Taxonomy & naming
Parosphromenus gunawani was described by Ingo Schindler and Horst Linke in 2012, in an open-access paper published in Vertebrate Zoology 62(3): 399–406. The type locality is in Jambi province, north-eastern Sumatra, Indonesia, within the drainage associated with Danau Rasau — the name by which the species was known in the aquarium hobby before its formal description. Eschmeyer's Catalog of Fishes records the valid name as Parosphromenus gunawani Schindler & Linke, 2012.
The species belongs to the family Osphronemidae and the genus Parosphromenus, a clade of small, often brilliantly coloured licorice gouramis distributed across the peat swamps and blackwater streams of the Sundaland region. Within the genus, P. gunawani has been placed in the 'bintan type' group by hobbyist and trade sources, a morphological cluster sharing broad fin proportions and certain colour features with other Sumatran and Peninsular forms.
Morphology
Adults of P. gunawani are very small, reaching a maximum of approximately 1 in standard length. The body is slender and laterally compressed, typical of the genus. Meristic counts recorded from type material are: dorsal spines 11–13; anal spines 11–12; segmented anal rays 8–10. The caudal fin is rounded, carrying a narrow bluish vertical band bounded anteriorly by a brownish patch and posteriorly by a black subdistal band — a colour configuration that helps distinguish P. gunawani from closely related Sumatran congeners.
The dorsal and anal fins of males display reddish-brown banding. A diagnostic feature noted in the original description is the absence of a blotch on the posterior portion of the dorsal fin, which separates P. gunawani from certain similar species. As in other Parosphromenus, males are more intensely coloured than females, and colour intensity varies markedly with mood, condition, and water quality. The species possesses the labyrinth organ — a suprabranchial air-breathing structure — characteristic of all members of the suborder Anabantoidei.
Habitat
Parosphromenus gunawani is known only from a single site in Jambi province, north-eastern Sumatra: a shallow peat-swamp pond with water depths of approximately 12–39.5 in. The site is densely vegetated with aquatic plants and shaded by the surrounding tree and shrub canopy, producing the heavily stained, low-light blackwater conditions characteristic of Sundaland peat swamps.
Recorded water chemistry is extremely acidic: pH 4.1, with the water temperature around 84 °F. Conductivity and dissolved oxygen are low under the shade canopy, consistent with the oxygen-depleted conditions common in intact peat-swamp habitats where the labyrinth organ — enabling direct air-breathing at the surface — provides a decisive advantage over purely gill-breathing competitors and predators. The species' entire known range covers less than 6 mi², placing it among the most geographically restricted freshwater fishes in Sumatra.
Feeding
Like other small Parosphromenus species, P. gunawani is presumed to be a micropredator in nature, taking small invertebrates — microcrustaceans, insect larvae, and other zooplankton — from the water column and leaf-litter surface in its blackwater swamp habitat. The dark, still water of peat swamps is generally nutrient-poor, so prey densities are modest and foraging behaviour is likely deliberate rather than active pursuit.
In the aquarium, licorice gouramis of this genus are known to accept small live and frozen foods readily — Artemia nauplii, Daphnia, Cyclops, micro-worms, and similar offerings — but can be reluctant to take dried foods. Patience and variety are the rule; conditioning on live foods is generally necessary to bring the fish into good colour and breeding condition. Small, frequent feedings suit the species' size and temperament better than large infrequent meals.
Mating
Parosphromenus gunawani is a cave spawner, following the reproductive strategy typical of the genus. Males establish and defend small cave sites — crevices, hollow structures, the underside of large leaves or bark, or similar enclosed spaces — from which they court females with fin displays and intensified colour. The rounded caudal fin and banded dorsal and anal fins of the male are the visual signals in these courtship interactions; displaying males spread their fins to maximum extent and present their broadside to the female.
Spawning takes place inside the cave, where the male guides or entices the receptive female into the enclosed spawning site. The pair typically spawn in an embrace within the cave, and a small number of eggs are deposited at a time — often adhering to the ceiling of the cave or overhang in a loose cluster. The male assumes primary responsibility for guarding the eggs after spawning is complete, and females may be driven away from the spawning site.
Breeding
After spawning, the male P. gunawani guards the egg clutch inside the cave, fanning the eggs to maintain oxygenation and removing any that fail to develop. Clutch sizes in the genus are small relative to open-water spawners — typically a few dozen eggs per spawning event. Incubation times in Parosphromenus species are generally several days at tropical temperatures, with the male continuing to tend the larvae through the yolk-sac stage.
Successful captive breeding requires replicating the species' blackwater chemistry as closely as practical: soft, very acidic water (pH around 4.0–5.0), minimal water movement, dim lighting, and provision of multiple small cave or tube spawning sites. Botanicals such as dried leaves (Indian almond, oak) help acidify the water and recreate the peat-stained conditions the species depends on. A species-only or carefully chosen biotope tank is strongly preferred; competition or disturbance from other fish disrupts spawning behaviour and stresses what is a physically and behaviourally fragile fish.
In the aquarium
Parosphromenus gunawani is a specialist's fish, demanding in its water-chemistry requirements and too small and retiring to coexist successfully with most community species. It is best kept in a species-dedicated nano tank — 5.5–10 US gal is sufficient for a pair or small group — heavily planted or furnished with leaf litter and small cave structures, with very gentle or near-zero water movement. A tightly fitting lid is essential: all labyrinth fishes breathe atmospheric air, and the air layer above the water must be kept warm to prevent chilling of the delicate labyrinth tissue.
Water quality requirements are non-negotiable: extremely soft, very acidic water (pH 4.0–5.0, hardness as low as possible) at around 79–84 °F. Peat filtration, RO water, and botanical additives are all useful tools. The species does not tolerate the neutral or hard water that suits most gouramis. Males may spar in confined spaces; a tank long enough to allow line-of-sight breaks, or a small group kept with multiple females, reduces aggression. Aquarists with the commitment to maintain blackwater conditions will find it a captivating and relatively undemanding captive once settled, with beautiful subtle colouration and engaging behaviour around its spawning cave.
Conservation
Parosphromenus gunawani is assessed as Critically Endangered (CR) on the IUCN Red List under criterion B2ab(iii), assessed on 12 January 2019. The listing reflects an extent of occurrence confined to a single location estimated at less than 6 mi², with an ongoing and continuing decline in the quality and extent of its peat-swamp habitat. The primary driver of decline is peat-swamp drainage and conversion for agriculture and plantation forestry — pressures that have been especially severe across Jambi province and Sumatra as a whole in recent decades.
The Parosphromenus Project, an international conservation-focused network of hobbyists and researchers, documents the species and supports captive breeding as an insurance measure against wild extinction. Hobbyist breeding programmes maintain populations in European and North American fishrooms, providing a buffer against total loss, but these captive stocks cannot substitute for the intact blackwater ecosystem the species inhabits. The narrow range, tiny area of occupancy, and continuing habitat destruction place P. gunawani among the most critically at-risk freshwater fishes in Indonesia. Acquiring only captive-bred specimens — never wild-caught — is the minimum standard for any aquarist choosing to keep the species.