Taxonomy & naming
Pseudohomaloptera leonardi was first described by Sunder Lal Hora in 1941, originally placed in the broad genus Homaloptera — hence the parentheses around the authority. The species subsequently appeared in the literature under the combination Balitoropsis leonardi as generic limits were debated and revised, and both older names persist in older references and some trade literature. The Catalog of Fishes (Eschmeyer, CAS) — the accepted authority for valid names — now places it in Pseudohomaloptera, a genus that sits within the family Balitoridae, the hillstream loaches of South and Southeast Asia.
The genus Pseudohomaloptera can be confused with close relatives, and P. leonardi itself is frequently misidentified as P. sexmaculata in the trade and in older records. The two are distinguished by pectoral-fin ray counts: P. leonardi has 6 simple plus 11 branched pectoral rays, whereas P. sexmaculata has 2 simple plus 12–14 branched rays. This count is the most reliable character when specimens lack full colouration or are juveniles. Collectors and importers do not always verify the count, so confirming identity from a reliable reference source before purchase is worthwhile.
Morphology
Like all hillstream loaches, P. leonardi is dorsoventrally flattened — the body is wide and low in cross-section, with pectoral and pelvic fins that are broad and horizontally splayed to press the fish against the substrate. In fast current, the combined ventral surface of fins and belly acts as a suction pad, allowing the fish to hold station on bare rock while water roars overhead. The head is depressed, the eyes positioned dorsolaterally, and the mouth inferior — positioned underneath the snout as a scraping tool for rasping biofilm and aufwuchs from rock surfaces.
Maximum recorded length is 2.5 in standard length (SL). The body is cream to pale olive overlaid with an irregular pattern of brown spots and blotches that provide camouflage against the speckled rock and gravel of its native streambeds — the markings that give it the "spotted" part of its common name. The skin is largely unscaled, or very finely scaled; this near-nakedness, common across balitorid hillstream loaches, has real consequences for medication and disease management in captivity.
Habitat
Pseudohomaloptera leonardi is native to fast, clear, oxygen-saturated hill streams and headwaters across the Malay Peninsula, the Chao Phraya drainage of Thailand, and the upper Mekong basin. These are high-gradient systems — rocky, turbulent channels where water moves powerfully over bedrock, boulders, cobble and gravel and dissolves high concentrations of oxygen in the process. Temperatures in upland Asian hill streams are moderate to distinctly cool, typically in the range of 64–79 °F; water chemistry is soft and weakly acidic to neutral (pH 6.0–7.5).
This habitat is characterised by what it lacks as much as what it contains: no silt, no standing organic matter, no warm-water stagnation, no fine sediment to coat the rock. The rock surfaces in such streams support a dense, thin layer of biofilm — algae, diatoms and periphyton — that is continuously grazed by rheophilic (current-loving) fishes including this species. Removing P. leonardi from that environment and placing it in a warm, still, bare tank is the single most common cause of its death in captivity.
Feeding
Pseudohomaloptera leonardi is an aufwuchs and biofilm grazer. In the wild it rasps algae, diatoms and the thin organic layer that coats submerged rock in fast, clean streams, supplementing this with small invertebrates — insect larvae, tiny crustaceans and any other appropriately-sized animal matter it encounters while working the rockface. This diet is low in caloric density but available continuously across vast areas of rock surface.
In the aquarium, the fish's survival hinges on whether there is enough biofilm to sustain it between supplementary feeds. A bare or newly-set-up tank, however attractive its rockscape, provides nothing to graze on, and the fish starves quietly in plain sight. An established tank of six months or more, with algae and biofilm coating the rocks, is the baseline. On top of that, keepers should offer small sinking foods — algae wafers, Spirulina-based tablets, and blanched greens such as courgette or spinach — as well as frozen or live small invertebrates: Daphnia, Artemia nauplii and bloodworm are all accepted. It is not a flake-eater and should not be expected to compete at the surface.
