Taxonomy & naming
Parosphromenus bintan was described by Maurice Kottelat and Peter K. L. Ng in 1998, in a paper published in Ichthyological Exploration of Freshwaters (vol. 8, no. 3, pp. 263–272) titled 'Parosphromenus bintan, a new osphronemid fish from Bintan and Bangka islands, Indonesia, with redescription of P. deissneri.' The type locality is Bintan Island at kilometre 45 of the road network (1°06′40.1″N, 104°30′09.8″E), in what is now the Riau Archipelago province of Indonesia. GBIF records the valid combination as Parosphromenus bintan Kottelat & Ng, 1998.
The species belongs to the genus Parosphromenus, the licorice gouramis, a compact assemblage of small labyrinth fishes in the family Osphronemidae. The original description included a redescription of the morphologically similar Parosphromenus deissneri, explicitly demarcating P. bintan from it on the basis of fin-ray counts and colour pattern details — a distinction that the aquarium trade has frequently ignored, and commercial fish sold as P. deissneri may include P. bintan or undescribed forms. The Parosphromenus Project notes that the true distribution of P. bintan remains incompletely understood because of the existence of unnamed similar round-tail forms across Sumatra and Borneo.
Within Parosphromenus, P. bintan belongs to the group of species characterised by a rounded caudal fin without a terminal filament — sometimes called the 'round-tail' assemblage — and by the distinctive 'head-down' courtship posture. The specific epithet bintan is a toponym referring to Bintan Island, one of the two known localities from which the species was originally described.
Morphology
Parosphromenus bintan is an extremely small fish, reaching a maximum of approximately 1 in standard length according to FishBase; overall length including the caudal fin may approach 1.5 in. The body is slender and slightly laterally compressed, with the elongated form typical of the genus. The caudal fin is rounded without a terminal filament, which distinguishes the species from the filament-tailed forms in the genus. Dorsal-fin formula is XI–XIII spines plus 5–7 soft rays (total 17–20 rays); anal fin XI–XIII spines plus 8–10 soft rays (total 19–22 rays), as recorded in the Parosphromenus Project's morphometric summary.
Sexual dimorphism in colour is pronounced. Males in full breeding condition are remarkable: the dorsal, anal, and caudal fins are patterned in concentric bands — a white outer margin, then a blue-green iridescent band, then a dark black subdistal zone, with the caudal fin centre tinged dirty red-black. Pelvic fins are vivid blue with white to blue-white filaments at the tips. The body is dark, with the iridescent fin colouration providing nearly all the visual impact at peak display. Females and non-displaying males are cryptically pale beige to brownish, with the fin banding suppressed. Females in nuptial condition lighten to a pale, near-translucent beige; they cannot be reliably distinguished from females of other round-tail Parosphromenus species by colour alone, requiring fin-ray counts for certain identification. As a labyrinth fish, the species possesses the suprabranchial labyrinth organ that permits aerial respiration, a critical adaptation to the oxygen-depleted waters it inhabits.
Habitat
Parosphromenus bintan is endemic to two islands in the Indonesian archipelago: Bintan Island in the Riau Archipelago and Bangka Island off the eastern coast of Sumatra (Palembang Province). Both support the peat swamp forests characteristic of lowland Sundaland, and the species is a stenotypic specialist of these habitats — it is not found in open rivers, clearwater streams, or lakes.
Peat swamp waters are defined by their extreme chemistry. Organic matter accumulating over millennia releases humic and fulvic acids that stain the water dark brown or near-black and drive pH to levels very rarely encountered in freshwater fish habitats. Field measurements recorded by the Parosphromenus Project from Bintan and Bangka localities give pH 4.8, GH 0, KH 1, and temperature 77 °F — water barely distinguishable in composition from weak tea. Seriously Fish documents the species' tolerated range as pH 3.0–6.5, though breeding is most reliably achieved at the lower end of that spectrum, with temperatures between 22 and 82 °F. Dissolved oxygen in peat swamps is low, which is why the labyrinth organ is so important: the fish can supplement gill-breathing with direct atmospheric air intake at the surface.
Within these swamps the species occupies slow to standing water among submerged leaf litter, root tangles, and the debris accumulated at the base of peat-swamp trees. The habitat is among the most threatened freshwater ecosystems in Southeast Asia, and both Bintan and Bangka have experienced significant land-use pressure.
Feeding
Parosphromenus bintan is a micropredator that feeds on small aquatic invertebrates in the wild — microcrustaceans, insect larvae, and other diminutive fauna present in the peat-swamp leaf litter and water column. Its small mouth limits it to correspondingly small prey, and the species hunts slowly and deliberately rather than pursuing active prey at speed.
In captivity the diet should mirror this scale. Live and frozen small foods give the best results: newly hatched brine shrimp nauplii, Moina, Daphnia, micro-worms, and mosquito larvae are all documented as accepted foods. Seriously Fish lists Artemia, Daphnia, mosquito larvae, and similar microorganisms as appropriate. Dry prepared foods may be accepted by some individuals but should not be the dietary foundation; fish maintained on flake alone typically show poor colour, reduced activity, and reduced breeding readiness. Multiple small feedings per day are preferable to one large meal, consistent with the species' small stomach volume and natural feeding mode.
