Taxonomy & naming
Oxynoemacheilus karunensis was formally described by Jörg Freyhof in 2016 in Zootaxa, as part of a wave of revisionary work that has split the old, broadly-defined genera Nemacheilus and Noemacheilus into a mosaic of narrower genera across the Middle East, Anatolia and Central Asia — Oxynoemacheilus, Paracobitis, Schistura, Turcinoemacheilus and others among them. The species belongs to the O. persa species group within Oxynoemacheilus, a genus that as currently understood spans roughly 70 species from Albania in the west to central Iran in the east.
The type locality is the Karun and Jarrahi (also called Marun or Maroon) Rivers, part of the Persian Gulf basin in southwestern Iran. The species epithet karunensis simply names the Karun, Iran's longest river and the core of its range. As with most recent Oxynoemacheilus descriptions, the Catalog of Fishes is the authority for the valid combination, and no synonymy or reclassification affecting this name is known at this time.
Morphology
Freyhof separated O. karunensis from its congeners chiefly on a suite of fine anatomical characters: males show a distinctive suborbital groove, and the species has a deeply emarginate to forked caudal fin, a feature that sets it apart from several similar Persian Gulf basin Oxynoemacheilus. Like other members of the genus it is a slender, elongate, small-bodied loach; congeners in the persa group and nearby genera typically run 3–3.5 in total length, and there is no evidence O. karunensis departs greatly from that pattern, though a specific maximum length has not been published for this species.
As in other Nemacheilidae, the skin carries no true suborbital spine of the botiid kind — that structure belongs to the unrelated family Botiidae. Nemacheilids instead rely on small size, cryptic colouration and a flattened, current-hugging body shape to hold position on stony river beds. The skin is thin and the scales, where present, are minute and deeply embedded, leaving the fish effectively naked-skinned and, as in other loaches, correspondingly sensitive to strong medication.
Habitat
This species is endemic to Iran, known from the Karun and Jarrahi river systems draining into the Persian Gulf. The Karun is Iran's longest river at roughly 590 mi with the country's largest drainage basin, and the basin as a whole is unusually rich in endemic fish, supporting well over a dozen species found nowhere else. The habitat recorded for O. karunensis is a fast, shallow, bedrock-and-gravel stream reach: depths of roughly 4–6.5 in, channel widths around 7–8 ft, a moderate slope of 1.6–2.2%, and swift water velocities of 1–13 ft/s over a coarse bedrock substrate.
That is classic stone-loach country — clear, cool-to-mild, well-oxygenated, fast-flowing water rather than the warm, still, tannin-stained water associated with many tropical Southeast Asian loaches. Nothing in the available literature suggests this species tolerates brackish water or still, warm conditions; it should be treated as a cool, flowing-water specialist unless further study says otherwise.
Feeding
No dedicated dietary study of O. karunensis has been published. By analogy with its close relatives in Oxynoemacheilus, which forage on the stream bed for small invertebrates, insect larvae, crustaceans and organic detritus — locating food partly by touch with the barbels around the mouth — it is reasonable to expect a similar micro-predatory, benthic diet, but this should be read as an informed inference from the genus rather than a confirmed fact for this species.
In a hypothetical aquarium setting, a loach of this type would be expected to take small sinking live and frozen foods (bloodworm, daphnia, chopped invertebrates) readily, and to show little interest in floating flake, consistent with the feeding pattern seen across small benthic Nemacheilidae.
Mating
No description of courtship or spawning behaviour has been published for O. karunensis specifically. Congeners in Oxynoemacheilus are reported to spawn in spring to early summer, triggered by rising water levels, with males showing mild territoriality around the breeding period. Whether O. karunensis follows this same seasonal cue in its Karun and Jarrahi river habitat has not been documented, and no sexual dimorphism has been described for the species beyond the suborbital groove noted in males as a taxonomic character.
Breeding
There is no record of this species being bred in captivity, and it is not established in the aquarium trade at all. Based on the breeding pattern documented across Oxynoemacheilus and the wider Nemacheilidae, the expected mode is an egg-scatterer: eggs released over gravel and stones in fast-flowing water, with no parental care of eggs or fry. Data for this specific species is sparse to the point of being essentially absent beyond the original taxonomic description, and nothing should be assumed about its breeding behaviour beyond that general family pattern.
In the aquarium
Oxynoemacheilus karunensis is not a hobby fish — there is no evidence it is traded, and this account should be read as a taxonomic and ecological profile of a data-sparse stream endemic rather than a care guide drawn from aquarium experience. If it were ever kept, everything about its known habitat argues for a cool-to-mild, fast-flowing, well-oxygenated stream setup with a hard, bedrock-and-gravel substrate and strong water movement, rather than the warm still water suited to many popular tropical loaches.
As with all nemacheilids, the near-scaleless skin means any such fish would need careful, reduced-strength medication and would likely be an early indicator of deteriorating water quality or disease in a mixed system. None of this is trade-tested; it is a projection from the species' known river ecology and its family's general biology, offered honestly as inference rather than established fact.
Conservation
Oxynoemacheilus karunensis has not been formally assessed by the IUCN Red List and carries no conservation category; it is recorded here as Not Evaluated rather than assigned a guessed status. Described only in 2016, it is a narrow-range endemic restricted to the Karun and Jarrahi river systems of southwestern Iran, a basin that already supports a large share of Iran's endemic freshwater fish fauna and is subject to the pressures common across the region — water abstraction, damming and habitat modification in a heavily-used river system.
There is no evidence of an aquarium trade in this species, so collection for the hobby is not a documented threat. Its conservation profile is best summarized honestly: a recently-described, single-basin endemic with no red-list assessment and no population data, the pattern typical of small, poorly-studied stone loaches across the Middle East.