Taxonomy & naming
Melanotaenia wanoma was described in 2012 by Kadarusman, Hadiaty, Segura, Setiawibawa, Caruso and Pouyaud, in a paper titled 'Four new species of Rainbowfishes (Melanotaeniidae) from Arguni Bay, West Papua, Indonesia,' published in the French ichthyological journal Cybium (volume 36, issue 2, pages 369–382). It was one of four rainbowfishes newly described from the Arguni Bay drainages in that single study, part of a run of discoveries that keeps expanding the known rainbowfish fauna of the Bird's Neck and Bomberai region of New Guinea. The Catalog of Fishes (Eschmeyer, CAS) records the valid name as Melanotaenia wanoma Kadarusman, Segura & Pouyaud, 2012; because the species was described directly in Melanotaenia, the authority carries no parentheses.
The genus Melanotaenia is the largest in the family Melanotaeniidae, the true rainbowfishes that radiate across New Guinea and northern and eastern Australia. The Arguni Bay group to which M. wanoma belongs is allied to species already known from the Bomberai Peninsula, and the four described together in 2012 appear to be endemic to the karst-fed drainages around the bay. The epithet honours Wanoma, a village about 10 mi north of the type locality on Arguni Bay.
Morphology
Melanotaenia wanoma is a small rainbowfish, recorded to about 3 in standard length. It carries the family's typical laterally compressed body and divided dorsal fin — a short anterior dorsal followed by a longer posterior dorsal — with a body depth reported at roughly 28.7 to 32.8 percent of standard length, making it a moderately slender member of the genus rather than a deep-bodied one. Meristic counts from the original description give 4 to 6 dorsal spines and 14 to 15 dorsal soft rays, a single anal spine with 22 to 25 anal soft rays, 34 to 36 lateral scales, and 15 to 16 gill rakers.
The most useful field character is the colour of the unpaired fins. M. wanoma carries a white margin along the trailing edges of the second dorsal and the anal fin, tipped red toward the fin extremities. That white-and-red border is the diagnostic mark, and the simplest way to separate the fish from the other Arguni Bay rainbowfishes, whose meristic counts overlap broadly. As in rainbowfishes generally, the body's structural sheen and the fin colour should be strongest in displaying, well-conditioned males — though firsthand accounts of live coloration for this rarely kept species are sparse.
Habitat
The type locality is Wermura Creek, a short, clear stream on Arguni Bay in the Bomberai region of West Papua. Its course is shaped by the surrounding karst. The creek emerges from a small cave, runs for roughly 656 ft, then drops into a subterranean outlet, resurfacing about 1 mi later from a large cave within mangrove and flowing on to the sea. Where the fish was collected the stream is narrow — on the order of a metre wide — and shallow, no more than a metre deep, running clear through primary forest.
This is a limestone, cave-fed system, and the species' biology is dominated by the fact that its known range is essentially this one stream. FishBase classifies it as a tropical, benthopelagic freshwater fish. The clear water and the links to subterranean cave passages mark it out as a specialised karst habitat rather than an ordinary lowland rainforest creek, and the lower cave mouth opens close to mangrove and the bay, putting the stream at the freshwater edge of a coastal system. No broader distribution has been documented; on present knowledge the fish is a single-stream endemic.
Feeding
No detailed diet data exist for Melanotaenia wanoma, but its trophic level is estimated at about 2.9 — squarely among the omnivores that take a mix of small animal and plant material, as rainbowfishes do generally. In a clear forest stream like this one, the natural diet would run to small aquatic and terrestrial invertebrates, insect larvae and adult insects taken at or near the surface, plus algae and other plant material grazed from submerged surfaces.
The species is rarely if ever kept, so there is no body of aquarium feeding experience specific to it. By analogy with better-known relatives, expect an opportunistic mid- and upper-water-column feeder. Beyond the estimated trophic level, though, the specifics are data-sparse: any account of captive feeding is inference from the genus, not observation of M. wanoma itself.
Mating
No spawning or courtship behaviour has been recorded for Melanotaenia wanoma specifically. Across the genus, mating follows a consistent pattern. Males are colourful and competitive, staking out display areas and courting females with heightened colour and fin display, often most intense in the morning; many species flicker a pale 'courtship band' along the head as they court. Spawning is an egg-scattering act over fine vegetation, with no pairing beyond the moment of release.
Whether M. wanoma follows this template in detail is unrecorded. Its white-and-red fin margins probably feature in male display — bright fin borders usually do in rainbowfishes — but that is inference, not observation. Treat the species' reproductive behaviour as undocumented until someone watches it spawn.
Breeding
There are no published breeding records for Melanotaenia wanoma, wild or captive. Rainbowfishes of the genus are egg-scattering plant spawners: they attach small adhesive eggs by fine filaments to fine-leaved plants or spawning mops, releasing a few at a time over many days rather than one clutch, and give no parental care. Eggs hatch after roughly a week or more, depending on temperature. M. wanoma very likely shares this mode.
FishBase rates the species' resilience as medium, with an estimated population doubling time of 1.4 to 4.4 years — a figure from life-history modelling, not from observed breeding. Beyond that, fecundity, egg development and fry rearing are unknown. The fish is essentially absent from the hobby, so the practical breeding knowledge built up around popular species like M. boesemani has no counterpart here; any protocol would have to be worked out from scratch.
In the aquarium
Melanotaenia wanoma is not established in the hobby. FishBase flags it as having aquarium potential and possible fisheries interest, but aquarists don't ordinarily encounter it, and there's no settled body of husbandry experience to draw on. Anyone keeping it would be working from general rainbowfish practice, not species-specific guidance.
By analogy with its relatives, expect an active schooling fish that wants a group, a planted tank with open swimming room, and stable, well-filtered water at warm tropical temperatures. Its origin in a clear, limestone, cave-fed stream hints that it may prefer clean, well-oxygenated, neutral-to-alkaline water over soft and acidic — though the precise tolerances are unrecorded. Given the Vulnerable status and single-stream range, any aquarium population is better treated as a candidate for careful, documented conservation breeding than for casual trade.
Conservation
Melanotaenia wanoma is assessed as Vulnerable (VU) on the IUCN Red List under criterion D2. D2 covers species with a very restricted area of occupancy or very few locations, where a plausible future threat could push them to Critically Endangered or Extinct in short order — a fit for a fish known only from one short, cave-fed stream at Arguni Bay. The Australian Government's environment department has noted the Vulnerable listing in its own regulatory documentation.
The core concern is range. With the entire known population apparently confined to one stream, the fish has almost no buffer against local disturbance — habitat alteration, a shift in the karst hydrology that feeds the creek, or the arrival of non-native fishes. No large outlying population stands ready to absorb a decline. And because the fish is not widely kept, the captive-breeding safety net that backs up some threatened rainbowfishes simply isn't there. That puts the weight on protecting the wild stream and keeping accurate watch on its single population.