Taxonomy & naming
Nemacheilus marang was formally described by Renny K. Hadiaty and Maurice Kottelat in 2010, in Zootaxa 2557(1): 39–48, a paper covering several new Nemacheilus from the karst streams of eastern Borneo. The type locality is Sungai Marang itself, in the Bengalon drainage of the Sangkulirang peninsula, East Kalimantan, Indonesia — the species takes its epithet directly from that stream name.
It sits in the genus Nemacheilus, within the family Nemacheilidae, the stone or brook loaches — by species count the largest family of loaches, and one that has been heavily reshuffled by taxonomists over the past two decades as the old wastebasket genera "Nemacheilus" and "Noemacheilus" were split apart into Schistura, Triplophysa, Barbatula and others. Nemacheilus marang has remained in Nemacheilus since its description; the Catalog of Fishes is the authority for the valid combination, and no revision affecting this species is reflected in the sources consulted here. The genus name itself comes from the Greek nema (thread, filament) and cheilos (lip), a reference to the fine barbels around the mouth typical of the family.
Morphology
The original description separates Nemacheilus marang from all other Bornean congeners chiefly on colour pattern: 10 to 18 dark brown bars cross the flank from the dorsal midline down to just below the lateral line, the bars continuous across the back, regular and straight, and each narrower than the pale interspace separating it from the next. As in other members of the genus, the body is elongate and only lightly scaled — the near-scaleless skin typical of Nemacheilidae — and the mouth carries barbels used to feel out food on the stream bed.
Beyond the diagnostic banding recorded in the description, detailed morphometric and meristic data for this species have not surfaced in the sources available here, and no maximum length figure could be confirmed; this reflects how recently the species was described and how narrow its known range is, rather than any unusual biology. It is reasonable to expect a small stone loach in the same general size range as other Bornean karst-stream Nemacheilus, but that figure is not stated in the cache and is not asserted here.
Habitat
Nemacheilus marang is endemic to the karst limestone streams of the Sangkulirang peninsula in East Kalimantan, Borneo, Indonesia, and is known specifically from Sungai Marang in the Bengalon drainage. Sangkulirang is one of Southeast Asia's great limestone karst formations, riddled with caves and fed by clear, cool-to-moderate, fast-flowing streams that emerge from and disappear into the rock — habitat that has produced a number of narrowly endemic fishes found nowhere else.
As a stone loach of this setting, it lives in flowing, well-oxygenated, clear water over a hard or gravelly substrate, the same conditions its Nemacheilidae relatives depend on throughout Borneo and the wider region. No population outside this single karst catchment has been documented in the sources reviewed here, which is consistent with the genuinely narrow range typical of many Sangkulirang endemics.
Feeding
No diet study specific to Nemacheilus marang was found in the available sources. Stone loaches in this genus are generally bottom-foraging micro-predators, working the substrate of fast, clear streams for small insect larvae, worms, crustaceans and other invertebrates picked up with the help of the barbels around the mouth; there is no reason to expect this species departs from that pattern, though it has not been directly confirmed for marang itself.
In the aquarium, closely related Nemacheilus are kept on a diet of small live and frozen foods — bloodworm, Daphnia, brine shrimp — offered daily, with sinking dried foods accepted but not relied on exclusively. Given the lack of species-specific data, that same general approach is the reasonable extrapolation for this species rather than a confirmed fact.
Mating
No information on courtship, sexing or spawning behaviour specific to Nemacheilus marang appears in the sources consulted. This is unsurprising for a species known from a single, remote karst stream and described only in 2010; field observations of reproductive behaviour in such localized Nemacheilidae are rare across the genus, and none have been documented here for this species. Rather than infer a courtship pattern from more familiar loaches, the honest position is that this aspect of its biology is simply unstudied.
Breeding
As with the great majority of stone and brook loaches, Nemacheilus marang is not known to have been bred in the home aquarium, and in fact does not appear to be established in the aquarium trade at all. The general pattern across Nemacheilidae is egg-scattering over gravel or among stones in fast-flowing water, with no parental care afterward — there is no cave-guarding or mouthbrooding behaviour anywhere in this family. That mode can reasonably be expected to apply here, but it has not been directly documented for this species, and the data are sparse enough that no aquarium spawning record exists to cite.
In the aquarium
Nemacheilus marang does not appear to be an established aquarium fish; the sources available describe it purely as a taxonomic and conservation subject rather than a traded species. Where related Nemacheilus stone loaches are kept, the requirements are consistent: fast-flowing, clear, highly oxygenated water, a low tolerance for organic waste or poor water quality, and regular partial water changes — weekly changes in the 10–50% range are typical guidance across sources for this group, alongside strong filtration and a gravel or smooth-stone substrate with cover.
Being a near-scaleless loach, as the family generally is, this genus should be treated with the caution typical of Nemacheilidae around copper-based and full-strength medications. Given how little is documented about this specific species, anyone encountering it in the trade should treat it as a specialist, high-water-quality fish rather than a community tank addition, and should not assume it tolerates the warmer, stiller conditions suited to lowland species.
Conservation
Nemacheilus marang was assessed by the IUCN as Data Deficient (DD) on 24 August 2019. That status reflects its narrow known range — a single stream system in the Sangkulirang karst — and the general shortage of population, threat and life-history data for the species, rather than any confirmed stability or decline.
Sangkulirang's karst streams face pressure from limestone quarrying, logging and land-use change in eastern Borneo, threats that affect the broader community of narrowly endemic karst fishes in the region even where they have not been quantified for this particular species. With its entire known distribution confined to the Bengalon drainage, Nemacheilus marang is inherently vulnerable to any disturbance of that single catchment, and its Data Deficient status is best read as a call for further survey work rather than an assurance of safety.