Taxonomy & naming
Parosphromenus linkei was formally described by Maurice Kottelat in 1991, based on specimens collected from small creeks approximately 1 mi north of Sukamara and from the Sungai Pudukali drainage in Kalimantan Tengah (Central Kalimantan), Indonesian Borneo. The type series was collected in 1990 by German aquarist Horst Linke and his colleague Norbert Neugebauer, and the species was named in Linke's honour. It was exported to Europe in 1991, entering the hobby almost simultaneously with its formal description — an unusually tight correspondence between scientific and hobbyist discovery.
The genus Parosphromenus belongs to the family Osphronemidae and encompasses the small, secretive licorice gouramis of Southeast Asia — roughly 20 species of peat-swamp and blackwater specialists distributed across Sumatra, Borneo, and the Malay Peninsula. Within this group, P. linkei sits near congeners such as P. opalios, with which it is syntopic at some localities. Populations from the Seruyan river drainage display a distinctly reddish colour variant — referred to in the hobby as 'spec. Seruyan' — that may represent a separate genetic lineage; hobbyists and the Parosphromenus Project both recommend maintaining this form separately to preserve its integrity. The valid name as accepted by Eschmeyer's Catalog of Fishes is Parosphromenus linkei Kottelat, 1991.
Morphology
Parosphromenus linkei is a small fish, reaching approximately 1–1.5 in standard length with elongated fin filaments extending the total length to around 2 in, and occasionally 2 in in large specimens. Like all licorice gouramis it is slim and pencil-like compared to the rounder-bodied gouramis of the genus Trichopodus, with a subtly pointed snout and large eyes suited to foraging in shadowy microhabitats.
Coloration in displaying males is the main visual draw: the flanks carry a blue iridescent sheen over a dark base, with scattered spots or blotches — the 'moonspots' of the common name — showing in reflected light. Coloration intensifies during courtship, when the male adopts a characteristic head-down posture to show off his finnage. Three or more colour forms are documented in the wild, including a silverish morph, a brownish morph, and the reddish Seruyan variant; these are held as distinct by dedicated keepers. Females are considerably plainer — a drab brownish fish without the blue iridescence — and distinguishing females among congeners is notoriously difficult without careful examination.
Habitat
The natural habitat of Parosphromenus linkei is the peat-swamp forests of Central Kalimantan, Borneo — a landscape of flooded forest, slow blackwater streams, and shallow pools underlain by deep deposits of waterlogged peat. Water in these systems is stained dark brown by humic acids and tannins leaching from decomposing vegetation; conductivity is negligible (essentially unmineralised); and pH ranges from approximately 3.0 to 6.5, with the most pristine sites acidic enough to drop to 3.0–4.0. Temperatures in the shallow swamp water run warm, typically 72–82 °F, though exposed pools can fluctuate.
This is the archetypal peat-swamp specialist habitat — extreme by any aquarium standard. The fish lives in still or near-still water beneath a forest canopy, among leaf litter, submerged roots, and accumulated debris. As a labyrinth fish, it breathes atmospheric air via its suprabranchial organ, an adaptation well suited to the warm, oxygen-depleted blackwater where gill respiration alone would be inadequate. The peat-swamp forests of Kalimantan are among the most threatened ecosystems in Southeast Asia, drained extensively for agriculture and irrigation — the dominant reason P. linkei is listed as Endangered.
Feeding
Parosphromenus linkei is a micropredator in the wild, targeting the tiny invertebrates that inhabit peat-swamp water: small crustaceans, insect larvae, mosquito larvae, and other zooplankton-scale prey. The small mouth is sized accordingly — the fish cannot tackle prey of any significant size, and it hunts with the deliberate, hovering approach typical of the genus.
In the aquarium it accepts a variety of small live and frozen foods: baby brine shrimp (Artemia nauplii), Daphnia, micro-worms, mosquito larvae, Cyclops, and similar items. Newly imported or stressed fish often refuse dried foods entirely and must be started on live offerings; once settled, some individuals will eventually accept frozen alternatives. Providing variety — rotating between different small invertebrate types — keeps fish in good condition and in breeding trim. A mature aquarium with established populations of small live organisms in the substrate and décor provides between-feeding foraging that suits the species' opportunistic hunting style.
