitis nigrolinea in the available literature. The species was described from wild-collected specimens for taxonomic purposes, and no aquarium or field breeding observations appear to exist.
Among the wider genus Cobitis, courtship and spawning in the temperate species that have been studied — including pond-kept populations of European Cobitis — typically involves scattering of adhesive eggs among vegetation, often in spring. Whether Cobitis nigrolinea follows this same seasonal pattern in its native subtropical mountain streams has not been recorded.
Breeding
There is no published record of Cobitis nigrolinea being bred, in the wild or in captivity. As a very recently described species restricted to a single Chinese river system, it has essentially no aquarium history to draw breeding data from.
Within the family Cobitidae, the temperate spined and pond loaches — including several Cobitis and Sabanejewia species and the dojo/weather loach Misgurnus — are the ones most often pond- or tank-spawned, typically scattering adhesive eggs among plants with no parental care. The tropical Cobitidae, by contrast, are generally not bred at home. Cobitis nigrolinea's subtropical, poorly known status places it outside either well-documented case: the honest statement is that it has never been recorded breeding in captivity, and any egg-scattering, no-parental-care mode should be understood as inferred from its family, not observed in this species.
In the aquarium
Cobitis nigrolinea has no established aquarium-keeping history — it is not known to be present in the hobby, and no care reports, tank parameters, or long-term husbandry accounts have been published. Anyone encountering it would be working from the general principles that apply to small stream-dwelling Cobitidae rather than from species-specific guidance.
Those general principles are worth stating cautiously: like other true loaches it is likely near-scaleless and correspondingly sensitive to copper and full-strength medications, and as a fast-water, pebble-bottom species it would be expected to want cool-to-moderate, well-oxygenated, current-swept water rather than a warm, still tropical setup. Given the total absence of documented care data, this species should be treated as essentially unavailable and unproven in the aquarium rather than recommended for the hobby.
Conservation
Cobitis nigrolinea has not been evaluated by the IUCN Red List. Given its very recent description (2017) and its apparent restriction to the Xin'anjiang River drainage in Anhui Province, China, no conservation status has been assigned, and none should be inferred.
A species known from a single river system is inherently vulnerable to localized pressures — pollution, damming, or habitat alteration — but without a formal assessment or population data, no claim can be made here beyond noting the restricted known range and the absence of any evaluation to date.