Taxonomy & naming
Yunnanilus pleurotaenia was described by the English ichthyologist Charles Tate Regan in 1904, one of the earliest species assigned to what would later become the genus Yunnanilus — a name that itself means little more than "little fish of Yunnan," reflecting the genus's concentration in that province's lakes and streams. The species has at times been placed under older, broader generic names such as Nemacheilus or Noemacheilus, in keeping with the long history of the stone-loach group being lumped into a small number of catch-all genera before modern revisions split it apart; the Catalog of Fishes is the authority for the current valid combination, and this article follows the genus Yunnanilus as instructed by the source record.
The species sits in the family Nemacheilidae, the true stone or brook loaches — by far the largest family in the loach superfamily Cobitoidea, with well over 700 described species spread across South, Southeast and East Asia, the Himalayan and Tibetan plateau, and west into Central Asia and Europe. Within that family, Yunnanilus is one of several genera endemic to the lakes and karst streams of Yunnan, alongside relatives such as Triplophysa and Schistura found further west and north.
Morphology
Yunnanilus pleurotaenia is a small fish, reaching a maximum standard length of only about 2.5 in, in keeping with the generally diminutive size of the genus. Like other nemacheilids it has an elongate, cylindrical body, a small subterminal mouth suited to picking food from the substrate, and reduced or embedded scales that leave the skin close to naked — a trait shared across the loach superfamily that makes these fish notably sensitive to medication and copper-based treatments.
Counts recorded for the species include 10–12 dorsal rays, 8 anal rays, and 18–26 pored lateral-line scales, figures consistent with the fine-scaled taxonomy used to separate Yunnanilus species from one another. As in many stone loaches, an erectile suborbital spine is present beneath the eye — a defensive structure typical of the wider loach group, though modest in size compared to the prominent spines of the botiid loaches. Precise colour pattern and fin details for this species are not well documented in the sources available; readers should treat any photograph labelled with this name with some caution, since Yunnanilus is a taxonomically dense genus with many superficially similar species.
Habitat
This species is endemic to the Dian Lake basin in Yunnan Province, southwestern China, where it is known from the lake's associated streams rather than open lake water itself. Dian Lake sits on the Yunnan-Guizhou Plateau at high elevation, and its tributary streams run cool, clear and well-oxygenated over rocky or gravel substrates — classic stone-loach habitat, where the fish forages along the streambed rather than in open water.
FishBase classifies the species as a subtropical, demersal freshwater fish, consistent with its plateau setting: not a warm lowland tropical species, and not a cold high-alpine one either, but a moderate, flowing-water fish of the Yunnan uplands. The Dian Lake basin has undergone heavy urban and agricultural development around the city of Kunming over recent decades, and this has degraded water quality and habitat across the basin's stream network — a pressure discussed further under Conservation.
Feeding
Yunnanilus pleurotaenia is a benthic micro-predator. Stomach content data cited by FishBase records small crustaceans and gammarid amphipods as prey items, the classic diet of a stone loach working the gravel and cobble of a fast-flowing stream for invertebrates. This fits the broader pattern seen across Nemacheilidae, where species pick insect larvae, small crustaceans and other invertebrates from the substrate rather than grazing algae or biofilm in the manner of hillstream loaches.
In an aquarium setting this diet translates to small sinking foods: finely crushed pellets, frozen bloodworm, daphnia, brine shrimp and other small live or frozen invertebrate foods offered at the bottom, since a fish this size and this specialised is unlikely to compete well for food at the surface or in midwater.
Mating
No specific courtship or spawning behaviour has been documented for Yunnanilus pleurotaenia in the sources available. Data on reproduction in this species is sparse, which is typical for many narrow-range stone-loach endemics that have received far more attention from conservation assessors than from aquarists or breeders. What can be said comes from the wider genus and family: related small Yunnanilus and other nemacheilid species are egg-scattering fish with no pair-bonding or nest-building behaviour reported, spawning opportunistically rather than through elaborate courtship.
Breeding
As with most stone and brook loaches, Yunnanilus pleurotaenia is not known to be bred in the home aquarium, and detailed breeding accounts for the species do not appear in the available sources. The pattern documented for the wider genus — illustrated by the more commonly kept Yunnanilus cruciatus — is egg-scattering over the substrate in well-oxygenated water with some flow, with no parental care of eggs or fry afterward. There is no evidence of any cave-guarding, mouthbrooding or other elaborate reproductive strategy in this group; loaches in general, and Nemacheilidae in particular, are egg-scatterers.
Given the species' restricted native range and its Vulnerable status, most individuals reaching the hobby, if any, would be expected to come from wild collection rather than captive propagation — though the available sources give no indication this species is meaningfully present in the aquarium trade at all.
In the aquarium
Yunnanilus pleurotaenia is essentially unknown in the aquarium trade, and the available sources offer no dedicated care profile for the species. What can be inferred is limited to its biology and to the general care pattern for small nemacheilid stone loaches: cool-to-moderate, clear, well-oxygenated flowing water over a fine gravel or sand substrate, since this is a stream fish adapted to current rather than still water. Its near-scaleless skin, typical of the loach superfamily, means any specimen in captivity should be treated cautiously with medications and never dosed with copper-based treatments at full strength.
Given its small adult size of around 2.5 in and benthic, invertebrate-picking habits, a specimen tank would need to prioritise oxygenation, flow and a soft, fine substrate over decoration. Because so little is documented about this species specifically, and because it is a threatened, narrow-range endemic, keepers should not treat any anecdotal availability as a reason to acquire wild-collected stock; this is a species better appreciated through its conservation story than sought for a tank.
Conservation
Yunnanilus pleurotaenia is assessed by the IUCN as Vulnerable (VU), reflecting its restriction to a single lake basin — Dian Lake and its associated streams in Yunnan — a classic risk profile for narrow-range lake endemics. The assessment dates to 2011. Dian Lake sits adjacent to the rapidly urbanising city of Kunming, and the basin has experienced significant pollution, eutrophication and habitat modification pressure over recent decades from agricultural runoff and urban development, the kind of pressure that disproportionately affects small-range stream and lake endemics that cannot simply relocate to unaffected water.
There is no indication in the available sources that the aquarium trade plays any meaningful role in this species' conservation status; the pressures are habitat- and pollution-driven rather than collection-driven. As with many Yunnan lake-basin endemics, its long-term prospects are tied to the health of the Dian Lake watershed as a whole.