Mating
Parosphromenus bintan is a cave spawner, the reproductive mode shared across the Parosphromenus genus. Courtship in this species is characterised by a distinctive 'head-down' posture in which the displaying male tilts forward, dropping the head below the level of the body, while spreading and vibrating the patterned unpaired fins to maximum effect. This head-down display is documented by Seriously Fish as characteristic of the P. bintan species group and is one of the behavioural markers that distinguishes it from other Parosphromenus assemblages.
The male selects a cave or enclosed space — a narrow tube, a crevice under a leaf, an upturned coconut shell, or a terracotta cave — and performs his displays at the entrance and interior. A receptive female is drawn into the cave through the male's courtship. Water chemistry plays a decisive role in initiating breeding behaviour: as in other Parosphromenus, pH well below 6.0 is typically required before the pair will enter spawning condition, regardless of temperature or food availability. In the very soft, acidic blackwater that defines the species' natural habitat, these conditions are met by default; replicating them in captivity is the central challenge of breeding.
Breeding
Spawning takes place inside the cave, with the pair performing repeated embraces during which eggs are deposited in small batches on the cave ceiling or walls. Seriously Fish notes that some males construct a rudimentary bubble nest — described by the Parosphromenus Project as a moderately developed foam nest that is sometimes rudimentary — suggesting variation among individuals or populations in the extent to which a bubble structure accompanies the cave deposition. The core mode, however, is cave/substrate spawning with eggs placed in an enclosed space, not open-water bubble nesting.
After spawning the male takes on brood-guarding duties, remaining at or inside the cave to tend the eggs. Incubation runs approximately 24–36 hours according to Seriously Fish. The larvae hatch with yolk sacs attached and begin active swimming around four to six days post-hatch; the male collects fallen or displaced fry and returns them to the nest for three to five days before they become fully free-swimming. The female, meanwhile, defends the surrounding territory. Clutch sizes are typical for the genus — small, reflecting the fish's body dimensions. First foods for free-swimming fry must be infusoria-scale: Paramecium and rotifers initially, transitioning to newly hatched brine shrimp nauplii. Maintaining the correct water chemistry through the entire rearing period is non-negotiable; any increase in pH or conductivity typically results in fry mortality.
In the aquarium
Parosphromenus bintan is a specialist fish suited only to aquarists who can reliably maintain very soft, acidic, blackwater conditions. The water parameters documented at the type locality — pH around 4.8, GH 0, KH 1 — represent ideal conditions; an aquarium pH of 4.0–6.5 with near-zero hardness and very low conductivity is the target range. Reverse-osmosis or rainwater is essential; ordinary tap water of even moderate hardness is unsuitable and will suppress colour, prevent spawning, and shorten lifespan. Conditioning with catappa (Indian almond) leaves, peat filtration, or dried botanicals provides tannins and the humic acid chemistry that replicates the natural environment.
Filtration must be extremely gentle — the species is adapted to virtually still water and cannot tolerate currents from standard power filters. A small air-driven sponge filter or box filter is appropriate. Temperatures should be held between 22 and 82 °F. A dedicated species tank is strongly recommended: competition from more vigorous species suppresses display behaviour and can prevent feeding. Other small Parosphromenus or comparably sized, comparably demanding blackwater species (small rasboras adapted to soft acidic water) are the most compatible tank-mates. The tank must be tightly covered — licorice gouramis must be able to breathe atmospheric air at the surface, but will jump if startled, and the warm humid air space under the lid also matters for labyrinth organ development in fry.
Caves are essential furnishings: narrow PVC or bamboo tubes, coconut half-shells, or smooth-bottomed terracotta caves placed horizontally. Dense planting with floating leaves, a dark substrate, and minimal water movement completes a setup in which males will display at full intensity. Wild P. bintan is rarely available in the trade, and commercial fish labelled as P. deissneri may represent this species. Sourcing from hobbyist breeders familiar with the species' identity — and ideally participating in the Parosphromenus Project's conservation breeding programme — is strongly recommended both for fish quality and for supporting accurate record-keeping of captive populations.
Conservation
Parosphromenus bintan is assessed as Vulnerable (VU) on the IUCN Red List, with the assessment recorded as 13 January 2019 under criterion B1ab(iii)+2ab(iii). The criterion reflects the species' restricted area of occupancy and extent of occurrence, combined with continuing decline in the quality of its peat-swamp habitat. Being confined entirely to two islands — Bintan in the Riau Archipelago and Bangka off the Sumatra coast — the species has no buffer in the form of a large mainland population; anything that damages the peat swamp ecosystems on those islands directly threatens the entire species.
Both islands have experienced substantial land-use change. Peat swamp forests across Sundaland have been converted at large scale for oil-palm and pulpwood plantations, drained by canal networks, and degraded or destroyed by agricultural fires. The Parosphromenus Project rates the species as under high extinction risk if it is truly confined to those two islands, and notes that confusion with unnamed similar forms across Sumatra and Borneo means the true distribution and therefore the true level of threat remains incompletely resolved. The trade-identification problem compounds this: fish sold commercially as P. deissneri may include P. bintan, creating a demand that could incentivise undocumented wild collection.
The Parosphromenus Project runs conservation breeding programmes for the genus and maintains P. bintan in captive-held populations. Hobbyists who keep the species are encouraged to record provenance carefully and to breed from verified stock, contributing to the captive safety-net that the Project coordinates. Acquiring specimens from participating breeders rather than from unverified commercial sources is the most practical conservation contribution available to individual aquarists.