Taxonomy & naming
Melanotaenia rubrostriata was described in 1886 by Edward Pierson Ramsay and James Douglas Ogilby, in their paper 'A contribution to the knowledge of the fish-fauna of New Guinea' in the Proceedings of the Linnean Society of New South Wales. The fish was originally placed in the genus Nematocentris, as Nematocentris rubrostriatus, so the species now carries its describing authority in parentheses to mark the later transfer to Melanotaenia. The type material was collected in the 1880s from the Strickland River in what is now Papua New Guinea.
The genus Melanotaenia is the largest in the family Melanotaeniidae, the true rainbowfishes of the order Atheriniformes, a group that radiates across New Guinea and northern and eastern Australia. Within that genus M. rubrostriata sits close to the widespread M. splendida complex, and it has at times been treated as a subspecies, Melanotaenia splendida rubrostriata. It is not easily told apart from M. splendida inornata, the two separated by small differences in body depth, fin counts, and colour pattern rather than any single obvious feature. That is a recurring problem in this genus, where meristic characters overlap broadly and an identification often comes down to colour and locality. Eschmeyer's Catalog of Fishes governs the valid name used here.
Morphology
The red-striped rainbowfish is a laterally compressed, moderately deep-bodied rainbowfish. FishBase and Fishes of Australia both give a maximum size of about 5 in standard length, so it is a modest-sized member of its genus rather than a large one. Like other Melanotaenia it carries the family's divided dorsal fin — a short anterior dorsal followed by a longer posterior dorsal — set on a deep, compressed body that grows deeper with age in dominant males.
The colour pattern is the source of the common name. The base colour is an overall pale bluish-green grading to white on the lower sides, with each horizontal row of scales separated from the next by a narrow stripe running from orange to pink — the 'red stripes' of the epithet. The rear fins add a second accent: the membranes between the rays of the second dorsal and the anal fin are red. As is usual in the genus, colour intensity is mood- and condition-dependent, so a displaying or well-conditioned fish shows the stripes and red fin membranes far more vividly than a stressed or subordinate one.
Habitat
Melanotaenia rubrostriata is a freshwater, benthopelagic fish of tropical lowland New Guinea. It is widely distributed across the southern part of the island, recorded between Etna Bay in West Papua and the Central Province of Papua New Guinea. The Kikori River was long regarded as its eastern limit, but later surveys — including collections from the Sapoi River in the Lakekamu Basin — showed the range to be wider than once thought. Historic and modern collection sites span a long list of southern New Guinea waters, among them Lake Murray, the Lakekamu and Laloki rivers, the Bensbach and Aramia rivers, the Ok Tedi, the Kemp Welsh River, and localities around Timika, Etna Bay, the Aru Islands, and Daru Island. In 2005 it was recorded at 28 sites across the Fly River catchment, and Hitchcock and colleagues documented it in 2012 on Boigu and Saibai, the Australian Torres Strait islands lying close to the New Guinea coast.
Water conditions reported for the species are those of warm tropical freshwaters: FishBase gives a pH range of about 6.0 to 8.0, a hardness range of roughly 5 to 20 dH, and a depth range of 0–33 ft. That spread across river, lake, and floodplain conditions points to a generalist that tolerates a range of lowland water, which goes some way to explaining why it ranges so much more widely than the narrowly endemic rainbowfishes locked into single lake systems.
Feeding
No diet study specific to Melanotaenia rubrostriata surfaced in the available sources, so feeding here is described at the level of the genus, where habits are well established and consistent. Rainbowfishes are opportunistic omnivores that forage in the upper and middle water column, taking small aquatic and terrestrial invertebrates — insect larvae, small crustaceans, and insects from the surface — alongside algae and plant material grazed from submerged surfaces and vegetation.