Mating
External sexing of P. leonardi is difficult and no reliable dimorphic characters are documented in the literature. Ripe females may be noticeably fuller-bodied when in breeding condition, but even this is inconsistent and hard to assess in a reclusive, camouflaged fish that rarely holds still. In keeping with most hillstream balitorids, there is no detailed account of mating behaviour in this species observed in captivity.
In nature, breeding is inferred to follow seasonal cues — changes in water level, temperature and flow associated with the monsoon cycle in its hill-stream habitat. The reproductive cues that trigger ripening are almost certainly tied to the hydrological and temperature fluctuations of those mountain drainages, conditions that are extremely difficult to replicate in a home aquarium. No spawning of this species in captivity has been recorded in the literature available.
Breeding
Pseudohomaloptera leonardi has not been bred in home aquaria as far as the available literature records. It is presumed to be an egg-scatterer: like other hillstream balitorids, ripe fish would deposit small eggs among stones or gravel in fast-flowing water, with no parental care following fertilisation. In related genera such as Sewellia, a small number of mature, long-established river-style aquaria have produced eggs and fry under high-flow, cool, well-oxygenated conditions — but even in those better-documented genera, success is exceptional rather than routine.
The honest picture for this species is that it is rarely or never bred by hobbyists, and stock in the trade is wild-collected from its native hill streams. Anyone hoping to breed it should provide the maximum possible simulation of its natural conditions — strong flow, cool temperature (64–72 °F), a heavily matured rocky substrate, and in season a lowering of water level followed by a gradual rise to mimic the monsoon pulse — and should treat any resulting eggs or fry as an unexpected bonus rather than a planned outcome. Patience and excellent water quality are the prerequisites; success, if it comes, is likely to be accidental before it is intentional.
In the aquarium
The Spotted Lizard Loach is a specialist's fish, and it fails in community tanks not through aggression but through incompatibility of conditions. It needs cool (64–79 °F), highly oxygenated water with powerful circulation — a turnover rate of 10–15 times the tank volume per hour is the working target, achieved by oversizing the filtration rather than by directing powerhead jets that disturb the fish on the rocks. The minimum footprint for a small group is a tank of roughly 80 × 12 in floor area; long, shallow tanks with maximum surface area are far preferable to tall, small-footprint designs. The substrate and internal hardscape should be river rocks, cobbles and slate arranged to create patches of varying current speed and numerous crevices.
Before the fish is introduced, the tank must be mature — ideally six months or more — so that algae and biofilm have colonised the rock surfaces. This is not optional; it is what the fish eats. A group of four or more is recommended: P. leonardi is not aggressive but appears to be more settled and more active in conspecific company, the fish hopping and crawling across the rockscape in their distinctive lizard-like gait. Because the skin is near-scaleless, the species absorbs medications rapidly and is sensitive to copper-based treatments and to standard-dose medication; any treatment should be at half dose at most, using products safe for sensitive scaleless fish, and copper must be avoided entirely. The fish is not compatible with warm-water community species; tankmates, if any, should share its preference for cool, fast, well-oxygenated water.
Conservation
Pseudohomaloptera leonardi is assessed as Least Concern on the IUCN Red List (2022 assessment). Its range spans several major drainages — the upper Mekong, the Chao Phraya system and the rivers of the Malay Peninsula — and it has not been found to be in decline at the population level. The breadth of its distribution across multiple river systems in different countries provides some insurance against localised events.
Nonetheless, the species is a hill-stream specialist, and hill-stream habitats across Southeast Asia face persistent and growing pressure: logging and agricultural conversion increase sedimentation and raise water temperatures in formerly clear, shaded streams; dam construction alters flow regimes and blocks seasonal movements; and water abstraction can reduce the torrential flows that such fishes require. Wild collection for the aquarium trade supplies current demand, and while the species does not appear to be commercially over-exploited, ongoing monitoring of collection pressure in the Malay Peninsula and Mekong headwaters would be prudent as hillstream loaches grow in popularity among specialist keepers.