Taxonomy & naming
The species was described by Bănărescu & Nalbant in 1978 as Nemacheilus eregliensis, with its type locality in the Lake Tuz basin of central Anatolia — the name recalls Ereğli, a town near the basin's streams. Nemacheilus was for decades a wastebasket genus for Eurasian stone loaches, and molecular and morphological revisions of the western Palaearctic fauna have since split it apart; the Catalog of Fishes, the authority followed here, now places this fish in Oxynoemacheilus, the genus erected for the Anatolian, Caucasian and Middle Eastern stone loaches. The combination Nemacheilus eregliensis is an obsolete synonym and should not be used.
A further population from the Lake Beyşehir basin, once described separately as Oxynoemacheilus atili, is now treated as a synonym of O. eregliensis, widening the species' known range within central Anatolia's closed drainage basins. The genus Oxynoemacheilus itself sits in the family Nemacheilidae, the stone or brook loaches, the largest and most species-rich family in the loach superfamily Cobitoidea.
Morphology
Oxynoemacheilus eregliensis is a small, elongate loach with an oval cross-section to the body, reaching a recorded maximum of around 4 in total length in males and unsexed individuals — most wild specimens measured in surveys run well under that, with standard lengths reported from under 1 in up to roughly the maximum. The colour pattern is a dark-brown mottling over a paler ground, broken into irregular blotches along the flank, a fairly typical camouflage pattern for a fish that spends its life pressed against gravel and sand.
As in other nemacheilids, the skin carries only small, deeply embedded scales or none at all over much of the body, leaving it functionally naked and, as with all scaleless loaches, sensitive to copper and full-strength medications. Many Oxynoemacheilus species carry a small erectile spine near the eye typical of the broader loach group, though the available sources do not describe this feature in detail for O. eregliensis specifically, and no further anatomical claim is made here beyond what is documented.
Habitat
This species is a demersal freshwater fish of subtropical Anatolia, endemic to the closed Lake Tuz basin in central Turkey, with a further population in the Lake Beyşehir basin. It has been recorded from streams and springs feeding the basin — the Melendiz Stream among them — over substrates of gravel, sand and mud, in slowly to moderately flowing water rather than the torrential, high-oxygen flow favoured by hillstream loaches.
Because the Lake Tuz basin is an internally drained (closed) system with no outlet to the sea, its feeder streams and springs are a finite, easily disrupted resource: water abstraction, drought or pollution anywhere in the catchment can affect the whole population. This is a fish of small, spring-fed lowland-to-foothill watercourses, not large rivers, lakes proper, or brackish water.
Feeding
Oxynoemacheilus eregliensis is recorded with a trophic level of about 2.7, placing it as a lower-level, omnivorous consumer typical of small benthic stone loaches — foraging over the stream bed for small invertebrates, insect larvae and organic material, with some plant or detrital matter also taken. This matches the general pattern for Nemacheilidae as a family: bold micro-predators that pick prey off gravel and sand in clear, flowing water.
No aquarium-specific feeding data is available for this species in the sources consulted, so specific husbandry feeding advice here is inferred from its family rather than from a documented aquarium history. A keeper should assume it wants small live or frozen invertebrate foods (bloodworm, small crustaceans) and sinking foods rather than flake, in line with its wild micro-predator diet.
Mating
No courtship or spawning behaviour has been documented for Oxynoemacheilus eregliensis in the sources available; this is a narrow-range stream endemic with a small research literature, and its reproductive behaviour has not been directly studied or reported. Sexual dimorphism is likewise unrecorded for the species.
In the absence of species-specific data, the safest statement is the general pattern for stone and brook loaches (Nemacheilidae): egg-scattering over gravel in flowing water, without any pairing display, nest, or parental investment recorded in the family. Nothing more specific can honestly be said for this species.
Breeding
There is no record of Oxynoemacheilus eregliensis being bred in captivity. Following the pattern documented for Nemacheilidae generally, breeding is best understood as egg-scattering over gravel or among stones in fast-flowing water, with no parental care of eggs or fry.
This places it alongside the great majority of stone and brook loaches: rarely or never spawned by hobbyists, and absent from the aquarium trade entirely as far as available sources show. It is not farmed, hormone-induced, or otherwise produced commercially — it simply has no aquarium presence to document.
In the aquarium
Oxynoemacheilus eregliensis does not appear to be an aquarium fish in any meaningful sense; the sources consulted are entomological and ichthyological surveys of its native basin, not hobbyist or trade literature, and no maximum-size-appropriate tank recommendations, water-parameter husbandry notes, or trade history could be verified. Any care advice offered here would be extrapolation rather than documented fact, so none is given.
What can be said with confidence, extending from its family: like other nemacheilids it would be a scaleless, medication-sensitive fish that needs clean, well-oxygenated, flowing water and a soft or gravel substrate it can forage over — but a prospective keeper should treat this species as effectively unavailable and undocumented in captivity rather than plan around inferred care parameters.
Conservation
The IUCN Red List assessed Oxynoemacheilus eregliensis as Vulnerable (VU) on 9 January 2013, under criteria A2c+3c and B2ab(i,ii,iii,iv,v) — criteria that reflect both an observed or projected population decline linked to habitat degradation and a restricted, fragmented geographic range. This tracks directly with its biology: a species confined to a small number of streams and springs in a single closed drainage basin (with an additional population in the separate Lake Beyşehir basin) is inherently vulnerable to any disruption of that limited habitat, whether from water abstraction, drought, or pollution.
FishBase records no commercial fishing interest in the species and a low fishing vulnerability score, so exploitation is not the pressure here — habitat integrity in the Lake Tuz and Lake Beyşehir basins is. There is no evidence of any aquarium trade in this species, wild-collected or otherwise, in the sources reviewed.