In captivity the genus is undemanding at the food bowl, and the red-striped rainbowfish can be expected to follow suit. A varied diet built on good-quality flake and small pellets, supplemented with frozen and live foods such as Daphnia, brine shrimp, bloodworm, and Cyclops plus some vegetable matter, supports both condition and colour. As an active, constant grazer it does best on small amounts offered several times a day rather than a single large feeding.
Mating
Detailed courtship observations specific to M. rubrostriata are not documented in the sources at hand; data here is genus-general, and the broad pattern across Melanotaenia is well understood. The rainbowfishes are egg-scattering plant spawners with no parental care, and under good conditions they spawn continuously rather than in a single seasonal pulse. Males are social and competitive: dominant individuals stake out display areas and court females with intense colour, flaring the fins and flashing the body so that stripes and fin membranes reach maximum saturation.
A characteristic feature of courtship in many rainbowfishes is a flickering pale 'courtship band' that flashes along the head and nape of a displaying male, most vivid in the morning when spawning activity peaks. Because males display most strongly in the presence of rivals, the genus is at its most colourful when several males are kept together, and breeders typically condition groups rather than isolated pairs to bring fish into peak form. Sexual dimorphism is clear in this species: males are more brightly coloured, larger, and much deeper-bodied than females.
Breeding
Specific captive-breeding records for the red-striped rainbowfish were not confirmed in the available sources, so this account follows the well-established pattern of the genus, to which the species can reasonably be expected to conform. Melanotaenia rainbowfishes are among the more tractable egg-layers in the hobby: conditioned adults spawn over fine-leaved plants such as Java moss or over synthetic spawning mops, depositing small adhesive eggs that hang from the spawning medium by fine filaments.
Spawning is typically spread over many days, with a female releasing a few eggs daily rather than one large clutch. At warm tropical temperatures the eggs hatch after roughly one to two weeks, the incubation shortening with warmth. Adults offer no care and will eat their own eggs, so breeders move the mops or eggs to a separate rearing container. The tiny fry hang near the surface at first and need very small first foods — infusoria, rotifers, or commercial liquid fry food — before graduating to newly hatched brine shrimp and finely crushed flake. As is usual in the genus, full adult colour develops slowly over many months.
In the aquarium
Melanotaenia rubrostriata is far less common in the aquarium trade than showpiece relatives such as Boeseman's rainbowfish, and no dedicated hobbyist care profile for it surfaced in the available sources; the husbandry below therefore applies the genus's well-documented requirements. As an active, peaceful schooling fish it is best kept in a group of six or more, with a male-skewed or balanced sex ratio so that males display against one another and hold their colour. It is a strong, restless swimmer that needs a long, open swimming lane, so a roomy tank suits an active adult group.
Water chemistry should fall within the warm, moderately soft-to-moderately hard, near-neutral range reported for the wild fish — roughly pH 6 to 8 and hardness around 5 to 20 dH — at tropical temperatures. Stable conditions and good filtration matter more than hitting precise numbers, and a generalist with this wide a natural range tolerates a fair spread. A planted tank with open central swimming space, some surface movement, and bright lighting shows the orange-pink stripes and red fin membranes to best effect. Suitable tankmates are similarly sized, peaceful fishes — other rainbowfishes, larger tetras, and peaceful barbs or rasboras.
Conservation
Melanotaenia rubrostriata is assessed as Least Concern on the IUCN Red List, most recently evaluated in 2020. The listing reflects the species' wide distribution across the lowlands of southern New Guinea: rather than being confined to a single small lake basin, as several threatened rainbowfishes are, it occurs across a long series of rivers, lakes, and floodplains spanning West Papua and Papua New Guinea, with no evidence of population-level decline severe enough to warrant a higher category.
That broad range and apparent ecological flexibility are the species' best protection; a generalist spread over many catchments has a resilience the narrow endemic lacks. The same wide distribution does expose it to the general pressures on the region's freshwaters — habitat alteration, the spread of introduced species — so the sensible posture is continued monitoring across the range. The fish is secure today, but its security rests on the health of a large network of lowland waters.