Mating
Parosphromenus linkei is a cave spawner with temporary pair bonds and sole paternal care — a reproductive mode shared across the licorice gourami genus and entirely distinct from the open bubble-nest building of larger gouramis. The male is the architect and guardian of the spawning site; the female's role ends at egg deposition.
Courtship follows a distinctive pattern. The male positions himself in a head-down, oblique posture — almost vertical — and presents his flanks and finnage at maximum intensity to the female. This head-down display is a reliable visual cue to imminent spawning activity. The male selects or defends a small cave: a crevice in driftwood, a cavity in stacked leaf litter, a hollow bamboo section, or a purpose-made PVC or ceramic cave in the aquarium. Once a receptive female approaches, the pair investigate the cave together before spawning occurs inside it.
Breeding
Spawning takes place inside the chosen cave, typically on its ceiling. The male constructs a cluster of bubbles on the cave ceiling, and eggs are deposited among these bubbles — attached to the cave roof in a small mass — rather than left free or in an open nest. Clutch sizes vary; smaller pairs may produce only a handful of fry, while large, well-conditioned adults can produce upwards of 100 eggs. After spawning the female is driven away and the male takes sole charge of the eggs and developing fry, fanning them and maintaining the bubble mass.
Eggs hatch in approximately 24–36 hours. The fry remain in the cave under paternal supervision, becoming free-swimming and independent roughly 7–11 days after spawning. Hobbyist accounts describe carefully removing the cave with the egg mass intact to a separate rearing vessel to improve fry survival — the male alone cannot defend the clutch against tankmates in a community setting. First foods for the fry must be very fine: infusoria or rotifers initially, transitioning to Artemia nauplii as the fry grow. Water chemistry for breeding should be soft and acidic, mimicking the blackwater conditions of the natural habitat; RO water conditioned with alder cones and leaf litter is a widely used approach among specialist keepers.
In the aquarium
Parosphromenus linkei is among the most approachable species in the licorice gourami genus for aquarists willing to meet its water-chemistry requirements, and the Parosphromenus Project specifically recommends it for those new to the group. That said, 'approachable for a licorice gourami' still means soft, acidic blackwater: the fish is a peat-swamp specialist, not a generalist, and placing it in hard, alkaline tap water will produce a fish that is stressed, washed-out, and short-lived.
A species-specific or carefully selected community tank is strongly advised — this fish is too small and retiring to compete with anything assertive. The aquarium should be heavily planted or furnished with leaf litter, driftwood, mosses, and caves to give the fish structure to hide within and display against. Lighting should be subdued; a dark substrate and tannin-stained water show the iridescent blue colouring at its best. Filtration should be minimal and gentle — the species lives in near-still water, and strong currents stress it. A small sponge filter or very low-flow hang-on back provides sufficient circulation without creating flow. As a labyrinth fish it requires unobstructed access to the water surface for air breathing; the tank should be covered but with a small gap for air exchange, and the air gap between water surface and cover should be kept warm to protect the delicate suprabranchial organ from chilling. The Seruyan colour variant should be kept separate from the nominate form to prevent introgression in captivity.
Conservation
Parosphromenus linkei is assessed as Endangered (EN) on the IUCN Red List under criterion B1ab(iii), with the assessment conducted on 13 January 2019. The primary threat is wholesale destruction and drainage of peat-swamp forest in Central Kalimantan for agriculture and irrigation — one of the most severe forms of habitat loss affecting any freshwater fish in Southeast Asia. The species' area of occupancy is small and declining; peat-swamp forests that once covered vast areas of Borneo have been converted at accelerating rates, and the acidic blackwater streams and pools that P. linkei depends on disappear with the forest that creates them.
Collection for the ornamental fish trade has historically added pressure on localised populations, though this is secondary to habitat loss. The Parosphromenus Project — a hobbyist-led conservation and breeding initiative — actively promotes captive maintenance and breeding of P. linkei and its congeners as both a hedge against wild extinction and a means of reducing demand for wild-caught specimens. Hobbyists keeping this species are encouraged to source captive-bred stock, maintain accurate provenance records (particularly for the Seruyan colour variant), and participate in coordinated breeding efforts.