Taxonomy & naming
Melanotaenia rubrivittata was described in 2015 by Gerald R. Allen, Peter J. Unmack, and Renny K. Hadiaty in the journal Fishes of Sahul, the publication of the Australia New Guinea Fishes Association. The species is known from the Wapoga River system of Papua Province, in the Indonesian western half of New Guinea, and the original description was based on material collected there. Eschmeyer's Catalog of Fishes records the valid name as Melanotaenia rubrivittata Allen, Unmack & Hadiaty, 2015; because the species was described in Melanotaenia and remains there, no parenthetical authority is used.
The specific epithet rubrivittata is Latin for 'red-striped', from ruber (red) and vitta (band or stripe), referring to the row of fine red lines that run along the upper body — the character the describers used to separate it from the superficially similar dwarf neon rainbowfish, Melanotaenia praecox. The genus name Melanotaenia combines the Greek melas (black or dark) and the Latin taenia (a band or stripe), a reference to the dark lateral band shown by many species in the genus. Melanotaenia is the largest genus in the family Melanotaeniidae, the true rainbowfishes, which radiate across New Guinea and northern and eastern Australia.
Morphology
Melanotaenia rubrivittata is one of the smaller rainbowfishes, reaching a maximum recorded length of about 2 in standard length in males and roughly 1.5 in in females — comparable in size to the well-known dwarf neon rainbowfish. Like other members of the genus it is a laterally compressed, moderately deep-bodied fish carrying the family's divided dorsal fin, a short anterior dorsal followed by a longer posterior dorsal. Adult males are noticeably deeper-bodied than females, with body depth averaging roughly 38 percent of standard length.
The colour pattern is what sets the species apart. In life the upper two-thirds of the body is neon blue, overlaid with about five fine red stripes — one running between each row of scales — while the lower head and body shade to silvery white with a pinkish cast, and the caudal fin is red. That electric-blue ground colour and crisp red striping, which intensifies with age and in the company of other males, is what earns the fish its trade name of 'Red Laser'. Meristic counts reported in the original description include a lateral series of 32 to 33 scales, an anal fin with one spine and roughly 17 to 21 soft rays, and 12 to 14 gill rakers on the first arch.
Habitat
Melanotaenia rubrivittata is known only from the Wapoga River system of Papua Province, Indonesia — a single river drainage, which makes it a narrowly distributed species. It is a freshwater, benthopelagic fish of warm tropical waters; FishBase reports temperatures of about 27 to 29 degrees Celsius and a pH range of roughly 6.6 to 8.0 for the species.
The type series gives an unusually detailed picture of the fish's preferred waters. The type specimen came from a small, fully shaded pond about 12 metres across and averaging only 30 centimetres deep, with a bottom of soft mud and dead-leaf organic debris, formed where a tributary of the Wapoga system had flooded in the past. The species was also taken from small closed-canopy rainforest streams only two to five metres wide. In these waters it lives alongside other New Guinea fishes: the gudgeon Mogurnda wapoga, juvenile Glossolepis leggetti, the rainbowfish Melanotaenia rubripinnis, and Chilatherina alleni — small fishes sheltering in dim, vegetated, slow-moving forest water.
Feeding
Detailed dietary studies of Melanotaenia rubrivittata are not available, but its feeding ecology can be inferred from its small size, its low trophic level (estimated at about 2.9), and the habits of rainbowfishes generally. Like its relatives it is an opportunistic omnivore that forages in the upper and middle water column, taking small aquatic and terrestrial invertebrates — insect larvae, tiny crustaceans, and insects fallen onto the surface — together with algae and organic detritus from its leaf-littered forest-stream habitat.
In the aquarium the species is undemanding and accepts a wide range of foods. Hobbyist accounts describe it as an omnivore that readily takes good-quality flake and micro-pellets along with frozen and live foods such as brine shrimp and Daphnia, and note that a protein-rich, varied diet improves the males' colour. As a small, constantly active fish it does best on modest amounts several times a day rather than one large feeding.
Mating
Specific observations of courtship in Melanotaenia rubrivittata are sparse, but the species follows the well-documented pattern of the genus: rainbowfishes are egg-scattering, plant-spawning fishes in which males compete to court females with intense colour displays. Hobbyist sources report that males of this species are the more colourful sex, with somewhat extended finnage, and that their blue-and-red pattern intensifies when several males are kept together and display against one another — consistent with the competitive courtship seen across Melanotaenia.
As in related rainbowfishes, display and spawning likely concentrate in the early hours after first light, a receptive female following a displaying male into fine vegetation to release small numbers of eggs. Males show their best colour against rivals, so the species looks its best — and spawns most freely — kept as a group rather than as an isolated pair.
Breeding
Melanotaenia rubrivittata has not been the subject of detailed published breeding studies, but it is bred in captivity and tank-bred fish are widely available in the trade, indicating it is no harder to spawn than other small rainbowfishes. Hobbyist accounts describe the typical rainbowfish method: the fish are egg-scatterers, and females deposit adhesive eggs among fine-leaved plants or on synthetic spawning mops, releasing a few eggs at a time over an extended period rather than a single clutch.
Reported incubation times for the species are on the order of seven to ten days before the eggs hatch, after which the tiny fry require very small first foods such as infusoria before they can take newly hatched brine shrimp and finely crushed flake. As is the rule among rainbowfishes, the adults offer no parental care and will eat their own eggs, so breeders typically move the spawning medium or eggs to a separate rearing container. Adult colours come in slowly as the young fish mature.
In the aquarium
Melanotaenia rubrivittata is a peaceful, very active midwater schooling fish that is best kept in a group of six or more; in the trade it is regarded as hardy and easy to care for, and much of the stock offered is captive-bred. It is a restless, fast swimmer for its size and wants open swimming room, with hobbyist guidance suggesting an aquarium of around 30 US gal or more for a group. A secure, well-fitting lid is important, as rainbowfishes are accomplished jumpers.
Reported aquarium parameters are warm and near-neutral to slightly alkaline: temperatures of about 23 to 27 degrees Celsius, a pH of roughly 6.5 to 7.8, and moderate hardness, consistent with the wild range of pH 6.6 to 8.0. The species mixes well with other peaceful community fishes — other rainbowfishes, tetras, rasboras, peaceful barbs, Corydoras, and loaches — but slow or aggressive tankmates are best avoided, and because it is a small fish with a midwater predatory streak it may take very small shrimp or shrimplets. Reported lifespan is around three to five years. A note of caution on size: some retail profiles cite an adult length of four to five inches, which far exceeds the scientific maximum of under 2 in standard length and is almost certainly overstated.
Conservation
Melanotaenia rubrivittata is assessed as Least Concern (LC) on the IUCN Red List, in an assessment dated 5 December 2019. Despite its very restricted natural range — a single river drainage, the Wapoga system — the species was not judged to face an elevated extinction risk at the time of assessment, and FishBase rates it as having high resilience and low vulnerability to fishing.
Still, a species confined to one drainage in a remote part of New Guinea has little geographic buffer against future habitat change, and its small, closed-canopy forest streams and ponds are exactly the sort of environment sensitive to logging, land-use change, or altered water flow. As with many recently described New Guinea rainbowfishes, a steady presence in the hobby through tank-bred stock keeps the species going in captivity and takes collecting pressure off the wild population. Hard population data for the wild fish remain sparse.