Taxonomy & naming
Sinogastromyzon wui was described by the Chinese ichthyologist Ping-Cheng Fang in 1930, placing it in the genus Sinogastromyzon — a name that had been erected by Fowler in 1905 for this cluster of small, flattened hillstream fishes endemic to East and Southeast Asia. The genus belongs to the family Balitoridae (hillstream loaches), the most morphologically specialised of the loach lineages, whose members have evolved independently flattened bodies, broad paired-fin discs, and specialised mouths for life on rock in fast water.
Sinogastromyzon currently contains around 16–20 species, most poorly documented and with narrow endemic ranges in the hill-stream systems of southern China, Indochina, and adjacent Sundaland. S. wui is one of the more obscure members; its original description predates the Catalog of Fishes digital era, and no synonymies or subsequent name changes are recorded. The Catalog of Fishes (Eschmeyer, CAS) lists Sinogastromyzon wui Fang, 1930 as the valid combination, and that remains the name in current use. Closely related species — S. tonkinensis (from Tonkin/northern Vietnam) and S. chapaensis — share the same care requirements and similar Data Deficient conservation status.
Morphology
Like all members of Sinogastromyzon, S. wui is radically flattened dorsoventrally — the body forms a low, streamlined disc in side profile, with the head broad and depressed and the abdomen flat against the rock. The pectoral and pelvic fins are greatly expanded and held horizontally, functioning together as an adhesive surface that keeps the fish pressed against substrate in fast current. This is convergent evolution, not a true sucker disc in the way of remoras; the fish grips by hydrodynamic pressure and friction, not by muscular suction.
Adults reach approximately 3 in in standard length, making this a small species even by hillstream standards. The body is essentially scaleless to the touch — the tiny, deeply embedded scales offer little barrier — which matters significantly for medication. Coloration is cryptic: a mottled brown to olive-tan pattern over a pale underside, the pattern varied in intensity to blend with the rock and sand of the stream bed. A suborbital spine is present, as in most balitorids, though it is less prominent than in the botiid loaches.
Habitat
Sinogastromyzon wui is native to the hill streams of southern China, with related congeners distributed across Indochina (northern Vietnam, Laos) and adjacent drainages. The habitat is fast-flowing, shallow, rocky stream sections — riffles and rapids where the current is strong enough to maintain high dissolved oxygen and keep the substrate scoured clean of sediment. The water is cool (68–75 °F), highly oxygenated, clear to lightly turbid, and typically soft and close to neutral in pH.
The substrate is smooth pebbles, cobbles, and exposed bedrock, all coated in the biofilm of algae, diatoms, and microorganisms that constitutes the fish's primary food source. Vegetation is sparse or absent in the fastest sections; the fish relies on the physical texture of rock rather than plant cover for shelter. Seasonal variation in flow and temperature marks the annual cycle; the streams warm and recede in dry seasons and run fast and cool again with the monsoon rains.
Feeding
Sinogastromyzon wui is primarily a biofilm grazer — it uses its modified, downward-facing mouth to rasp aufwuchs (the community of algae, diatoms, bacteria, and organic detritus adhering to rock surfaces) directly off stone. This is its principal and preferred food source in the wild, and the reason that a mature rockscape cloaked in established biofilm is not optional in the aquarium but essential. A fish introduced into a bare, newly set-up tank will find nothing to eat on the rocks and will decline rapidly.
Beyond biofilm, S. wui is known to take small invertebrates — microcrustaceans, insect larvae, and other zoobenthos — as a protein supplement. In the aquarium this translates to small frozen foods such as Daphnia, baby brine shrimp, and micro-worm, along with blanched greens (courgette, cucumber, spinach) and quality sinking wafers that contain a high proportion of vegetable matter. Variety is important; a diet of biofilm alone in captivity may be insufficient for long-term health. Feeding after lights-out, when the fish are most active on the substrate, is good practice.
Mating
Sexual dimorphism in Sinogastromyzon wui is not well documented; what is known from the genus suggests that ripe females are somewhat plumper-bodied than males when in breeding condition, but the two sexes are otherwise difficult to distinguish externally. This makes selecting a pair deliberately — rather than relying on a group — more a matter of chance than of deliberate pairing.
In the wild, spawning is presumed to be linked to seasonal changes in water temperature and flow that accompany the monsoon, as is the case for most rheophilic hillstream fishes. The combination of cool, fast, highly oxygenated water and a biofilm-rich substrate appears to constitute the environmental cues that bring fish into condition. Replicating those cues — particularly the sustained cool temperatures and powerful current of a mature, established river tank — is the prerequisite for any realistic attempt at spawning in captivity.
Breeding
Sinogastromyzon wui is an egg-scatterer with no parental care, depositing adhesive eggs among the interstices of the gravel and stone substrate in fast water. The eggs develop in the current, and neither parent guards or tends them. This is the general pattern for hillstream balitorids.
The species is almost never bred in home aquaria; it is rarely available in the trade at all, and verified captive spawnings are not documented in the mainstream hobby literature. A small number of dedicated hillstream keepers report that some Sinogastromyzon species will spawn spontaneously in a mature, strongly flowing river-tank setup with appropriate cool temperatures, but confirmed accounts for S. wui specifically are absent. The correct expectation is that this fish will not breed in a typical home aquarium: the keeper should focus on its long-term health and biofilm diet rather than on reproduction. The trade supply is from wild collection, not captive breeding.
In the aquarium
Sinogastromyzon wui is a specialist for the experienced hillstream keeper, and almost every way it is killed in captivity comes down to one of three failures. The first is temperature: this is a cool-water fish that needs 68–75 °F. At tropical community temperatures (79–82 °F) it declines over weeks. An unheated room-temperature tank — or in warmer climates, a dedicated chiller — is required.
The second failure is flow and oxygenation. The fish evolved in torrents; it needs powerful, turbulent flow that keeps dissolved oxygen at or near saturation. A gentle hang-on-back filter in a still tank is not adequate. A high-flow powerhead directed along a bank of smooth pebbles, with strong surface agitation, is the minimum. The third failure is diet: the tank must be mature enough to have a visible coat of algae and biofilm on every rock surface before this fish is introduced. A bare or newly established aquarium offers it nothing to eat and it will starve silently over several weeks.
Given these requirements, a 75 × 12 in footprint or larger is appropriate. Décor should be smooth cobbles and pebbles — nothing abrasive to the fish's soft, near-scaleless underside. Tankmates should be limited to other hillstream species or very fast-water small fish; it should not be kept with large, boisterous, or warm-water species. Because it is near-scaleless, it is sensitive to copper-based treatments and to full-strength medication doses; use only half-doses of any treatment, and remove it to an unmedicated hospital tank if possible when treating for disease.
Conservation
Sinogastromyzon wui is assessed as Least Concern (LC) by the IUCN Red List. Like most members of its genus, it lives in the hill streams of southern China, a habitat type subject to pressure from deforestation (which increases siltation and water temperature), dam construction, and agricultural runoff — pressures that affect the group generally but that the current assessment does not consider sufficient to place this species in a threatened category.
The aquarium trade in S. wui is negligible; it appears only sporadically in the specialty market, and all traded individuals are wild-collected since captive breeding is not established. Keepers who obtain this fish should still prioritise the conditions it needs to thrive, since the long-term health of its native streams remains the real determinant of the species' status.