Taxonomy & naming
Melanotaenia urisa was described in 2012 by Kadarusman, Hadiaty, Segura, Setiawibawa, Caruso and Pouyaud in the journal Cybium (36(2):369–382), in a paper that introduced four new rainbowfishes from the Arguni Bay region of West Papua, Indonesia. The species was placed in Melanotaenia, the largest genus of the family Melanotaeniidae, and because it was originally described in that genus and remains there, the valid name carries no parenthetical authority: Melanotaenia urisa Kadarusman, Setiawibawa & Pouyaud, 2012. Eschmeyer's Catalog of Fishes governs the valid name.
The holotype (MZB 17715), a male of 3 in standard length, was collected from a karst spring near Sewiki Lake at Arguni Bawah in the Kaimana regency of West Papua. The specific epithet urisa refers to the village of Urisa near the type locality; the genus name combines the Greek melan (black) with the Latin taenia (stripe). The describing authors diagnosed M. urisa from congeners of the Bomberai Peninsula and the Bird's Neck region by a combination of meristic counts and body proportions rather than by any single unique character — usual for rainbowfishes, where meristics overlap broadly across the genus.
FishBase records the species under SpecCode 67379, family Melanotaeniidae (rainbowfishes and blue eyes), order Atheriniformes. The diagnostic count combination includes 4–5 dorsal spines, 12–15 dorsal soft rays, one anal spine, 21–23 anal soft rays, 36–39 lateral scales, 18–20 predorsal scales, and 17–18 gill rakers.
Morphology
Melanotaenia urisa is a small, fusiform rainbowfish, reaching about 3.5 in standard length in the largest recorded specimens (the male holotype measured 3 in SL). Like other members of the genus it has the family's characteristic divided dorsal fin — a short anterior dorsal followed by a longer posterior dorsal — set on a moderately elongate, laterally compressed body. The head is moderate in length, reported at roughly 23.7–25.2% of standard length.
Meristic characters from the original description and FishBase give 4–5 dorsal spines and 12–15 dorsal soft rays, a single anal spine with 21–23 anal soft rays, 36–39 lateral scales, 10–11 transverse scales, 18–20 predorsal scales, 13–16 cheek scales, and 17–18 gill rakers. No single count is diagnostic; the combination is what separates it from the other Arguni Bay and Bird's Neck rainbowfishes.
Life-colour information for M. urisa is data sparse. The species is recently described, rarely seen, and absent from the hobby, so the bright male display colours documented for popular congeners are not well characterised here. As in the genus, mature males are presumably deeper-bodied and more intensely coloured than the plainer, silvery females — but treat any specific colour-pattern claim for this fish cautiously.
Habitat
Habitat is what defines this fish. It is known from a single karst spring — an artesian resurgence of clear blue freshwater that wells up within a brackish, swampy coastal environment near Arguni Bay on the Bomberai Peninsula of West Papua. The type locality lies near Sewiki Lake at Arguni Bawah, Kaimana regency. Because the surrounding swamp takes in coastal saltwater, the spring's size and volume shift with season and tide.
The spring substrate is described as white sand and limestone boulders, with substantial accumulations of dead tree branches providing structure. The fish occurs syntopically with an undescribed crayfish of the genus Cherax. It is an odd address for a rainbowfish: not a lake, river, or rainforest stream, but a freshwater lens emerging from limestone in the middle of a salt-influenced wetland.
The species is freshwater and benthopelagic, in a tropical climate. FishBase rates its resilience as medium, with an estimated population doubling time of 1.4–4.4 years, and its fishing vulnerability as low (10 of 100). Its entire known range is this one spring, which is also why its conservation status is so precarious.
Feeding
No species-specific dietary study is available for Melanotaenia urisa, and its feeding ecology is data sparse. FishBase reports a trophic level of approximately 2.9 ± 0.4, which is consistent with an omnivore that takes a mix of small animal and plant material rather than a strict predator or strict herbivore.
