Taxonomy & naming
Protocobitis polylepis was described by Zhu, Lü, Yang & Zhang in 2008, one of a small handful of species placed in the genus Protocobitis, itself established by Yang & Chen in 1993. The genus sits in the family Cobitidae, the true spined and pond loaches — the group that gives the whole loach lineage its name, on the strength of the erectile suborbital spine shared across its members.
Cobitidae is an Old World family of roughly 260 species, overwhelmingly Eurasian, and Protocobitis belongs to a small cluster of subterranean, blind Cobitidae described from cave and aquifer systems in southern China — a striking example of how a family best known for sunlit gravel-bed streams also contains a handful of obligate cave specialists. The species epithet polylepis is standard Greek loach-naming vocabulary ("many-scaled"), distinguishing it from congeners on scale-count grounds; as with most of this genus, taxonomic treatment rests almost entirely on the original description, and no synonymy or revision is documented in the sources available here.
Morphology
Protocobitis polylepis is diminutive even by loach standards, reaching only about 1 in standard length in males and unsexed individuals and around 1.5 in SL in females — a fish that would fit comfortably on a fingertip. As a member of Cobitidae it carries the family's signature erectile suborbital spine, a small blade-like structure folded into a groove beneath the eye that can be flicked out, and it shares the family's near-scaleless, delicate skin despite the "many-scaled" epithet, which refers to scale count rather than scale coverage.
Living its entire life without light, it shows the classic troglobitic (cave-adapted) suite: eyes are reduced or absent and body pigment is lost or greatly diminished, trading vision and colour for the sensory barbels and lateral-line sensitivity that let it navigate and forage by touch in total darkness. This is a coolwater, subterranean fish — not a tropical, surface-stream species like most of its Cobitidae relatives — and its body plan reflects a life spent entirely underground in the karst aquifers of Guangxi.
Habitat
The species is known only from a single underground water source near Wuming County, Guangxi Province, in southern China — the type locality and, as far as documented, the only place it has ever been recorded. This is karst terrain, a landscape of limestone riddled with caves, sinkholes and subterranean rivers, and Protocobitis polylepis lives within that hidden aquifer system rather than in any surface stream.
Conditions in a stable underground aquifer are cool and thermally constant year-round, buffered from the seasonal swings of surface water, and the surrounding limestone geology typically produces neutral to mildly alkaline water. No detailed physicochemical survey of the site is available in the sources here, so exact temperature and pH figures for this specific cave system are not documented — but the habitat itself, an isolated subterranean water body in karst limestone, is well established and is the single most important fact about the species.
Feeding
Documented diet data for Protocobitis polylepis is not available, but its family placement and cave-adapted body plan point clearly to a benthic scavenger, in keeping with Cobitidae as a whole: these are sand- and sediment-sifting omnivores that forage over the substrate for small invertebrates and organic detritus rather than hunting by sight. In a lightless aquifer, feeding by touch and chemoreception — using barbels and a sensitive lateral line to locate food in the sediment — would be the only option available to it.
No specific prey items, feeding behaviour, or captive diet have been documented for this species in the available literature; any statement more specific than "benthic detritivore/scavenger typical of the family" would be speculation beyond what the sources support.
Mating
No courtship, spawning trigger, or reproductive behaviour has been documented for Protocobitis polylepis. Nothing is known about how or when this species pairs or spawns in its cave habitat, and given how rarely it has even been observed, that gap is unsurprising — this is one of the most poorly studied loaches covered here.
Breeding
There is no confirmed breeding record for Protocobitis polylepis in the wild or in captivity, and the species is not known to be kept or bred in aquaria at all. By family pattern, Cobitidae are egg-scatterers with no parental care, and several temperate spined and pond loaches — species of Cobitis, Sabanejewia, and the dojo or weather loach Misgurnus — are known to scatter adhesive eggs among vegetation, typically in spring, with some of those temperate species having been pond- or tank-spawned by hobbyists and researchers. Protocobitis polylepis, however, is not one of those documented cases: as a permanently subterranean species with no seasonal light cues and a single known population, it almost certainly does not follow a conventional spring-spawning pattern, and no such trigger has ever been recorded for it.
The honest summary is that breeding in this species has never been documented, in the wild or in the aquarium. If it follows the family's general egg-scattering mode, parental care would be expected to be absent — but even that is inference from its relatives rather than direct observation of this fish.
In the aquarium
Protocobitis polylepis is not an aquarium fish. It does not appear in the ornamental trade, has no documented aquarium husbandry, and — as a Critically Endangered, single-locality subterranean endemic — should not be collected or kept even if specimens were ever offered. There is no care profile to give here beyond the general cautions that apply to Cobitidae as a family: near-scaleless skin makes these fish sensitive to copper and full-strength medications, and a soft sediment substrate is essential to any sand-sifting loach's natural feeding behaviour.
For a species this data-sparse and this narrowly restricted, the correct posture for any keeper or institution is conservation-minded observation, not acquisition — its entire global population inhabits one underground water source, and any collecting pressure at all could be consequential.
Conservation
The IUCN Red List assesses Protocobitis polylepis as Critically Endangered (CR), classified under criteria B1ab(iii)+2ab(iii), as of a 2017 assessment (per FishBase). That classification reflects the species' extraordinarily restricted range — known from just one underground water source near Wuming County, Guangxi — combined with an inferred ongoing decline in the extent or quality of its subterranean habitat.
Single-site cave and aquifer endemics like this one are acutely vulnerable to karst groundwater disruption: quarrying, water extraction, pollution infiltration and hydrological changes to the aquifer system can affect the entire known population at once, since there is no second site to buffer against loss. Protocobitis polylepis is not part of the aquarium trade and faces no documented collection pressure; its conservation risk is a habitat story, tied to the fate of one specific karst water source in Guangxi Province.