Taxonomy & naming
Oxynoemacheilus bergi was described by Vladimir Gratzianov in 1907, in the Trudy Otdela Ichtiologii (the proceedings of the ichthyology section of the Imperial Society for Acclimatisation), as Nemacheilus bergi. The species commemorates Lev Semyonovich Berg (1876-1950), the Russian ichthyologist and geographer who had collected the original specimens, though it was Gratzianov who formally described and named the fish.
For most of the twentieth century the species travelled under Nemacheilus or Noemacheilus, the old catch-all genera into which most Eurasian stone loaches were once lumped. The family Nemacheilidae has since been extensively revised, and the Caucasian and Anatolian stone loaches with a slender body and a particular arrangement of head pores and lateral-line scales were split out into Oxynoemacheilus. The Catalog of Fishes, the governing authority for valid names, currently places this species there, as Oxynoemacheilus bergi, in family Nemacheilidae — the parenthesised authority signalling the original genus reassignment. The name Oxynoemacheilus lenkoranensis is treated as a synonym of this species in Eschmeyer's Catalog of Fishes.
Morphology
This is a small, slender stone loach, elongate and only weakly compressed, in keeping with the general Nemacheilidae body plan. A specimen from the Kura River has been recorded at 2 in standard length, and type material collected by Berg measured 2.5 in and 1.5 in — together suggesting a typical adult range of roughly 1.5–2.5 in, small even by loach standards.
As in other Oxynoemacheilus and related nemacheilids, the skin carries minute embedded scales rather than a true scaled covering, leaving it functionally near-naked and, by extension, sensitive to poor water quality and heavy-handed medication. Many stone loaches in this family also bear a small erectile spine below the eye; detailed published descriptions of this species' head and fin morphology are limited, so its exact expression here is not confirmed and should not be overstated. Overall build and habits mark it as a bottom-hugging micro-predator built for holding position in current.
Habitat
Oxynoemacheilus bergi is known from the Kura-Aras river system of the South Caucasus, with its type locality in the Akstafa (Agstafa) River — a right-bank tributary of the Kura in Azerbaijan — and further records from the Aras drainage and from Turkey. This places it among the many small, often single-drainage-endemic stone loaches of the Caucasus and Anatolia.
It lives in freshwater stream habitat typical of the genus: fast-flowing, clear, well-oxygenated water over stone and gravel substrate. A closely related Kura-basin species, O. brandtii, is documented in subtropical streams around 50–68 °F, and this species is presumed to occupy similar cool-to-moderate, flowing water rather than warm, still conditions. No dedicated habitat survey specific to O. bergi has been located, so finer detail on seasonal temperature range, gradient or substrate preference remains unconfirmed.
Feeding
Oxynoemacheilus bergi is a benthic micro-predator, the standard mode for stone and brook loaches: it forages over stream-bed stone and gravel for small invertebrates, picking at insect larvae and other benthic crustaceans dislodged by the current. No dedicated dietary study of this species has been published, so this picture is inferred from its morphology and from the well-documented feeding ecology of its genus and family rather than from direct observation.
No aquarium feeding records exist for this species. Were it kept, the expectation from its wild niche would be a reliance on small live or frozen invertebrate foods and sinking preparations rather than flake, though this has not been tested in captivity.
Mating
Nothing specific has been published on courtship or spawning behaviour in Oxynoemacheilus bergi. No external sexual dimorphism has been documented for this species, and the sexes are presumed to look broadly alike, as in many small nemacheilids, though this has not been formally studied.
Breeding
As with the great majority of stone and brook loaches (Nemacheilidae), Oxynoemacheilus bergi is presumed to be an egg-scatterer, releasing eggs over gravel or among stones in flowing water with no parental care — the standard reproductive mode across the family. There is no record of this species being bred, or even held, in the aquarium, and no field study of its spawning has been located. This is a case where the honest answer is that data is sparse: breeding biology should be treated as unknown rather than assumed.
In the aquarium
Oxynoemacheilus bergi has no documented aquarium history — it does not appear to be established in the hobby, and no husbandry notes, import records or care reports have been found. Anyone encountering a fish under this name should treat the identification with caution, given how easily small Caucasian and Anatolian stone loaches are confused with one another and with related Oxynoemacheilus and Barbatula species.
Were it ever kept, its wild niche points to the general stone-loach template shared across this family: cool-to-moderate, clean, fast-flowing, well-oxygenated water over stone and gravel, and — as for all near-scaleless loaches — caution with copper-based and full-strength medications. None of this is confirmed by direct husbandry experience for this species, and at present it should be regarded as essentially unavailable and unkept in the trade.
Conservation
Oxynoemacheilus bergi has not been assessed on the IUCN Red List; no species-specific assessment page could be located, so it is recorded here as Not Evaluated rather than assigned a guessed category. As a small, apparently single-river-system endemic of the Kura-Aras drainage spanning Azerbaijan and Turkey, it shares the general vulnerability profile of many narrow-range Caucasian stream loaches, whose habitats face pressure from water abstraction, damming and pollution across the region — but no population trend or threat data specific to this species has been published. There is no evidence of any aquarium-trade pressure on this species, wild-collected or otherwise.