By analogy with the genus, M. urisa likely feeds opportunistically in the water column on small aquatic and terrestrial invertebrates — insect larvae, small crustaceans, surface-falling insects — plus algae and fine plant or detrital material grazed from submerged surfaces. Its karst spring, with limestone boulders, sand, and dead wood, would offer biofilm, small invertebrates, and the wider micro-community around the syntopic Cherax crayfish.
With the species essentially absent from aquarium culture, there are no captive feeding observations. Any husbandry would follow genus norms — small prepared foods alongside live and frozen invertebrates — but that is inference, not documented practice for M. urisa.
Mating
Reproductive behaviour in Melanotaenia urisa has not been documented in detail, and this section is necessarily data sparse. No published account describes courtship, spawning sites, or mating system for the species specifically.
Melanotaenia rainbowfishes are, as a rule, egg-scattering plant-spawners with no parental care, in which males court females with colour displays — often most intense in the early morning. Across the genus, displaying males flick a pale 'courtship band' on and off. M. urisa most likely follows the same script, males displaying to receptive females over fine vegetation or other fine-textured substrate.
In its confined karst spring, with water volume swinging on the tide, the natural timing and triggers of spawning are unknown. Read anything here about its mating biology as extrapolation from close relatives, not observation of this fish.
Breeding
There is no published captive-breeding record for Melanotaenia urisa, and breeding details are data sparse. The species is Critically Endangered, single-spring endemic, and only recently of any aquarium interest, so the substantial body of hobbyist breeding knowledge that exists for popular rainbowfishes does not extend to it.
If it breeds as its congeners do, M. urisa would scatter small adhesive eggs that attach by fine filaments to fine-leaved vegetation or spawning mops, the female releasing a few at a time across an extended period rather than one clutch. The adults give no care and will eat their own eggs. In the genus, eggs hatch after roughly a week or more at warm temperatures, and the tiny fry need very small first foods.
These expectations are drawn from the genus, not from M. urisa itself. No clutch size, incubation period, or fry-rearing observation specific to this species has been reported.
In the aquarium
Melanotaenia urisa is effectively unknown in the hobby. No dedicated care page could be found, and the fish is barely present in cultivation — a consequence of its Critically Endangered status, its single-spring range, and how recently it has drawn any ornamental-trade interest at all. An Australian draft import risk assessment (DCCEEW terms of reference) lists the 'Urisa rainbowfish' among Melanotaenia under biosecurity review for importation as an ornamental fish — a sign that trade interest exists while established husbandry does not.
Any care guidance is therefore inferred conservatively from genus norms and is provisional. These rainbowfishes are typically active, peaceful schooling fishes kept in groups, in warm tropical freshwater with a long open swimming lane and good filtration. The karst-spring habitat — limestone boulders and a mineral-rich freshwater lens — points to neutral or slightly alkaline, moderately mineralised water rather than soft acidic conditions.
M. urisa is not a general hobby fish. It is a wild-restricted, threatened endemic, and any keeping belongs to managed or conservation breeding rather than casual trade. Husbandry specifics for it remain data sparse.
Conservation
Melanotaenia urisa is assessed as Critically Endangered (CR) on the IUCN Red List under criteria B1ab(iii), in an assessment by Kadarusman and G.R. Allen (assessment dated 3 December 2019, published 2020; species ID 161111673). The listing reflects the species' extremely restricted range — a single karst-spring system near Arguni Bay — together with an observed decline in the quality of that habitat.
A fish confined to one spring inside a tidally influenced brackish swamp has almost no buffer against local disturbance — no large outlying population to absorb habitat degradation, pollution, hydrological change, or an introduced competitor or predator. The artesian spring that makes the habitat distinctive also makes it fragile: its freshwater character holds only as long as the resurgence keeps overcoming the surrounding saltwater.
Emerging ornamental-trade interest, reflected in the Australian import review, adds collecting pressure to an already vulnerable population. For a species in this state, the priorities are habitat protection at the type locality and hard caution around wild collection. Broad commercial harvest of a single-spring, Critically Endangered endemic would be hard to justify.