Taxonomy & naming
Oxynoemacheilus zarzianus was formally described by Jörg Freyhof and Matthias Geiger in 2017 in the journal Zootaxa, from material collected in the Lesser Zab River drainage of Iraqi Kurdistan. It belongs to the family Nemacheilidae — the stone loaches or brook loaches — the largest of the loach families and one that has been repeatedly reshuffled as older catch-all genera such as Nemacheilus and Noemacheilus were broken apart; Oxynoemacheilus is one of the genera that absorbed many Middle Eastern and Anatolian species in that process, and the Catalog of Fishes governs the currently valid combination used here.
The species epithet zarzianus references the Zarzian, a late Palaeolithic/Mesolithic archaeological culture of Iraqi Kurdistan, tying the name to the region of the type locality rather than to any feature of the fish itself. It is diagnosed from congeners by a combination of characters given in the original description: a slightly emarginate caudal fin, the absence of a suborbital groove in males, a complete lateral line, the posterior process of the bony air-bladder capsule directed posteriorly, scales present on the flank and posterior back, short barbels, and a deep caudal peduncle.
Morphology
As a member of Oxynoemacheilus, O. zarzianus is a slender, elongate loach with a rounded head, short barbels and the small, deeply embedded scales typical of the family — the skin reads as effectively naked, a point that matters for husbandry. FishBase gives a maximum size of about 3 in standard length, making it a small representative of the genus. The original description notes a deep caudal peduncle and a slightly emarginate (shallowly notched) caudal fin, along with a complete lateral line running the length of the body; dorsal and anal fin ray counts are modest (8 dorsal, 5 anal rays), consistent with other Oxynoemacheilus.
Males lack a suborbital groove, one of the characters used to separate this species from close relatives — a reminder that, unlike the botiid loaches, Nemacheilidae species do not carry an erectile suborbital spine; identification in this family instead rests on fine anatomical and meristic detail rather than obvious external armament. Colouration is not detailed in the sources available here, and beyond the diagnostic features in the type description the species' external appearance is not well documented outside the specialist literature.
Habitat
Oxynoemacheilus zarzianus is known only from the Lesser Zab River drainage in Iraqi Kurdistan, part of the wider Tigris system. It occupies the cold, spring-fed, fast-flowing streams typical of its genus, which across the Eastern Mediterranean and Middle East specialises in headwater and high-altitude stream habitats — clear water running over gravel and stone substrates, often at elevation, where oxygen levels are high and flow is constant.
This is a cool-water, running-water fish, not a warm still-water species: Oxynoemacheilus as a genus is built around cold, spring-fed streams, and there is nothing in the record for this species to suggest otherwise. Individuals reportedly shelter under stones and among gravel during the day, consistent with the genus-wide pattern of daytime cover-seeking followed by more active nocturnal foraging.
Feeding
FishBase places Oxynoemacheilus zarzianus at a trophic level of about 2.8, indicating a diet weighted toward algae and detritus alongside some small invertebrate prey — broadly herbivorous/detritivorous rather than strictly predatory. This fits the genus-wide pattern for Oxynoemacheilus, whose members forage benthically over stones and gravel for a mix of algae, detritus and small benthic invertebrates, using their barbels to locate food on and among the substrate.
No aquarium feeding record exists for this species specifically. Going by its trophic position and its relatives, a diet of sinking algae-based wafers and small invertebrate foods (fine frozen or live foods) alongside natural biofilm grazing would be the appropriate approach, rather than treating it as a pure carnivore.
Mating
No courtship or spawning behaviour has been recorded for Oxynoemacheilus zarzianus in the sources available. Nemacheilid stone and brook loaches as a group are egg-scatterers with no pair-bonding or nest-building behaviour on record; spawning in the wild is understood to take place over gravel and stones in fast-flowing water, timed to seasonal flow conditions in the way many stream-dwelling loaches are. Nothing more specific can be said for this species without over-reaching beyond what has actually been documented.
Breeding
There is no record of Oxynoemacheilus zarzianus being bred in captivity. Consistent with other stone and brook loaches, the expected mode is egg-scattering over gravel or among stones in fast, oxygenated water, with no parental care of eggs or fry once they are released. This is a genuinely data-sparse species — described only in 2017 from a single river drainage — and it has no history in the aquarium trade or hobbyist breeding record to draw on.
Given that pattern, the honest position is that O. zarzianus should be treated as effectively unbred in captivity, with any future spawning likely to require the cool, fast-flowing, high-oxygen conditions of its native headwater habitat rather than a standard tropical community setup.
In the aquarium
Oxynoemacheilus zarzianus is not an established aquarium fish; it has no meaningful presence in the hobby and no dedicated care literature exists for it. Anyone encountering it would need to extrapolate from the genus: a cool-to-cool-temperate, fast-flowing, high-oxygen stream setup with a gravel or stone substrate, strong filtration and current, and stable, clean water, rather than the warm, calm conditions suited to many tropical loaches.
As with other nemacheilids, the near-scaleless skin implied by its small, deeply embedded scales means any medication should be approached cautiously — full-strength treatments and copper-based products are best avoided or used at reduced dose with scaleless fish generally. Given how little is documented about this species' tolerances, keeping it would currently be an exercise in careful replication of cold, running headwater-stream conditions rather than following any established protocol.
Conservation
Oxynoemacheilus zarzianus has not been assessed on the IUCN Red List and is recorded here as Not Evaluated rather than assigned a guessed status. It is known only from the Lesser Zab River drainage in Iraqi Kurdistan, a single-catchment range that — as with many recently described Middle Eastern stream loaches — leaves it with no formal conservation status but a narrow known distribution that would typically warrant assessment.
No trade or collection pressure is documented for this species; it is not known to be part of the aquarium trade. Its status is best understood as data-sparse rather than either secure or threatened, and any future conservation picture would depend on water use, damming or pollution pressures within the Lesser Zab drainage specifically.