Taxonomy & naming
Haotula sonlaensis was described in 2010 by Nguyen, Nguyen & Hoang, with the species epithet taken directly from Son La, the city and province in northwestern Vietnam where the type material was collected. It sits in the genus Schistura, part of the family Nemacheilidae — the stone or brook loaches, by far the largest family within the loach superfamily Cobitoidea and one that has absorbed many species formerly split across older genera such as Nemacheilus and Noemacheilus.
Nemacheilidae taxonomy is actively revised, and this species is no exception: recent work (Endruweit, 2025) has proposed moving some Schistura, including this species, into a newly erected genus, Haotula. That reclassification is not yet the settled combination across the literature, so this profile keeps the currently used name, Haotula sonlaensis, and flags the possible future change rather than pre-empting it.
This fish was long listed as Schistura sonlaensis; Eschmeyer's Catalog of Fishes places the species in Haotula, and the current combination Haotula sonlaensis is followed here.
Morphology
Like other members of its genus, Haotula sonlaensis is a small, elongate, near-scaleless loach built for life on the stream bed, with the erectile suborbital spine typical of the loach superfamily Cobitoidea tucked in a groove beneath the eye. FishBase records a maximum size of 2.5 in standard length, making it a genuinely small species even by stone-loach standards.
Detailed morphological description — fin ray counts, exact colour pattern, barbel arrangement — has not surfaced in the cached sources for this species. Rather than invent specifics, this profile notes only the confirmed size and the generic Schistura body plan: a slender, cylindrical-to-compressed body suited to holding position in current, with the small embedded scales and thin, exposed skin that make loaches in general sensitive to poor water quality and heavy medication.
Habitat
The species is known from Vietnam, with its type locality at Son La City in the country's mountainous northwest. FishBase describes it as demersal and tropical, living in freshwater streams typical of the region's hill and mountain drainages.
The most distinctive habitat note on record is behavioural rather than purely physical: FishBase reports the species occurring from July to October, following the receding water into caves as the wet season ends, and forming shoals there. This suggests a population that uses karst or cave-adjacent stream systems seasonally rather than one confined to open surface water year-round — a pattern documented in a handful of other Southeast Asian cave-associated fishes. No published temperature or pH readings for this species are available in the cached sources, so specific water-chemistry figures are left unstated rather than guessed; a cool-to-moderate, well-oxygenated, flowing hill-stream regime typical of Nemacheilidae is the reasonable inference, not a documented fact.
Feeding
FishBase lists the diet as larvae, insects, and ants, consistent with the family's general pattern: Haotula sonlaensis is a benthic micro-predator, picking small invertebrates and terrestrial insects that fall or wash into the stream off the bottom and among cobbles and debris.
No aquarium feeding record exists for this species specifically, but based on its diet in the wild and the pattern typical of Schistura generally, it would be expected to take small live and frozen foods — bloodworm, small crustaceans, chopped invertebrates — readily, while being slow to recognise dry flake or pellet as food, at least initially.
Mating
No courtship or spawning behaviour has been documented for Haotula sonlaensis in the sources available. Sexual dimorphism has likewise not been described for this species; nemacheilid loaches in general show little obvious external difference between the sexes outside of breeding condition, when females typically appear rounder-bodied with eggs. Rather than construct a courtship narrative from a related species, this profile leaves the point open: data on reproductive behaviour is sparse for this species.
Breeding
No breeding has been documented for Haotula sonlaensis, in captivity or otherwise. Stone and brook loaches as a group are egg-scatterers, releasing eggs over gravel and among stones in fast-flowing water with no parental care, and they are rarely bred in the home aquarium — most stay wild-caught curiosities rather than farmed or hobby-spawned fish. There is no reason to expect this species departs from that pattern, but no confirmed record exists either way, so this should be read as the general rule for the group rather than a documented fact about this species specifically.
In the aquarium
Haotula sonlaensis is not established in the aquarium trade and does not appear on the major hobbyist reference sites (Seriously Fish and Loaches Online both returned no species-specific profile). Any fish reaching hobbyists would almost certainly be a wild-caught, incidental find from Vietnamese stream collections rather than a deliberately targeted or farmed species.
For a keeper who did encounter it, the sensible approach follows the general Nemacheilidae rulebook: a small (2.5 in) benthic loach needs a tank with fine, soft substrate, smooth stones or gravel to forage among, and — given its recorded habit of retreating into caves as water recedes — plenty of dark crevices and cave-like hiding spots rather than open, brightly lit space. As with all loaches, its near-scaleless skin makes it sensitive to copper and full-strength medications, so any treatment should be conservative. Given how little is documented about this species' water chemistry, a keeper should treat it cautiously and aim for stable, clean, well-oxygenated flowing water rather than assume specifics that have not been published.
Conservation
Haotula sonlaensis has not been assessed on the IUCN Red List and is recorded here as Not Evaluated. Like many small-range Southeast Asian stream and cave-associated loaches, it is known only from a limited area around its type locality in Son La, Vietnam, and no population trend or threat assessment has been published.
Without a formal assessment, this profile does not speculate on conservation status beyond noting that stream and karst habitats in northern Vietnam face general regional pressures from agriculture, development and water extraction. A species with a narrow known range and a habit tied to seasonal cave use, as this one appears to have, would be a reasonable candidate for future assessment, but that is an observation about the general risk profile of such species, not a documented finding about this one.