Taxonomy & naming
Nemacheilus bertini was described by P. W. Fang in 1941. It sits in the genus Nemacheilus, within the family Nemacheilidae — the stone or brook loaches, by far the largest and most species-rich family of true loaches. Nemacheilidae has been heavily revised over the past few decades: the old, broad genera Nemacheilus and Noemacheilus once absorbed hundreds of species that have since been redistributed into Schistura, Triplophysa, Barbatula, Oxynoemacheilus, Paracobitis and other genera as the group's internal relationships were worked out. Nemacheilus bertini has not been swept into that reshuffling in the sources consulted here, and it is treated under its original combination.
No dedicated FishBase, IUCN or hobbyist profile for this species turned up in research for this article, which is itself informative: it signals a narrow-range or poorly-collected species rather than an error, a pattern that is common across Nemacheilidae, where many species are known from a single river system or even a single type locality and have never been re-examined since their original description.
Morphology
Detailed morphological data for Nemacheilus bertini — body length, fin ray counts, colour pattern, barbel arrangement — was not located in the sources checked, and none is invented here. What can be said comes from its placement in Nemacheilidae: stone and brook loaches are typically small, elongate, cylindrical-to-slightly-compressed fish with a flattened underside suited to holding position on the streambed, several pairs of barbels around the mouth for detecting food by touch, and reduced or embedded scales that leave the skin close to the surface. Many members of the genus and family carry the small erectile suborbital spine characteristic of loaches more broadly, tucked in a groove below the eye.
Until primary literature or a verified photograph of Nemacheilus bertini can be reviewed, its exact size and markings should be treated as unconfirmed rather than assumed from relatives.
Habitat
No specific locality, river system or water-chemistry data for Nemacheilus bertini was found in the sources checked for this profile. As a member of Nemacheilidae, it almost certainly comes from the cool-to-warm, clear, fast-flowing, well-oxygenated streams that define the family's habitat across South, Southeast and East Asia — the group's classic niche is riffles and runs over sand, gravel and stone rather than still or heavily vegetated water. But without a confirmed type locality or subsequent collection record in hand, this profile does not assign the species to a specific country or drainage.
Given the described authority and genus, a Chinese or nearby East/Southeast Asian origin is plausible on taxonomic grounds alone, but that is not the same as a documented distribution, and none is claimed here.
Feeding
No feeding observations specific to Nemacheilus bertini were found. Stone and brook loaches as a group are bold benthic micro-predators, working the bottom of fast streams for small invertebrates — insect larvae, small crustaceans and other invertebrate prey — rather than grazing algae or biofilm in the manner of hillstream loaches. If ever kept, this species would be expected to follow that pattern and take small live, frozen or sinking foods offered near the substrate, but this is an inference from the family, not a documented fact about the species.
Mating
No information on courtship, sexing or spawning behaviour for Nemacheilus bertini was found in the sources checked. Stone loaches in general show little obvious external dimorphism outside the breeding season, and almost nothing has been documented about pairing or courtship for the great majority of Nemacheilidae species, which are simply too poorly studied or too rarely encountered — in the wild or in captivity — for behavioural observations to exist.
Breeding
There is no record of Nemacheilus bertini being bred in captivity, and this appears to be true of the great majority of Nemacheilidae. Where breeding has been documented in the family at all, stone and brook loaches are egg-scatterers that release eggs over gravel and among stones in flowing water, with no parental care afterward. On present evidence this species should be assumed to follow that pattern, but the honest summary is that its reproduction has not been documented and it is not known to have been bred in the aquarium.
In the aquarium
Nemacheilus bertini is not established in the aquarium trade, and no husbandry record for it was found. It is not offered for sale under this name in the hobby, and any specimen encountered would most likely arrive as an unidentified or misidentified stone loach mixed in with shipments of similar-looking Nemacheilidae from Asia. Keepers who do encounter fish sold simply as "Nemacheilus sp." should not assume they have this species without expert verification — species-level identification within this family is difficult even for specialists.
As general guidance drawn from the family rather than from this species specifically, stone and brook loaches do best in cool-to-moderate, clean, well-oxygenated, flowing water over sand or fine gravel, and — like other loaches — are largely scaleless and correspondingly sensitive to copper-based and full-strength medications.
Conservation
Nemacheilus bertini has not been assessed on the IUCN Red List and is recorded here as Not Evaluated rather than assigned a guessed status. Many Nemacheilidae species restricted to a single stream or small drainage are inherently vulnerable to habitat degradation, damming and pollution even where no formal assessment exists, but without a documented range or population record for this species, no specific conservation claim can be made beyond noting the general pressures facing small-range Asian stream fishes.