Taxonomy & naming
Schistura udomritthiruji was described in 2010 by Peter Bohlen and Vendula Šlechtová as a new loach from southern Thailand, placed from the outset in the genus Schistura within the family Nemacheilidae, order Cypriniformes. The species epithet honours Kamphol Udomritthiruj, a Thai aquarist — the same honorific independently attached to an unrelated species, Botia udomritthiruji Ng, 2007, a Myanmar botiid from the Tanintharyi drainage. The two are easy to confuse by name alone but are entirely distinct fish in different families: the Botia species is a larger (4.5–6 in), dark-blotched Botiidae from Myanmar rivers, of Data Deficient status, while Schistura udomritthiruji is the diminutive Nemacheilidae stone loach treated here.
Within Schistura, the species sits in the S. multifasciata species group and is distinguished from closely related congeners such as S. vinciguerrae chiefly by the structure of the suborbital flap present in males. As with much of this genus, older literature and aquarium sources may still refer to related fish under the defunct Nemacheilus or Noemacheilus, but the Catalog of Fishes governs Schistura as the valid current combination for this species.
Morphology
This is a small, slender stone loach, reported at a maximum of about 2 in standard length, with specimens from the type series recorded as small as 1 in SL. Like other Nemacheilidae it has the classic "true loach" build: an elongate, sub-cylindrical body, a small ventral mouth suited to picking food off the substrate, and barbels around the mouth for tactile foraging. The skin is effectively naked, carrying the tiny, deeply embedded scales typical of the family rather than the more obvious scaling of many other freshwater fish — a trait that makes members of this group sensitive to medication.
The species carries the erectile suborbital spine characteristic of many loaches, used defensively and diagnostically by taxonomists, and males possess a suborbital flap whose shape is one of the key characters separating S. udomritthiruji from its closest relatives in the S. multifasciata group. Beyond the type description, detailed colour-pattern and fin-count data are not captured in the sources available here; this remains a data-sparse species outside the primary taxonomic literature.
Habitat
Schistura udomritthiruji is known from streams draining to the Andaman Sea in southern Thailand, between Takua Pa and Ranong. The type locality is described as a stream roughly 26 ft wide with a maximum depth of about 15.5 in, running over gravel riffles and scattered rocks — classic fast, shallow, well-oxygenated stone-loach habitat. Water at the type locality was recorded as warm (around 84 °F) and distinctly alkaline (pH 8.0 or higher), which is on the warmer and harder side of what is typical for the genus as a whole.
As with most Schistura, this is a benthic fish of clear, flowing water rather than still or blackwater habitat, and it is tied closely to the specific gravel-and-rock stream structure of its native drainages. Given how narrow its known range is — a short stretch of coastal southern Thailand — it should be treated as a stream-restricted species until further survey work says otherwise.
Feeding
FishBase places Schistura udomritthiruji at a benthic trophic level of about 3.0, consistent with the genus's general habit as a bottom-foraging micro-predator: picking small invertebrates, insect larvae and other tiny stream-bed organisms from among gravel and rock. This tracks the wider pattern for Nemacheilidae, which are active hunters of the stream floor rather than grazers or scavengers of decaying plant matter.
No aquarium feeding data exists for this species specifically, but going by its close relatives, it would be expected to take small live and frozen foods (bloodworm, daphnia, brine shrimp) and sinking pellets readily, while showing little interest in flake left to float at the surface.
Mating
No courtship or spawning behaviour has been documented for Schistura udomritthiruji in the sources available. The species was described from preserved type material collected in the wild, and detailed reproductive biology — sexual dimorphism beyond the male suborbital flap, seasonal spawning triggers, or courtship behaviour — has not been studied or published for this fish specifically.
Breeding
This species is not known to have been bred in the aquarium. Stone and brook loaches of the genus Schistura are, as a rule, egg-scatterers that release eggs over gravel in fast-flowing water with no parental care, and Schistura udomritthiruji almost certainly follows that pattern, but no direct observation of spawning — wild or captive — has been recorded for it. It should be treated as an unbred, data-sparse species rather than assigned a confident breeding protocol.
In the aquarium
Schistura udomritthiruji is not an established aquarium fish; it is essentially unknown in the hobby and no husbandry track record exists for it. Extrapolating cautiously from its close relatives and its natural habitat, a keeper attempting this species would want a tank replicating fast-flowing, well-oxygenated, gravel-bottomed stream conditions with warm water and hard, alkaline chemistry — a setup closer to a small hillstream biotope than a typical still community tank.
As with other Nemacheilidae, the near-scaleless skin means any wild-collected specimens should be handled cautiously with medications, using gentle, reduced-dose treatments rather than full-strength doses formulated for scaled fish. Given the total absence of trade or husbandry history, anyone encountering this species would effectively be working from first principles.
Conservation
The IUCN Red List assessed Schistura udomritthiruji as Least Concern in 2011, shortly after its description. That said, the species is known only from a narrow band of streams in southern Thailand's Andaman-draining coast, so its status merits periodic review as habitat pressure in the region — deforestation, water extraction and development along coastal Thai watersheds — continues. There is no evidence of aquarium-trade collection pressure on this species; it does not appear to be part of the ornamental trade.