Taxonomy & naming
Schistura nasifilis was described by the French ichthyologist Jacques Pellegrin in 1936, originally as a variety of another species — Nemachilus spilopterus var. nasifilis — rather than as a full species in its own right. The genus Nemachilus (also spelled Noemacheilus) was a broad, now-defunct catch-all for stone loaches across Asia, and much of it has since been split among several genera, with many of its former members reassigned to Schistura. The Catalog of Fishes, the standing authority for valid fish names, now lists the species as Schistura nasifilis (Pellegrin, 1936), the parentheses signalling that it was not described in its current genus.
The species belongs to Nemacheilidae, the stone and brook loach family, the largest of the loach lineages and one built almost entirely of small, hardy, often narrowly distributed stream fish. Schistura is itself an enormous genus within that family, with new species still being described regularly from Southeast Asian headwaters — a reminder that the group's true diversity is still being mapped.
Morphology
Schistura nasifilis is a small loach, with FishBase reporting a maximum length of 4 in standard length from the type material. Pellegrin's original description highlighted an elongated body and, notably, strong tooth-like processes on both jaws, along with an anterior nostril drawn out into a pointed tube — a feature reflected in the species name. Like other members of its genus it would be expected to carry the erectile suborbital spine typical of the broader Cobitoidea superfamily and the near-scaleless, delicate skin common to stone loaches, though the original description does not detail every character.
Beyond the type series, no substantial morphological data has been published. The species has not been rediscovered since its 1936 collection, so there is no modern material to expand on Pellegrin's account, and later authors have had to work from the same specimens he examined.
Habitat
The type locality is the rivers Ko and Tan (Song Ko and Song Tan) in Annam, central Vietnam — upland freshwater streams, consistent with the benthopelagic, high-altitude habitat typical of the genus. Stone loaches in Schistura generally hold to cool, clear, fast-flowing, well-oxygenated water over gravel and stone, and there is no reason from the available record to expect S. nasifilis differed from that pattern.
No temperature or water-chemistry data has been recorded for the species specifically. Targeted survey efforts in 2000 and 2002 failed to relocate it in its known range, and the IUCN treats it as extremely rare or possibly already lost from at least part of its historical habitat — a sobering illustration of how a single-locality stream endemic can vanish from view without anyone noticing at the time.
Feeding
No diet has been documented for Schistura nasifilis itself. Stone loaches in this genus are, as a rule, bold benthic micro-predators that pick small invertebrates — insect larvae, small crustaceans and other stream fauna — off the substrate of fast, clear water, and there is no indication this species departed from that pattern.
This is a genus-level inference rather than a species-specific finding, offered cautiously given how little direct data exists. Without any modern specimens or field observations, nothing more precise can honestly be said.
Mating
The only reproductive information on record comes from a single 2.5 in specimen in the type series, whose ovaries contained eggs of roughly 0.5 in in diameter — a scrap of data suggesting the species matures at a modest size, but far too little to describe courtship, timing or spawning behaviour.
No sexual dimorphism has been described for the species, and with no living population known to science since 1936, there has been no opportunity to observe mating behaviour directly. Any account of its reproductive biology beyond that one data point would be guesswork.
Breeding
Schistura nasifilis has never been kept or bred in the aquarium hobby — there is no trade record for it at all. Based on the reproductive biology of stone and brook loaches generally, the expected mode would be an egg-scatterer releasing eggs over gravel and among stones in fast-flowing water, with no parental care, but this is inferred from the genus rather than observed in this species.
As with most Nemacheilidae, captive breeding is essentially unknown even for species that do reach hobbyist tanks, and this one has never reached the trade in the first place. The honest summary is that breeding data is sparse to nonexistent.
In the aquarium
Schistura nasifilis is not an aquarium fish. No trade presence has been documented for the species, and given that it has not been collected since 1936 and could not be relocated by field surveys in 2000 and 2002, it is not realistically obtainable. This entry exists as a conservation and taxonomic record rather than a keeping guide.
Genus-level care notes for Schistura are worth stating for context only: these are cool-to-cold, fast-flowing, highly oxygenated stream fish, intolerant of warm, still water, and — like most scaleless loaches — sensitive to copper and full-strength medications. None of that has been verified for this particular species.
Conservation
The IUCN Red List assesses Schistura nasifilis as Critically Endangered (2022 assessment). The justification is stark: the species is known only from its original 1936 collection in the Song Ko and Song Tan rivers of Annam, Vietnam, and despite dedicated searches in 2000 and 2002 it has not been found since — raising the real possibility that it has already been lost, whether to habitat change, pollution or some other pressure affecting Vietnamese upland streams over the intervening decades.
There is no aquarium trade pressure on this species; whatever threatens it operates entirely within its native range. Its story stands as a caution for the many other narrow-range Schistura and Nemacheilidae species scattered across Southeast Asian headwaters — small, easily overlooked fish restricted to single streams, for which the gap between "still there" and "quietly gone" can close without anyone noticing.