Taxonomy & naming
Nemacheilus terekensis was described by the Russian ichthyologist Vladimir Gratzianov in 1907, from material taken in the Terek River drainage of the northern Caucasus. It was placed, as was standard for the era, in the old broad genus Nemacheilus (then often spelled Noemacheilus), a catch-all that for decades absorbed most small Eurasian stone loaches regardless of their true relationships.
The stone-loach family Nemacheilidae has since been extensively revised, and many species once lumped into Nemacheilus have been redistributed into narrower genera — Barbatula, Oxynoemacheilus, Paracobitis, Schistura, Triplophysa and others — on the basis of osteology, fin-ray counts and, more recently, molecular data. Caucasus-region loaches from this era have in particular been folded into revisions of the western Palaearctic genus Oxynoemacheilus, and terekensis appears in that literature as a historical name tied to the Terek drainage rather than as a name in current, active use in Nemacheilus. No current source consulted here confirms a settled modern combination, so it is treated here under its original name pending a definitive Catalog of Fishes ruling; this kind of unresolved, century-old regional description is common across the stone-loach literature.
Morphology
As with the great majority of Nemacheilidae, Nemacheilus terekensis is presumed to be a small, elongate, sub-cylindrical loach with a flattened belly suited to holding position on stream substrate. Family-wide traits that almost certainly apply include a small, often barbel-fringed mouth adapted for picking food from gravel and stones, and the near-scaleless or very finely scaled skin typical of the group, which makes stone loaches broadly sensitive to medications and to sudden water-quality swings.
Detailed original-description measurements, colour pattern and meristic counts for this species were not available in the sources consulted, and no verified photograph or modern redescription could be confirmed. This is a genuinely data-sparse species: rather than guess at size, colour or fin-ray details, it is more honest to say that a firm morphological picture would require consulting Gratzianov's original 1907 description or a modern taxonomic revision of Caucasus Nemacheilidae directly.
Habitat
The type locality places Nemacheilus terekensis in the Terek River drainage, which rises in the high central Caucasus and flows northeast into the Caspian Sea through present-day Georgia, Russia and the wider Caucasus region. Like other stone and brook loaches of the family, it would be expected to live in fast-flowing, clear, cool, well-oxygenated water over gravel, stone and sand — typical highland and foothill stream habitat rather than still, warm lowland water.
No detailed modern habitat survey or population assessment for this specific name was found in the sources consulted. Its range should be understood as inferred from the type locality and from general Nemacheilidae ecology, not as a confirmed, mapped distribution.
Feeding
Nemacheilidae as a family are bottom-dwelling micro-predators, working the substrate of fast streams for small aquatic invertebrates — insect larvae, small crustaceans and other invertebrate prey — rather than grazing algae or taking food from the water column. Nemacheilus terekensis would be expected to follow this pattern, foraging over stones and gravel in flowing water.
No species-specific feeding study was found for this species, so this account follows the well-established family-level diet rather than any direct observation of terekensis itself.
Mating
No courtship or spawning behaviour has been documented for Nemacheilus terekensis in the sources consulted. Stone and brook loaches as a family are not known for elaborate courtship; where reproduction has been studied in related Nemacheilidae, pairing is brief and tied to the flow and temperature conditions of the breeding season, without the long-term pair bonds or the parental investment seen in cave-guarding or mouthbrooding fishes — neither of which applies to this family.
Breeding
Following the pattern documented for stone and brook loaches generally, Nemacheilus terekensis is presumed to be an egg-scatterer, releasing eggs over gravel or among stones in fast-flowing water with no parental care afterward. This is consistent across the Nemacheilidae and stands in clear contrast to the cave-guarding males of gobies or the mouthbrooding seen in some cichlids — neither behaviour occurs in this family.
No aquarium or captive spawning of this species has been documented, and given how little is recorded about the species even in the wild, it should be considered essentially unbred and undescribed in reproductive terms. As with most narrow-range Nemacheilidae, the honest statement is that breeding data is sparse to nonexistent.
In the aquarium
Nemacheilus terekensis has no established presence in the aquarium hobby; it was not found in the trade literature or hobbyist sources consulted, and no husbandry account exists to draw on. Were it ever encountered, general stone-loach care principles would apply — cool to moderate temperatures matching a Caucasus mountain stream rather than a warm tropical setup, strong water movement, high oxygenation, a gravel or stone substrate, and gentle handling and dosing given the family's near-scaleless, medication-sensitive skin.
This account cannot responsibly go further than that. Rather than invent tank size, feeding routine or compatibility notes for a fish with no documented aquarium history, it is more useful to flag it plainly: this is a historical, poorly known regional loach, not a hobby fish.
Conservation
Nemacheilus terekensis has not been evaluated on the IUCN Red List, and no population trend or threat assessment was found in the sources consulted. It is recorded here as Not Evaluated rather than assigned a guessed status.
As a narrow-range stream endemic of the Caucasus — a region under real pressure from water abstraction, damming and pollution across its river systems — a species like this would typically be considered at some risk simply by virtue of a restricted drainage, but without a formal assessment that remains inference rather than documented fact. Modern taxonomic and conservation review of Caucasus Nemacheilidae would be needed to say more.