Taxonomy & naming
Physoschistura pseudobrunneana was described by the Swiss ichthyologist Maurice Kottelat in 1990, with its type locality given as the Nam Mae Lao at kilometres 62 and 65 on the Chiang Mai–Chiang Rai road, Chiang Rai Province, Thailand — part of the middle Mekong River drainage. The species epithet, built on "pseudo-" plus "brunneana," signals that it was described as a close relative of, and easily confused with, Physoschistura brunneana, the type species of the genus.
It belongs to Nemacheilidae, the stone and brook loaches, by far the largest loach family with roughly 790 described species spread across Eurasian streams. The genus Physoschistura is defined in part by details of the air bladder — a capsule with two halves joined medially and a free posterior chamber — and its members are distributed through the upper Brahmaputra, Irrawaddy, Salween and Mekong drainages. The Catalog of Fishes is treated as the authority for the valid combination, and it is retained here as Physoschistura pseudobrunneana; there is no indication in the available sources of a more recent generic reassignment.
Morphology
Like other members of its genus, Physoschistura pseudobrunneana is a small, elongate, nearly cylindrical loach, built low and slender for holding position on the stream bed. Sources describing the genus put its relatives in the range of a few centimetres in total length — for comparison, the congener P. rivulicola is recorded to about 2 in — and there is no indication this species departs from that small-bodied pattern.
As a nemacheilid, it is a near-scaleless fish, its skin only lightly and inconspicuously scaled, a trait that matters for how it should be handled and medicated in captivity. Detailed published data on its colour pattern, fin counts and other diagnostic morphology beyond the original 1990 description do not appear in the sources available here, so this remains, honestly, a thinly documented species outside the taxonomic literature.
Habitat
The species is known from the middle Mekong River basin of northern Thailand, specifically the Nam Mae Lao drainage in Chiang Rai Province — a clear, fast-flowing stream system typical of the hill country between Chiang Mai and Chiang Rai. Physoschistura as a genus occupies clear, fast, oxygen-rich mountain and foothill streams across its wider Southeast and South Asian range, and there is nothing in the record to suggest this species differs from that pattern.
This is a running-water fish of cool-to-moderate hill streams, not a still-water or blackwater species: it should be understood as living over clean gravel and stone substrate in current, with good oxygenation, rather than in the slow, soft, warm conditions often assumed for "loaches" generically.
Feeding
Nemacheilid stone and brook loaches, including the Physoschistura group, are bottom-dwelling micro-predators, working the substrate of fast streams for insect larvae and other small invertebrates. Species-specific dietary data for P. pseudobrunneana has not been published, but its feeding ecology is best inferred from this well-established family pattern rather than assumed to be generalist or vegetarian.
In practical terms this points to a fish that would take small live and frozen invertebrate foods readily and may be slow to recognise flake or pellet, though no aquarium feeding records for the species itself exist in the sources reviewed here.
Mating
No species-specific information on courtship, sexing or spawning behaviour for Physoschistura pseudobrunneana appears in the available sources. Nemacheilid loaches as a family are described as rainy-season spawners, releasing eggs over gravel and stones in fast current as water levels rise, with no evidence of pairing behaviour beyond that seasonal cue. Absent direct observation of this species, that family-level pattern is the most that can honestly be said.
Breeding
Physoschistura pseudobrunneana has no documented aquarium or field breeding record in the sources available. Stone and brook loaches (Nemacheilidae) as a group are egg-scatterers: ripe fish release eggs over gravel and among stones in fast-flowing water with no parental care whatsoever, typically timed to monsoon rains. They are rarely bred in captivity, and this obscure, little-collected species is no exception — there is no record of it having been spawned in an aquarium.
In the aquarium
Physoschistura pseudobrunneana is not established in the aquarium hobby, and no husbandry record for the species exists in the sources consulted here. Based on its genus and family, a keeper attempting it should provide cool-to-moderate, clear, well-oxygenated, flowing water over a gravel or stone substrate rather than a warm, still community tank — the opposite of what many casual buyers picture when they hear "loach."
As with other nemacheilids, its near-scaleless skin makes it sensitive to copper and full-strength medications, so any treatment should be approached cautiously and at reduced dose. Given the total absence of trade or care data, this is a species to treat as a research curiosity rather than a stocking recommendation.
Conservation
Physoschistura pseudobrunneana is listed by IUCN sources referenced here as Least Concern, though the specific assessment year and supporting document were not captured in the available cache. It is known from the Nam Mae Lao and the wider middle Mekong drainage of northern Thailand; like many small-range Southeast Asian stream loaches, it depends on the ongoing clarity, flow and oxygenation of its home streams, and habitat degradation in hill-country catchments is the general pressure category for fish of this kind, though no species-specific threat assessment is documented here. It is not known to be part of the aquarium trade, so trade pressure is not a relevant factor for this species.