Taxonomy & naming
Parosphromenus kishii was described in 2021 by Wentian Shi, Shujie Guo, Haryono, Yijang Hong, and Wanchange Zhang in the journal Zootaxa, in a paper diagnosing two new species of Parosphromenus from Indonesia — P. kishii from Kalimantan and P. juelinae from Bangka Island. The type locality is in Kalimantan Tengah (Central Kalimantan), Borneo. The valid name, as recorded in Eschmeyer's Catalog of Fishes, is Parosphromenus kishii Shi, Guo, Haryono, Hong & Zhang, 2021.
The genus Parosphromenus Bleeker, 1879, comprises the licorice gouramis — a group of diminutive, sexually colourful anabantoids of the Malay Peninsula, Sumatra, and Borneo that are among the most habitat-specialised freshwater fishes in Asia. All are stenotopic acid-blackwater inhabitants tightly coupled to the chemistry and structure of peat-swamp forest streams; the loss of that habitat anywhere in their tiny ranges tends to be irreversible for the local population. P. kishii is the most recently described member of this group and one of the most restricted.
Morphology
Parosphromenus kishii is a small fish even by the standards of its genus, reaching a maximum recorded standard length of 1.5 in. The body plan follows the licorice-gourami template: slender, somewhat laterally compressed, with an upturned mouth, large eyes, and the small labyrinth organ chamber behind the head that allows air-breathing. The caudal fin is rhombic — distinctly pointed or diamond-shaped — a character that distinguishes several Bornean Parosphromenus from the rounded-tailed species of the Malay Peninsula.
Colour is most conspicuous in males, which display a reddish caudal fin overlaid with a turquoise iridescent pattern. The body base colour tends to be dark, with the iridescent elements — blue-green horizontal bands or flecks — visible under good lighting. Females are plainer and brownish, retaining the caudal fin shape but lacking the vivid iridescent patterning. The full extent of colour variation across individuals and populations is not yet well documented, as the species has been formally known only since 2021.
Habitat
The species is known from a single river in Kalimantan Tengah, Borneo, running through or adjacent to oil-palm plantation land. In its natural state, Bornean peat-swamp forest produces the blackwater conditions on which all Parosphromenus depend: water filtered through deep layers of partially decomposed plant matter, stained brown to amber with humic and fulvic acids, extremely soft and acidic (pH typically 3.0–6.5), warm (72–82 °F), and low in dissolved minerals and oxygen.
The physical structure of the habitat is equally important. Parosphromenus occupy shallow, slow to nearly still channels and backwaters beneath dense riparian and forest canopy, where submerged roots, leaf litter, and overhanging vegetation provide cover and spawning surfaces. The combination of chemistry and microstructure is what the species requires, and neither element persists where plantation drainage and agrichemical inputs alter the water. The restriction of P. kishii to a single river gives it almost no spatial resilience to disturbance at that site.
Feeding
Parosphromenus kishii is a micro-predator typical of the genus. In the wild it feeds on the small invertebrates available in peat-swamp microhabitats: zooplankton, tiny crustaceans such as copepods and ostracods, insect larvae, and other invertebrates at or below the size limit its small mouth can handle. The food web of blackwater peat swamps is structured around the slow breakdown of terrestrial plant material, which supports a community of small invertebrates that these gouramis exploit.
In captivity, the species requires live or frozen micro-foods — baby brine shrimp (Artemia nauplii), micro-worms, Daphnia, copepods, and similar items — to thrive. Dry prepared foods are largely refused or ignored; keepers who rely on them report poor condition and reproductive failure. A steady supply of live food cultures is considered essential for long-term maintenance and any hope of breeding this species.
Mating
Like all Parosphromenus, P. kishii is a cave spawner: the male courts a female and induces her to enter a cave, crevice, or the underside of a broad leaf or overhang. Courtship involves intense colour display by the male, who flares his fins to maximise the surface area of the iridescent pattern visible to the female. In the confined space of a blackwater peat-swamp, where sight lines are short, close-range display intensity likely matters more than long-distance signal conspicuousness.
Once a female is induced into the spawning site, the pair align and release eggs and sperm. The eggs are typically deposited in a small adhesive cluster on the cave ceiling or a similar overhead surface, where they are held by surface tension or mild adhesion. This is not bubble-nesting: no foam or air-bubble raft is constructed. The choice of a sheltered, enclosed spawning site appears to protect the eggs both from the flow that can strip open-water spawns and from predators that would consume unguarded surface eggs.
Breeding
After spawning, the male assumes sole guardianship of the egg cluster in the cave, fanning the eggs to maintain water circulation and removing any that fail to develop. Clutch sizes in Parosphromenus are small — typically a few dozen eggs at most — consistent with the energy invested in individual offspring via paternal care. Incubation in warm, soft, acidic water takes several days; the larvae are tiny and initially feed on their yolk sacs before becoming free-swimming.
Successful captive breeding of P. kishii, as with most licorice gouramis, demands replication of the species' extreme native water chemistry: very soft, very acidic water (pH 4.0–5.5 is often cited as optimal for Parosphromenus breeding), warm temperatures, and near-still conditions with cover in the form of coconut shells, small clay tubes, or bogwood caves. Conditioning on live foods is a prerequisite. The small clutch sizes and parental-care mode mean that fry survival depends heavily on water quality and the availability of infusoria-scale first foods as the larvae transition off yolk.
In the aquarium
Parosphromenus kishii is a species for committed specialists, not the general community tank. The requirements are demanding: very soft water with negligible hardness, pH in the range of 4.0–6.0, warm temperature (75–81 °F), and virtually no water movement. Tannin-stained water produced by Indian almond leaves, peat filtration, or alder cones replicates the optical and chemical character of the natural habitat and reduces fish stress. Standard community water chemistry will suppress colour, inhibit spawning, and over time cause physiological problems in these acid-adapted fishes.
The species is best kept as a pair or small group in a dedicated species tank — a heavily planted, heavily shaded aquarium of modest volume (10–15 US gal is typical for a pair) with dense leaf-litter on the substrate, live plants including floating cover, and provision of one or more caves or crevices for spawning. Tankmates, if any, must be similarly small, peaceful, and adapted to the same extreme chemistry. EAZA guidelines and the Parosphromenus Project both document a conservation-motivated captive population strategy for the genus, and hobbyists keeping P. kishii are encouraged to connect with those networks to exchange surplus stock and maintain genetic diversity outside the wild.
Conservation
Parosphromenus kishii is assessed as Critically Endangered (CR) under IUCN criteria B2ab(iii,v), assessed in 2021 alongside the species description. The B2 criterion reflects an area of occupancy estimated below the CR threshold; the sub-criteria document ongoing decline in habitat quality (iii) and the number of mature individuals (v). With the entire known population confined to a single river running through an oil-palm plantation in Kalimantan Tengah, the species faces the full range of threats associated with industrial agriculture in Borneo: drainage of adjacent peat-swamp forest, alteration of stream hydrology, sedimentation, and contamination by agrochemicals and fertiliser runoff. Any one of these stressors alone could eliminate the species from its only known site.
Both in-situ and ex-situ conservation are considered urgent by the Parosphromenus Project and by EAZA, which has developed best-practice guidelines for the captive management of Parosphromenus as a genus. Hobbyist breeding networks — the Parosphromenus Project foremost among them — play a meaningful role in maintaining captive populations that preserve the genetic heritage of species at immediate extinction risk. Aquarists who obtain P. kishii are encouraged to treat the keeping of the species as a conservation commitment: breed them, share surplus fish through organised networks, and avoid any wild collection.