Taxonomy & naming
The species was first described in 1922 by Ernst Ahl. Confusingly, the same name and river system were revisited decades later: Coad & Nalbant, in 2005, described a monotypic genus Ilamnemacheilus for a single specimen from the same drainage, initially treated as a separate taxon before subsequent molecular and morphological work folded it back in and the population was transferred to the genus Oxynoemacheilus, where FishBase currently lists it as Oxynoemacheilus longipinnis. This kind of repeated reshuffling is typical of Nemacheilidae, a family the Catalog of Fishes revises frequently as old catch-all genera such as Nemacheilus and Noemacheilus are split into Schistura, Triplophysa, Barbatula, Oxynoemacheilus and others on a river-by-river basis.
This article keeps the genus Nemacheilus per the site's working taxonomy, but readers researching the species further should expect to find current literature under Oxynoemacheilus longipinnis. Re-description work distinguishes it from close relatives by the suborbital groove present in males, dorsal-fin ray count, body colouration, upper-lip shape and caudal-fin form.
Morphology
Nemacheilus longipinnis is a very small, slender stone loach, reaching only about 1.5 in in standard length — near the small end even for a family built of small fish. Like other nemacheilids it has a cylindrical, elongate body, a ventrally flattened head suited to hugging the streambed, barbels around a small underslung mouth, and reduced, deeply embedded scales that leave the skin close to naked — a trait that matters for disease sensitivity in any nemacheilid kept in captivity.
Detailed colouration and fin-ray counts beyond the material used to separate it from related Iranian stream loaches have not been compiled in the sources available here; this is a data-sparse point pending fuller redescription.
Habitat
The species is endemic to the Meymeh River, a tributary within the Tigris-Euphrates drainage in Ilam Province, western Iran, with its type locality about 11 mi west of Dehloran. It has been recorded from moderately fast-flowing water through to nearly standing pools within the same system — clean springs, streams and river reaches over mud or gravel substrate, in a subtropical freshwater setting.
All known records come from the type locality and nearby sites within the same drainage, making this a genuine single-river endemic. No population has been documented outside the Meymeh system, consistent with the broader Nemacheilidae pattern of narrow, stream-restricted ranges across South, Central and West Asia.
Feeding
FishBase records the species as omnivorous, with a trophic level of about 2.9 — consistent with the typical nemacheilid pattern of a benthic micro-predator picking small invertebrates, insect larvae and other food items off the bottom of clear, flowing water, supplemented by some plant or detrital material. No dedicated dietary study of this species has been located; the omnivore classification is the extent of what the cache supports.
Mating
No spawning behaviour, seasonality or courtship has been documented for this species in the sources available. Data is sparse for a narrow single-river endemic that has not been studied in the aquarium trade or bred in captivity, and nothing here should be inferred beyond what related stone loaches typically do.
Breeding
Nothing specific to Nemacheilus longipinnis has been published on reproduction. Going by the general pattern for stone and brook loaches (Nemacheilidae), the expected mode is an egg-scatterer that releases eggs over gravel or among stones in flowing water with no parental care — but this is inference from the family, not a documented observation for this species, and it has not been bred in the aquarium. Given the total absence of trade or hobby records, this should be read as an honest gap rather than a confirmed account.
In the aquarium
Nemacheilus longipinnis has no known presence in the aquarium trade, and no aquarium-care source could be located for it. It is not a fish a keeper is likely to encounter for sale. For context, nemacheilid stone loaches in general are near-scaleless and sensitive to copper and full-strength medications, and do best in cool-to-moderate, clear, well-oxygenated, flowing water over sand or fine gravel — but none of that has been verified specifically for this species, and no husbandry recommendation can responsibly be made beyond noting the family pattern.
Conservation
Nemacheilus longipinnis has not been formally assessed on the IUCN Red List and is listed here as Not Evaluated. As a species known only from a single river drainage in Ilam Province, Iran, it fits the profile of many narrow-range nemacheilid endemics that carry real conservation interest — vulnerability to water abstraction, damming or pollution within one small catchment — but without a formal assessment no status or threat level can be asserted. It is not known to be part of the aquarium trade, so collection pressure is not a documented concern for this species.