Taxonomy & naming
Parosphromenus rubrimontis was described by Maurice Kottelat and Heok Hee Ng in 2005. The type locality is Bukit Merah, Perak, on the Malay Peninsula, from which the specific epithet is derived: ruber (Latin, 'red') combined with mons, montis (Latin, 'mountain'), together meaning 'of the red mountain', a reference to Bukit Merah ('Red Hill' in Malay). Eschmeyer's Catalog of Fishes records the valid name as Parosphromenus rubrimontis Kottelat & Ng, 2005.
The genus Parosphromenus — the licorice gouramis — belongs to the family Osphronemidae and comprises small, stenotopic blackwater specialists distributed across the Sunda lowlands of southern Thailand, the Malay Peninsula, Sumatra, and Borneo. All members are labyrinth fishes, possessing the suprabranchial organ that allows aerial respiration. P. rubrimontis is distinguished from congeners by its fin-colour pattern: males carry turquoise outer margins on the dorsal, caudal, and anal fins separated from a red proximal zone by a black subdistal band, with pelvic fins black and iridescent blue at the basal third — a combination not exactly replicated in any close relative.
Morphology
Parosphromenus rubrimontis is a very small fish, reaching approximately 1 in standard length (FishBase) or up to 1.5 in total length (Parosphromenus Project). The body is slender and laterally compressed, typical of the genus, with a pointed snout and the rounded caudal fin characteristic of licorice gouramis. Fin-ray counts recorded from FishBase run to 11–12 dorsal spines plus 5–7 soft rays, and 13–14 anal spines plus 6–8 soft rays.
Sexual dichromatism is pronounced. Males in breeding dress show a black subdistal band in the dorsal, caudal, and anal fins, with the area proximal to that band coloured red and the outer margin turquoise or greenish-blue. The pelvic fins are black with an iridescent blue zone covering the basal third. Females and resting males are cryptic — brownish and unmarked — with colour intensifying in males only during display and breeding. This pattern of colour restricted to display contexts is typical of the genus and makes sexing non-displaying individuals challenging.
Habitat
The species inhabits peat swamp forest creeks and associated still to very slowly flowing blackwater channels in lowland Perak, Malaysia. The water is characterised by extremely low pH (the Parosphromenus Project records 3.5–4.5 at the type locality), very low conductivity (~20 µS/cm), and heavy humic staining from decomposing leaf litter and peat. Light penetration is limited; dissolved oxygen near the surface is maintained partly by the fish's ability to breathe atmospheric air via the labyrinth organ, an adaptation critical in the oxygen-poor, still conditions of peat swamp interiors.
FishBase records depths of 3–7 ft for the species, and the Parosphromenus Project notes benthopelagic habits — the fish lives close to the substrate and leaf-litter accumulations rather than in open water. Natural water temperatures in the Sunda lowlands typically range from around 75 °F to 82 °F. The original type locality at Bukit Merah has been nearly entirely destroyed by agricultural conversion; the Parosphromenus Project documents relic populations persisting in remaining fragments of peat swamp, under acute threat from continued oil-palm expansion.
Feeding
Like all licorice gouramis, P. rubrimontis is a micropredator, feeding on tiny invertebrates in the water column and on or among leaf litter: small crustaceans, zooplankton, insect larvae, and similar prey make up the natural diet. The small gape constrains prey size; only very small live or frozen foods are accepted.
In the aquarium the species requires live or small frozen foods in practice. Newly hatched brine shrimp (Artemia nauplii), micro-worms, Daphnia, Cyclops, and similar live cultures are the staples. Dry foods are generally refused or ignored. Because the fish feeds close to the substrate and is timid at the surface, food must be delivered in a way that reaches the lower water column rather than simply scattered at the top. Individual fish can be surprisingly selective and will fast if conditions or food type do not meet their requirements.
Mating
Parosphromenus rubrimontis is a cave or substrate spawner: the male selects a small enclosed space — a crevice, a hollow, the underside of a piece of driftwood or a leaf overhang — and invites the female inside for spawning. This is fundamentally different from the bubble-nest building of many other labyrinth fishes; while some species in the genus may produce a sparse cluster of bubbles on the cave ceiling to support eggs, the defining element is concealment within an enclosed cavity rather than an exposed surface nest.
Courtship is elaborate. The male displays the full brilliance of his fin colouration — the turquoise margins, black bands, and red zones becoming maximally saturated — and adopts a characteristic head-down posture toward the female. The Parosphromenus Project notes that females become pale and subdued in colouration during the breeding phase. Only a female that responds positively to the male's display and follows him into the spawning cavity will spawn; pairs that are incompatible show no interest in one another and should be separated to avoid stress.
Breeding
Spawning takes place inside the chosen cave or cavity. The female deposits eggs — clutches typically number 20–40 (Parosphromenus Project) — which are fertilised by the male and, in many Parosphromenus species, may be loosely adhered to the substrate or ceiling of the cavity. The male guards and tends the eggs; the female's involvement ends with spawning.
Successful captive breeding requires replication of the species' extreme blackwater conditions: water must be very soft and acidic (pH 4.0–5.5 is typically targeted by specialists), conductivity kept very low, and quality maintained at a high standard through careful husbandry and appropriate tannin-rich decor (Indian almond leaves, dried leaf litter, peat filtration). Spawning caves can be fashioned from small pieces of bamboo tube, coconut shell halves, or folded leaf sections. Fry are tiny on emergence and require the very smallest live foods — infusoria and rotifers — before graduating to Artemia nauplii. The Parosphromenus Project community has maintained captive populations as a conservation buffer given the precarious state of wild habitat.
In the aquarium
Parosphromenus rubrimontis is an advanced-keeper species. It is not recommended for community aquaria: it is very small, slow, and timid, and will be outcompeted by almost any other fish. Nano tanks of 5.5–10 US gal, heavily planted or leaf-littered and kept species-only or with only the smallest, most docile companions (such as pygmy rasboras or otocinclus at suitable water parameters), suit it best. The tank must be covered to prevent surface air from chilling in cooler rooms and to allow unobstructed access to atmospheric air via the labyrinth organ.
Water chemistry is non-negotiable: pristine quality, very low pH and conductivity, and warm temperature matching the peat-swamp origin. Standard tap water is unsuitable; reverse-osmosis or rain water adjusted with peat or blackwater extracts is required. Filtration should produce gentle, near-imperceptible current. This is a fish for hobbyists specifically interested in keeping and breeding Parosphromenus; its demands are high, its tolerance of deviation narrow, and its rewards — the display of a male in full colour — proportionally striking. Given the species' Endangered status and the destruction of its type locality, captive breeding carries genuine conservation value.
Conservation
Parosphromenus rubrimontis is assessed as Endangered (EN) on the IUCN Red List under criterion B1ab(iii), assessed 14 January 2019. The assessment reflects a small, severely fragmented extent of occurrence and continuing decline in habitat quality driven by conversion of peat swamp forest to oil-palm plantations and other agriculture. The Parosphromenus Project records that the original type locality at Bukit Merah had been nearly entirely destroyed at the time the species was formally described; remaining populations persist in relic habitat fragments under ongoing pressure from the same processes.
Peat swamp forests are among Southeast Asia's most threatened ecosystems, and the licorice gouramis that depend on their intact hydrological and chemical conditions are disproportionately affected. P. rubrimontis was first imported to Europe in 1984 — more than two decades before its formal scientific description — and hobbyist captive populations maintained by the Parosphromenus Project and allied aquarists represent a meaningful insurance colony for a species whose wild future is uncertain. Sourcing captive-bred stock and actively supporting breeding programmes is the primary action available to aquarists for this species.