Taxonomy & naming
Melanotaenia pimaensis was described by the Australian ichthyologist Gerald R. Allen in 1981, and the valid name is recorded in Eschmeyer's Catalog of Fishes as Melanotaenia pimaensis Allen, 1981. Because it was described in Melanotaenia, where it remains, the authority carries no parenthesis. The species belongs to the family Melanotaeniidae — the true rainbowfishes and their blue-eye relatives — within the order Atheriniformes, and to the genus Melanotaenia, the largest in the family, whose members radiate across New Guinea and northern and eastern Australia.
The specific epithet pimaensis refers to the Pima River, the type locality, in the standard Latinised geographic form (-ensis, 'belonging to'). The genus name combines the Greek melan, 'black', and the Latin/Greek taenia (tainia), 'stripe' or 'band', a reference to the dark lateral stripe shown by many species in the group. Among the highland New Guinea rainbowfishes, M. pimaensis is one of several narrowly distributed species separated more by geography and subtle differences in colour and proportion than by sharp meristic breaks; fin-ray and scale counts overlap broadly across the genus.
Morphology
Melanotaenia pimaensis is a small rainbowfish, reaching about 4 in in standard length, with a common length nearer 2.5 in; it has the laterally compressed, moderately deep body typical of the genus. As in all Melanotaenia, the dorsal fin is divided into a short spiny anterior portion and a longer soft-rayed posterior portion. Published meristics give roughly 5 to 7 dorsal spines and 12 to 17 dorsal soft rays, with a single anal spine and 20 to 24 anal soft rays.
Colour notes for living fish are thin in the accessible literature, and this atlas won't assert a pattern that can't be traced to a reliable source. As in rainbowfishes generally, adult males of the genus tend to be deeper-bodied and more vividly coloured than females, with the brightest hues showing in displaying fish — but for M. pimaensis specifically, the livery is best treated as data-sparse rather than documented.
Habitat
Melanotaenia pimaensis is endemic to Papua New Guinea and, as currently known, to a very narrow range: the Pima River at its junction with the Tua River, in the Southern Highlands. FishBase places the species in tropical fresh water between about 6 and 8 degrees south, and describes it as benthopelagic — living and feeding through the water column near the bottom rather than strictly at the surface or substrate.
The recorded habitat is mountainous headwater streams above roughly 2625 ft elevation, set within a broad valley about a kilometre wide — cool, clear-flowing water quite different from the warm lowland lakes occupied by some better-known rainbowfishes. That tight known distribution, a single river confluence in remote highland country, also explains why firm field data on the species remain so limited.
Feeding
FishBase characterises Melanotaenia pimaensis as an egg-laying omnivore with a trophic level of about 2.9, consistent with the broadly omnivorous feeding seen across the rainbowfishes. The natural diet of upland Melanotaenia is made up of small aquatic and terrestrial invertebrates — insect larvae, small crustaceans, and insects taken from the water surface — supplemented by algae and plant material grazed from submerged surfaces.
No diet study exists for this species in the consulted sources, so the picture rests on the FishBase trophic figure and general rainbowfish biology, not on gut-content data for M. pimaensis itself. Kept in a tank — which it rarely is — it would presumably take the same varied omnivore fare as its congeners: small prepared, frozen, and live foods.
Mating
FishBase notes that Melanotaenia pimaensis shows 'distinct pairing' during reproduction, the same broad mating mode reported for many rainbowfishes, in which a male courts and spawns with a female rather than broadcasting gametes indiscriminately. As in the genus generally, this is expected to involve male display — fin-flaring and intensified colour — directed at receptive females, typically most active in the early hours after first light.
Detailed courtship observations for M. pimaensis don't appear in the accessible record. What's written here is inferred from the FishBase note and from well-documented congeners; the species-specific detail is flagged data-sparse rather than dressed up with display sequences nobody has reported for this fish.
Breeding
Melanotaenia pimaensis is an egg-laying species, and rainbowfishes as a group are egg-scattering plant spawners: the adhesive eggs are attached by fine filaments to fine-leaved vegetation or, in captivity, to spawning mops, with a female releasing a few eggs at a time over an extended period rather than a single clutch, and with no parental care.
No breeding account for M. pimaensis turned up in the consulted sources, and the species is rarely if ever bred in the hobby. The general rainbowfish pattern is the best available framework — small numbers of adhesive eggs deposited daily over many days, hatching after roughly a week or more depending on temperature, and tiny fry that need very small first foods — but read those figures as genus-level expectations, not measurements for this species. FishBase assigns the species a medium resilience, with an estimated population-doubling time of about 1.4 to 4.4 years.
In the aquarium
Melanotaenia pimaensis is a range-restricted Papua New Guinea highland endemic that is essentially absent from the aquarium trade; dedicated hobby care pages for it could not be located, and the husbandry guidance here is drawn from the general aquarium notes FishBase records for the species rather than from keepers' experience with it specifically. Those notes recommend a tank offering rock, plant, and driftwood cover, with conditions around pH 7.5, hardness near 10 dH, and a temperature of about 26 C.
Were it kept, expect it to behave like other rainbowfishes — an active, peaceful schooling fish that wants a group, a planted tank, and open water to swim in. Its cool, upland origins above 2625 ft suggest it would sit at the lower end of the tropical range rather than the warmth lowland species tolerate, and it would want stable, well-filtered, neutral to slightly alkaline water. In practice this is a fish of scientific and conservation interest, not a candidate for the home tank.
Conservation
Melanotaenia pimaensis is assessed as Least Concern (LC) on the IUCN Red List (species ID 13073). Despite its very narrow known range, the highland streams it inhabits in the Southern Highlands of Papua New Guinea are remote and relatively undisturbed, and the species faces low fishing pressure; FishBase rates its vulnerability to fishing as low and its resilience as medium.
A naturally restricted range still leaves an endemic exposed: habitat alteration, introduced fishes, or pollution in its one known catchment could hit it hard, with no large outlying population to absorb a decline. The evidence supports the Least Concern listing for now, but the species is obscure enough that monitoring data are thin — its status is better called secure-but-poorly-known than confidently abundant.