Taxonomy & naming
The Australian ichthyologist Gerald R. Allen described Kiunga bleheri in 2004, in the journal aqua (Journal of Ichthyology and Aquatic Biology), under the title "Kiunga bleheri, a new blue-eye (Pisces: Pseudomugilidae) from fresh waters of Papua New Guinea." Eschmeyer's Catalog of Fishes records the valid name as Kiunga bleheri Allen, 2004; because the species was described in its original genus, where it remains, no parenthetical authority is used. FishBase places the genus in the family Pseudomugilidae (the blue-eyes) within the order Atheriniformes.
Kiunga was itself a New Guinea discovery of the early 1980s, and it stays small — just two species, the type species K. ballochi and K. bleheri. Several structural features set it apart from the related blue-eye genus Pseudomugil: vestigial, inconspicuous dorsal fins, a rigid keel-like mid-ventral ridge running between the pelvic and anal fins, and a suite of skeletal characters. K. bleheri is told from K. ballochi by its much shorter second dorsal and anal fins, a modal difference in second-dorsal ray count, six versus five transverse body scale rows, and mostly unbranched second-dorsal and anal rays.
The genus name commemorates Kiunga, the largest settlement in the area where the type species was found. The specific epithet bleheri is a patronym honouring Heiko Bleher, the German explorer and ornamental-fish wholesaler who collected the type specimens. The fish is known by the common name Bleher's blue-eye.
Morphology
This is a very small fish. The type series ran to nine specimens of 0.5–1 in in standard length, and the maximum recorded size is about 1 in SL; aquarium-bred individuals have been illustrated at around 1 in SL. As a blue-eye it has the slender, slightly elongate body typical of the Pseudomugilidae, but Kiunga stands apart by its reduced, inconspicuous dorsal fins and a rigid, keel-like mid-ventral structure running between the pelvic and anal fins.
The colouration is subtle rather than showy. The body is mostly semi-transparent, and the second dorsal fin is faintly yellowish along its outer portion with an irregular black margin. Adult males have near-transparent fins marked with black tips on the dorsal and anal fins. That glassy look runs through the genus, and contrasts with the bolder patterns of many of its rainbowfish and blue-eye relatives.
The most reliable distinctions from the only congener, K. ballochi, are meristic and proportional: shorter second dorsal and anal fins, a different modal second-dorsal ray count, six rather than five transverse body scale rows, and second-dorsal and anal rays that are mostly unbranched. Detailed life-history and growth data are sparse.
Habitat
Endemic to Papua New Guinea, K. bleheri is known only from a few small creeks crossed by the Kiunga–Konkonda Road, roughly 6–7 mi west of the town of Kiunga in the Western Province, within the Upper Fly River system. Heiko Bleher collected the type material in 1994 and 2003, and reportedly first encountered the fish in 1991 at Tare Creek, about 7 mi north of Kiunga on the Konkonda Road. The range is essentially a single locality.
These are small, shallow, slow-flowing forest creeks and forest-fringed pools — water bodies on the order of 16 ft wide and 3 ft deep — at an elevation of about 262 ft (give or take 66 ft). The type locality was a forest-fringed pool along the Konkonda Road with no aquatic vegetation. Daytime temperatures run 75–81 °F. The water is near-neutral to slightly acidic, pH measurements spanning roughly 5.7 to 7.8 across the known sites; the type locality registered pH 6.0. What stands out is how soft and mineral-poor it is — conductivity below 30 µS/cm, and as little as about 10 µS/cm at the type locality.
Warm, soft, near-neutral, low-conductivity water in shaded lowland forest creeks: that is the narrow niche, and the pinpoint range is the central fact of the species' biology.
Feeding
No one has recorded what K. bleheri eats in the wild, so what follows is drawn from the feeding ecology of blue-eyes and rainbowfishes generally. These small fishes are omnivores: algae, small terrestrial insects such as ants that fall onto the water, aquatic insect larvae, and small crustaceans. Many have villiform teeth suited to scraping algae from hard surfaces, and FishBase places the genus at an estimated trophic level of about 3.2.
A small, schooling, midwater-to-surface fish that frequents quieter stream sections near vegetation and snags is well placed to pick invertebrate prey from the water column and surface film while grazing aufwuchs. Beyond that, dietary data are sparse, and any captive feeding guidance is extrapolated from related blue-eyes rather than direct field observation.
Mating
Direct accounts of courtship in K. bleheri are limited, but the genus follows the broad blue-eye pattern. The fish school and occupy midwater-to-surface zones near vegetation and submerged snags in the quieter parts of their creeks. Dominant males intensify their colour at first light and defend a chosen display feature — across blue-eyes and rainbowfishes, morning is the peak period for display and spawning.
The male's modest fin markings — black tips on the otherwise near-transparent dorsal and anal fins, the faintly yellow-edged second dorsal — are presumably the signals used in display, flickered at rivals and prospective mates in the early light. Pairing and spawning behaviour for this particular species are not well documented, and the finer points of mate choice remain data-sparse.
Breeding
Breeding biology specific to K. bleheri is poorly documented. By analogy with other blue-eyes and rainbowfishes, it is most likely an egg-depositing, plant-associated spawner that attaches small adhesive eggs to fine-leaved vegetation, mosses, or fine roots near the surface, releasing eggs over an extended period rather than in a single clutch, with no parental care.
Figured aquarium-bred specimens of around 1 in SL show the species has been spawned in captivity, but published rearing details are scarce. Given the soft, low-conductivity, warm, near-neutral water of its native creeks, reproduction should succeed under correspondingly soft, gently acidic conditions at temperatures in the mid-20s Celsius. Clutch sizes, incubation periods, and fry-rearing requirements are not reliably established and are best treated as data-sparse rather than estimated.
In the aquarium
This is a rarely seen aquarium fish, of interest mainly to specialist keepers of blue-eyes and New Guinea natives rather than the general hobby. A tiny schooling surface-and-midwater species, it wants a good-sized group in a quiet, well-planted tank with open water near the surface and structure — fine-leaved plants, snags — to school around, mirroring its forest-creek origins.
Water chemistry is the husbandry hurdle. Its creeks are very soft and mineral-poor (conductivity below 30 µS/cm in the wild), near-neutral to slightly acidic at pH roughly 5.7 to 7.8, and warm at about 75–81 °F. Reproducing water that low in conductivity is the real challenge of keeping the species. A peaceful blue-eye this small pairs only with similarly small, gentle tankmates, and it suits experienced aquarists prepared to manage soft water. Because the species is Critically Endangered with a pinpoint wild range, any aquarium stock should be captive-bred rather than wild-collected.
Conservation
Kiunga bleheri is assessed as Critically Endangered (CR) on the IUCN Red List under criteria B1ab(iii). The assessment was carried out on 6 December 2019, published in 2020 (Allen, Hammer & Unmack), and carried through to the current 2025-2 version of the Red List. The listing reflects an effectively single-locality range in the Upper Fly River system near Kiunga, where the fish is known only from a few small creeks along the Kiunga–Konkonda Road.
Confined to so tiny an area, the species has almost no resilience to local disturbance. Degrade those few forest creeks — road works, logging, pollution, a shift in hydrology — and the entire known global population is hit at once. There is no large outlying population to buffer a decline. FishBase notes the species is not evaluated under CITES or CMS, and rates its fishing vulnerability low; it is harmless to humans and of negligible commercial interest beyond a small specialist aquarium following.
Given that precarious status, the most useful thing aquarists can do is maintain and propagate captive-bred lines rather than draw on the wild population, and support conservation of the forest creeks west of Kiunga on which the species entirely depends.