Taxonomy & naming
Oxynoemacheilus hazarensis was described in 2017 by Jörg Freyhof and Müfit Özuluğ in Zootaxa, as part of a revision that also clarified the status of the closely related Oxynoemacheilus euphraticus. It sits in the family Nemacheilidae, the stone or brook loaches, a group that was carved out of the old catch-all genera Nemacheilus and Noemacheilus over the past few decades and has since been split further into Oxynoemacheilus, Schistura, Triplophysa, Barbatula, Paracobitis and others as the Catalog of Fishes — the standing authority for valid fish names — has worked through the group's tangled history.
The species name hazarensis refers to its type locality, Lake Hazar, and marks it as a lake-restricted endemic in a family whose members are overwhelmingly stream fish. The description was built on comparison with O. euphraticus, the geographically nearest congener in the wider Tigris–Euphrates system, and the differences between the two — detailed in the original paper — are what justify treating the Lake Hazar population as its own species rather than a population of its neighbour.
Morphology
As a member of Nemacheilidae, Oxynoemacheilus hazarensis is a small, elongate, bottom-hugging loach built for holding position in current — though its own habitat, a rift lake rather than a stream, is somewhat unusual for the family. The original description separates it from Oxynoemacheilus euphraticus on a set of fine anatomical characters: a slightly emarginate (shallowly forked) caudal fin, the absence of a suborbital groove in males, an incomplete lateral line, no scales on the back and flanks anterior to the anus, a maxillary barbel that reaches beyond the middle of the eye, a small incision in the upper lip, and a mottled rather than banded flank pattern.
Congeners in the euphraticus group run roughly 1.5–3 in standard length, which gives a working sense of scale for this species, though no separate maximum-length figure for O. hazarensis specifically has been published. Like other nemacheilids it is presumed near-scaleless over much of the body — consistent with the description's note on scale loss anterior to the anus — a detail that matters for handling and medication rather than everyday appearance. Beyond the diagnostic features above, detailed colouration and proportions are not well documented outside the original taxonomic paper.
Habitat
Oxynoemacheilus hazarensis is endemic to Lake Hazar (also written Hazar Gölü), a lake in the upper Tigris drainage of eastern Turkey, at roughly 1,814 ft altitude. Lake Hazar is a rift lake with brackish-alkaline chemistry unusual for a freshwater loach habitat: published water-chemistry surveys record a mean pH around 9.1 — very hard, strongly alkaline water — alongside good (first-class) dissolved oxygen and oligotrophic (nutrient-poor) conditions.
The lake's high altitude points to a cool climate rather than the warm lowland rivers most stone loaches occupy elsewhere in Eurasia; a lake at this elevation likely runs cool for much of the year, plausibly in the neighbourhood of 39–59 °F during summer, though no direct year-round temperature record for the species has been published. This combination — a single high-altitude, hard-alkaline rift lake — makes O. hazarensis geographically and ecologically distinct from the flowing, generally softer streams typical of the genus, and it is precisely this narrow, unusual range that leaves so much about its ecology undocumented.
Feeding
No feeding study specific to Oxynoemacheilus hazarensis has been published, so its diet must be inferred from the family. Nemacheilid stone loaches are bottom-oriented micro-predators, working the substrate for small invertebrates — insect larvae, small crustaceans and other invertebrate prey — rather than grazing algae or taking much plant matter.
Given the oligotrophic, first-class-oxygen chemistry of its home lake, O. hazarensis most likely forages over sediment and rock in similarly clean, invertebrate-poor-but-present conditions typical of a nutrient-poor rift lake. In the absence of direct data, any aquarium approach should follow the family default: small sinking live, frozen or prepared foods offered at the substrate, rather than assuming it will take flake from midwater.
Mating
Nothing specific to Oxynoemacheilus hazarensis has been published on courtship, spawning triggers or sexual dimorphism — a direct consequence of its narrow endemic range and the fact that it is known essentially only from its 2017 description. The type description does not report reliable external sex differences for the species, and no aquarium or field observations of spawning behaviour appear in the literature.
For the wider stone-and-brook-loach group, spawning is typically an unremarkable, cue-driven affair tied to rising water and warming temperatures rather than any elaborate courtship display. Whether Lake Hazar's population follows a comparable seasonal pattern, given its lake rather than stream setting, is simply not documented.
Breeding
There is no record of Oxynoemacheilus hazarensis being bred in captivity. Stone and brook loaches of this family are, as a rule, egg-scatterers: ripe adults release eggs over gravel or among stones in flowing water, with no parental care given afterward. That is the honest baseline to assume here, but it should be stated plainly as an inference from the family rather than a confirmed fact for this species.
Given that O. hazarensis is a narrow single-lake endemic with no aquarium trade history, essentially no hobbyist has ever kept — let alone spawned — this fish. Any captive breeding would be a first for the species and would need to start from close observation of its actual behaviour rather than assumptions carried over from stream-dwelling relatives.
In the aquarium
Oxynoemacheilus hazarensis has no known aquarium history: it is not established in the hobby, and no husbandry account has been published. Anyone attempting to keep it would be working from family-level principles rather than species-specific guidance, and should treat every parameter as provisional.
As a nemacheilid, likely near-scaleless, it should be treated with the caution the family generally demands: avoid copper-based medications and full-strength treatments, since scaleless and near-scaleless loaches absorb them readily and are often the first fish in a tank to show stress or disease. Given the lake's cool, hard, strongly alkaline, well-oxygenated, oligotrophic chemistry, a keeper attempting this species should lean toward cooler, well-oxygenated, hard-alkaline water with a clean substrate — the opposite setup from the warm, soft, acidic water suited to many tropical stream loaches — rather than defaulting to generic warm-tropical parameters. Given the total absence of trade or husbandry data, this section is necessarily conservative.
Conservation
Oxynoemacheilus hazarensis has not been assessed on the IUCN Red List and carries no conservation category; it is recorded here as Not Evaluated rather than assigned a guessed status. It was only described in 2017, and as a single-lake endemic restricted to Lake Hazar in the upper Tigris drainage, it is exactly the kind of narrow-range species that would be a strong candidate for future assessment.
No population trend, threat analysis or trade data have been published for this species. Its entire known range is one lake basin, which by definition makes it vulnerable to any large-scale change in that single water body — water abstraction, pollution, or the introduction of non-native species — even though no specific threat has been documented. There is no evidence this species is currently part of the aquarium trade.