Taxonomy & naming
The species was first noticed in 1979 by the speleologist V. N. Maltsev, who reported blind fish in a flooded gypsum cave in the Kugitangtau range, and specimens were collected in 1981 by Swerden. The Russian ichthyologist Nikolai Parin formally described the fish in 1983, erecting a new genus, Troglocobitis, to hold it. It has occasionally been placed in the older, broader genera Nemacheilus, Noemacheilus or Paracobitis in general reviews of Central Asian loaches, but the Catalog of Fishes — the standing authority for valid names — confirms Paracobitis starostini as the accepted combination, with Parin as sole author and 1983 as the date of description.
Troglocobitis is monotypic: P. starostini is the only species in the genus, and the genus itself is endemic to this one cave system, making it a taxonomic as well as a geographic singleton. It belongs to Nemacheilidae, the stone and brook loaches, the largest family of true loaches and the one that supplies most of the world's small, clear-stream micro-predator loaches — though this particular member never sees a stream at all.
This fish was long listed as Troglocobitis starostini; Eschmeyer's Catalog of Fishes places the species in Paracobitis, and the current combination Paracobitis starostini is followed here.
Morphology
Paracobitis starostini is small even by nemacheilid standards: the holotype measures 1.95 in standard length, with paratypes ranging 1.44–2.4 in SL. Like other obligate cave fish it shows the classic suite of troglobitic, or 'regressive,' adaptations that evolve convergently wherever a fish population becomes permanently isolated underground: it has no functional external eyes, no body pigmentation, no true scales, and no swim bladder. These are not defects but the predictable signature of a lineage that has spent a very long time in a lightless, food-poor, thermally stable environment where vision and colour serve no purpose and energy is better spent elsewhere.
As a nemacheilid it retains the family's general body plan — an elongate, rounded-in-cross-section loach body suited to hugging the bottom — but the reduction of scales and the total loss of eye function set it apart sharply from its sighted, patterned relatives in the surface streams of Central and South Asia. Data on fin ray counts, barbel number and other fine anatomical detail beyond the original description are sparse; this account does not extend beyond what has been documented.
Habitat
The entire known world of this species is a single underground lake in Provull Gypsum Cave — also recorded as the Suvly-Oyuk sinkhole — in the Kugitangtau (Koytendag) Mountains of Lebap Province, in far eastern Turkmenistan near the border with Uzbekistan. The lake itself is tiny, on the order of 40 square metres of surface area, with a depth of roughly 5–7 metres, sealed inside a karst gypsum cave system with no natural light. No other population or locality has ever been recorded, anywhere.
Specific water chemistry and temperature have not been published, but the physical setting is informative: groundwater held inside a mountain karst system at roughly 40°N latitude is buffered from surface seasons and is very likely cool and thermally stable year-round, not warm and fluctuating like a lowland tropical stream. The water is clear, still to very slow-moving, and permanently dark — a fundamentally different environment from the fast, oxygen-rich riffles that most of this species' free-living nemacheilid relatives inhabit.
Feeding
No dietary study has been published for Paracobitis starostini specifically. By family and inferred from other Nemacheilus-group loaches, it is presumed to be a benthic micro-predator, picking small invertebrates off the cave floor and sediment. Cave lakes are food-poor environments — there is no photosynthesis to drive a food web, only whatever organic matter washes or drips in from above — so any resident fish population necessarily survives on a sparse, irregular supply of small invertebrates and detrital material, and is likely to grow slowly as a result.
Because the species has never been kept or studied in captivity, there is no aquarium feeding record to draw on. This account keeps to what the family and setting reasonably support rather than inventing specifics.
Mating
No courtship or spawning behaviour has been documented for this species. Nothing is published on sexual dimorphism, size at maturity, or seasonal cues, and given the total isolation and stability of a cave-lake environment, any breeding cycle is unlikely to follow the flood-season triggers seen in surface-dwelling relatives. This is a genuine data gap, not an omission — the species is known essentially from its original description and subsequent brief surveys, not from ongoing life-history research.
Breeding
There is no aquarium breeding record for Paracobitis starostini — it has never been part of the fishkeeping hobby. Based on the general pattern for nemacheilid stone and brook loaches, which are egg-scatterers with no parental care, any natural reproduction in the cave lake is presumed to follow the same basic mode: eggs released over the substrate with no guarding behaviour. This is an inference from the family, not an observed fact for this species, and should be read as such.
Given the extreme rarity, total habitat restriction and lack of trade interest, this is a species that is best understood, not collected — it will not be bred at home, and there is no realistic or responsible route to trying.
In the aquarium
Paracobitis starostini is not, and should not be, an aquarium fish. It has no history in the trade, no known captive husbandry, and a wild population confined to a single 131 ft² cave lake — a population so small and so narrowly restricted that any collection pressure at all could be catastrophic. There is nothing responsible to recommend here beyond leaving this species alone in the wild.
Its value to this atlas is as a natural-history subject: a demonstration of just how far a fish lineage can diverge when isolated underground, and a reminder that the loach order's diversity runs from bold, sociable community fish like the clown loach all the way to a blind, colourless, one-lake endemic that most ichthyologists will never see alive.
Conservation
The IUCN Red List assesses Paracobitis starostini as Vulnerable. That status reflects the defining fact about this species: its entire global population is confined to one small underground lake in one cave system, with no other locality known. A population this restricted is inherently fragile — any disturbance to the cave's hydrology, water quality or physical access, whether from mining, groundwater extraction, tourism or local disturbance in the Kugitangtau karst, could threaten the only place this fish exists.
There is no aquarium trade in this species and no evidence it has ever been collected for that purpose; its risks are purely habitat-driven. As the only cavefish known from all of Central Asia, it is also a conservation and scientific singleton, disproportionately valuable relative to its tiny numbers, and a case where 'do not disturb' is the entire management prescription.