Taxonomy & naming
Melanotaenia dumasi was described by the Dutch zoologist Max Weber in 1907, in his account of the freshwater fishes of New Guinea — 'Süsswasserfische von Neu-Guinea' — published in the monograph series Nova Guinea (volume 5, Zoology, part 2). The material came from western New Guinea, the region now within the Indonesian provinces of Papua, and the species has remained in the genus Melanotaenia, the largest genus of the rainbowfish family Melanotaeniidae. Eschmeyer's Catalog of Fishes records the valid name as Melanotaenia dumasi Weber, 1907; because it was originally described in Melanotaenia and remains there, the authority is cited without parentheses.
The genus name Melanotaenia combines the Greek melan, 'black', with the Latinised taenia, 'stripe' or 'band', a reference to the dark lateral stripe shown by many members of the genus. The specific epithet dumasi is a patronym honouring Joannes Maximiliaan Dumas (1856–1931), a feather merchant, surveyor and self-taught naturalist who collected in New Guinea over the period 1899–1917 and whose specimens reached European museums during the era when Weber and his contemporaries were first cataloguing the island's fish fauna.
Melanotaeniidae sits in the order Atheriniformes alongside the blue-eyes and silversides, with the rainbowfishes ranging across New Guinea and northern and eastern Australia. This is a large, morphologically conservative genus, and its meristic counts overlap broadly from species to species. So M. dumasi is pinned to its type material and original description rather than to any single diagnostic character you could state in a line.
Morphology
Published morphometrics for Melanotaenia dumasi are thin. FishBase lists neither a recorded maximum length nor a size at maturity, both fields left blank, so any specific measurement here would be a guess. What can be stated is the body plan it shares with the rest of the genus: Melanotaenia rainbowfishes are laterally compressed and moderately deep-bodied, with two separate dorsal fins — a short anterior dorsal followed by a longer-based posterior one — a configuration that marks out the family at a glance.
No species-specific colour and pattern description for dumasi turns up in the readily available literature, so its appearance is best treated as data sparse. It would be expected to carry the iridescent scaling and reflective sheen of the genus, and, as in its relatives, mature males are probably deeper-bodied and more intensely coloured than females. But the precise hues, the presence or strength of a lateral stripe, and the fin markings are not established in the accessible record, and are not asserted here.
For length-weight, FishBase gives only a Bayesian estimate borrowed from related species (a ≈ 0.011, b ≈ 3.04 on total length) rather than a measured fit for dumasi — one more reminder of how little direct morphological data exists for this fish.
Habitat
Melanotaenia dumasi is a freshwater fish of western New Guinea, with FishBase giving its distribution simply as Indonesia — that is, the Indonesian (western) portion of the island, historically Netherlands New Guinea. It is classed as a benthopelagic, tropical species, and the IUCN assessment categorises its habitat as inland wetlands.
Beyond that, the detail runs out. The specific lakes, rivers, or stream systems it occupies, and their measured water chemistry, are not documented in the accessible record, and are treated here as data sparse rather than filled in by analogy. New Guinea rainbowfishes occupy a wide range of lowland and upland fresh waters — clear streams, swamps, lakes — and water chemistry swings enormously across the island with local geology. Assigning dumasi a precise temperature or pH envelope from genus-level generalisation alone would be misleading.
The IUCN lists the population trend as unknown and does not quantify the number of mature individuals, which is consistent with a species that has attracted little targeted field study since its description.
Feeding
No diet study specific to Melanotaenia dumasi has been published. FishBase carries no measured trophic data and reports only an estimated trophic level of about 2.9, derived from relatives — placing it, unsurprisingly, among the lower-middle omnivores rather than as a specialised predator or a pure herbivore.
Melanotaenia rainbowfishes are generally opportunistic omnivores that feed in the upper and middle water column, taking small aquatic and terrestrial invertebrates — insect larvae, small crustaceans, insects off the surface — along with algae and plant matter. M. dumasi most likely follows the same pattern, but without gut-content analysis for the species itself, the details of its natural diet are unconfirmed and not asserted here.
And because the species is all but absent from the hobby, there is no body of captive feeding observations to fall back on, as there would be for a popular congener.
Mating
No published account describes courtship or mating in Melanotaenia dumasi, so this section is data sparse rather than reconstructed from assumption. What is known applies at the level of the genus and family.
Melanotaenia rainbowfishes are egg-scattering, plant-spawning fishes without parental care, and many spawn continuously or near-continuously under good conditions rather than to a strict season. In congeners that have been watched, dominant males stake out display areas and court females with heightened colour and fin display, often most vividly at first light, and a flickering pale 'courtship band' can flash along the head and nape of a displaying male. Whether dumasi expresses any of this, and how strongly, has not been documented.
Until someone records field or aquarium observations of this particular species, any statement about its courtship signals, pairing, or display timing would be speculation — so none is made.
Breeding
No breeding study for Melanotaenia dumasi appears in the accessible literature, and the species is not established in the hobby, so there is no captive-breeding record to summarise. Its reproductive biology is given at the genus level, with the caveat that the particulars for this species are unconfirmed.
Melanotaenia rainbowfishes are oviparous egg-scatterers. They lay small, adhesive eggs that hang by fine filaments from fine-leaved plants or, in a tank, from synthetic spawning mops. Females release a few eggs at a time over a long spawning period rather than one large clutch; the eggs hatch after roughly one to two weeks depending on temperature; and the adults give no care, readily eating their own eggs and fry. The newly hatched larvae are tiny and hang near the surface, needing very fine first foods.
Whether dumasi matches these generalisations in clutch size, egg size, and incubation is not documented, and the FishBase resilience estimate (a population doubling time of roughly 1.4 to 4.4 years, classed as medium resilience) is itself inferred from relatives rather than measured for this fish.
In the aquarium
For practical purposes, Melanotaenia dumasi is absent from the aquarium hobby. Searches of the main rainbowfish husbandry resources turn up no species-specific care or breeding profile; the guidance on offer is generic genus-level material, and what surfaces when you query the name is unrelated congeners. There is no established body of keeping experience for this fish to report.
Were it to enter the hobby, it would want what suits rainbowfishes broadly — a spacious tank with open swimming room, stable warm tropical temperatures, good filtration and water movement, and a group, since Melanotaenia are active, social shoaling fishes that show best in numbers. But the natural water chemistry of dumasi is not documented, so even these are extrapolations from the genus rather than species-specific advice, offered with that caveat.
Until wild-water parameters or captive observations exist for this species, the honest answer is that its aquarium requirements are data sparse.
Conservation
Melanotaenia dumasi was assessed for the IUCN Red List in 2019 and listed as Least Concern, the assessment dated 5 December 2019. Least Concern means that, at the time, the species was not judged to face an elevated extinction risk — a contrast with several narrowly endemic, threatened rainbowfishes of New Guinea.
The assessment still records the population trend as unknown and puts no number on mature individuals, which reflects how little direct monitoring this fish has had. Its habitat is classed as inland wetlands. FishBase rates it low in vulnerability to fishing pressure (a vulnerability index of about 10 out of 100) and medium in resilience — both consistent with a Least Concern listing, but again inferred in part rather than drawn from intensive study of dumasi.
The species is not listed under CITES and has not been evaluated under the Convention on Migratory Species. As with much of the New Guinea freshwater fauna, the likeliest future threats, should they develop, would be habitat alteration and the spread of introduced fishes. But no specific threat to dumasi is on record, and none is asserted here.