Taxonomy & naming
Oxynoemacheilus marunensis was formally described by Golnaz Sayyadzadeh and Hamid Reza Esmaeili in 2020, in a paper published in the journal Zootaxa (volume 4885, issue 2). It belongs to the genus Oxynoemacheilus, one of several genera carved in recent decades out of the old, unwieldy "Nemacheilus"/"Noemacheilus" catch-all that once absorbed most Eurasian stone loaches — a reshuffling the Catalog of Fishes, the standing authority for valid fish names, continues to track as new species are described and molecular data reassigns others.
The species epithet marunensis refers to its type locality, the Marun River, a tributary of the Jarrahi River in Iran's Persian Gulf drainage. In the original description, the authors separated it from the morphologically similar Oxynoemacheilus karunensis using a combination of body-proportion measurements — notably a longer pelvic-to-anal-fin distance — and DNA barcoding, which showed roughly 6% divergence in the COI gene between the two, a gap consistent with distinct species in this group. As with many recently split Oxynoemacheilus, expect the genus limits around it to keep shifting as more of the region's streams are surveyed.
Morphology
Like other members of Nemacheilidae, Oxynoemacheilus marunensis is a small, elongate, cylindrical fish built for holding position on the bottom of fast water rather than for open swimming. The original description highlights two bold black spots at the base of the caudal fin as a distinguishing mark, set against the slender, mottled body typical of the genus. As in related stone loaches, it likely carries the small erectile spine beneath the eye characteristic of the wider Cobitoidea group, along with the tiny, deeply embedded scales — bordering on scaleless skin — that make this whole family sensitive to medication.
No maximum length, weight, or detailed morphometric range beyond the diagnostic proportions used to separate it from O. karunensis has been published for this species. Data on its full adult size and growth is sparse, which is typical for narrow-range stream endemics named from a handful of museum specimens rather than a long-studied population.
Habitat
The type locality is the Marun River, a tributary of the Jarrahi River in the Persian Gulf basin of southwestern Iran — placing this species firmly within the arid-region freshwater fauna of the Iranian plateau and Zagros foothills, a zone known for a high density of narrow-range endemic fishes shaped by isolated river systems. Stone loaches of this genus typically inhabit cool-to-warm, clear, well-oxygenated, flowing water over gravel, sand or rocky substrate, and there is no reason from the description to expect otherwise here.
No published data give the specific temperature, pH or seasonal flow regime of the Marun River at the collection site. Given the genus and the semi-arid Persian Gulf drainage it occupies, a moderately warm, well-oxygenated, flowing stream environment is the reasonable expectation, but precise water-chemistry data for this species has not been documented.
Feeding
No diet study exists for Oxynoemacheilus marunensis specifically. Stone loaches in this genus and family are overwhelmingly bottom-foraging micro-predators, picking small invertebrates — aquatic insect larvae, worms and tiny crustaceans — from among gravel and stones in flowing water, and this species almost certainly follows the same pattern.
In the absence of species-specific data, any aquarium diet should follow the established genus norm: small sinking live, frozen and prepared foods that reach the substrate, since fast-water stone loaches are adapted to hunting along the bottom rather than taking food from midwater or the surface.
Mating
No information on sexual dimorphism, courtship or spawning behaviour has been published for this species. Stone loaches of this type are not known to be sexually dimorphic in any dramatic way, and the original taxonomic description — focused on distinguishing the species from its close relative — does not address reproductive biology at all.
Breeding
There is no record of Oxynoemacheilus marunensis being bred, or even kept, in the aquarium. Stone and brook loaches in Nemacheilidae are, as a rule, egg-scatterers that release eggs over gravel in flowing water with no parental care, and are rarely bred in captivity even where they do reach the hobby. Given that this species was described only in 2020 from a single Iranian drainage and appears to be essentially absent from the aquarium trade, its breeding biology should be considered undocumented rather than assumed.
In the aquarium
Oxynoemacheilus marunensis is not an established aquarium fish; there is no evidence it is traded or kept by hobbyists, and this profile should be read as a natural-history record of a recently described, narrow-range endemic rather than a care guide. Any keeper attempting to house a stone loach from this genus should default to the broader Nemacheilidae pattern: cool-to-moderate, clear, well-oxygenated, flowing water over a fine gravel or sand substrate, since these fish are adapted to fast streams and do poorly in warm, still water. As with all near-scaleless loaches, caution with copper-based and full-strength medications would apply if the species were ever kept.
Conservation
Oxynoemacheilus marunensis has not been evaluated by the IUCN Red List; it is treated here as Not Evaluated rather than assigned a guessed status. Described only in 2020 and known from the Marun River, a single tributary system within the Jarrahi/Persian Gulf basin, it fits the profile of many recently described stone loaches: a narrow-range endemic about which too little population or threat data exists to support a formal assessment. Iranian and broader Middle Eastern freshwater fish diversity faces documented pressures from water extraction, damming and drought across the region's river systems, but no species-specific conservation data has been published for this fish.