Taxonomy & naming
Melanotaenia multiradiata was described by Gerald R. Allen, Peter J. Unmack and Renny K. Hadiaty in 2014, in a paper introducing three new rainbowfishes from the Birds Head (Vogelkop) Peninsula of West Papua Province, Indonesia, published in aqua, International Journal of Ichthyology (volume 20, number 3). Eschmeyer's Catalog of Fishes records the valid name as Melanotaenia multiradiata Allen, Unmack & Hadiaty, 2014; because the species was described in Melanotaenia, where it remains, no parenthetical authority is used.
The genus Melanotaenia is the largest in the family Melanotaeniidae, the true rainbowfishes, which range across New Guinea and northern and eastern Australia. M. multiradiata belongs to the cluster of recently described Birds Head endemics. Because coloration overlaps broadly within the genus, it is most reliably told apart from its relatives by meristic characters rather than by colour pattern. The species is tied to the Moswaren area of the peninsula, hence its English common name, the Moswaren rainbowfish.
The specific epithet multiradiata is Latin for 'many-rayed', a reference to the relatively high pectoral-fin ray count that helps distinguish the species. As with most rainbowfishes, the diagnosis rests on a combination of fin-ray and scale counts together with body proportions rather than on any single conspicuous feature.
Morphology
Melanotaenia multiradiata is a fusiform, laterally compressed rainbowfish reaching a maximum recorded length of about 5 in SL. The body is compressed and only moderately deep, with the greatest body depth of adult males falling at roughly 2.7 to 3.2 times in the standard length — a more elongate profile than the deep, diamond-shaped silhouette of some of its better-known congeners.
Meristically the species shows the divided dorsal fin typical of the genus, with the first dorsal of four to six spines and the second dorsal of one spine plus fourteen to seventeen soft rays (most often five spines anteriorly and one spine with fifteen soft rays behind). The anal fin bears one spine and twenty-three to twenty-six soft rays. The diagnostic character that gives the species its name is the comparatively high pectoral-fin ray count of fourteen to seventeen (usually fifteen or sixteen). Lateral scales number thirty-seven to thirty-eight, and total gill rakers on the first arch run sixteen to nineteen.
In life the colour is comparatively subdued: bluish-green to yellowish on the upper body, grading to white ventrally. A dark mid-lateral stripe is usually present and tends to be broader and more prominent on the posterior half of the body, while the dorsal fins carry a dark submarginal stripe set off by a pale outer margin. As across the genus, displaying and well-conditioned fish should show the most intense coloration; the original description is the main source for what the species looks like.
Habitat
Melanotaenia multiradiata is endemic to the Birds Head (Vogelkop) Peninsula of West Papua Province, Indonesia, in the Moswaren area from which it takes its common name. It is a freshwater, benthopelagic species recorded from shallow water — depths on the order of 0–7 ft — in a tropical lowland setting.
Like other Birds Head rainbowfishes, it occupies clear lowland streams and associated still waters, where rainbowfishes generally shelter among aquatic vegetation, roots, and marginal cover. Detailed water-chemistry measurements for its specific localities are not recorded in the readily available sources, so precise temperature, pH, and hardness figures for the wild habitat are data-sparse and are best inferred only loosely from the warm tropical lowland conditions typical of the region.
What stands out about the distribution is how narrow it is. Confined to a small part of the peninsula and known from few locations, M. multiradiata has the restricted range typical of many recently described New Guinea rainbowfishes — and that limited distribution is what drives its conservation assessment.
Feeding
No diet study specific to Melanotaenia multiradiata is available, and FishBase records a trophic level of about 2.9 without detailing gut contents. The species is therefore best described as a presumed opportunistic omnivore on the pattern of rainbowfishes generally, taking small aquatic and terrestrial invertebrates from the water column and surface together with algae and plant material grazed from submerged surfaces.
Insect larvae, small crustaceans, and surface-falling terrestrial insects make up the bulk of the diet in comparable Melanotaenia, supplemented by algal and detrital material. As an active, mid-water grazer it would be expected to feed steadily through the day rather than in single large meals.
Since the species is not in the hobby, there is no published aquarium feeding regime for it; any captive husbandry would have to be generalized from congeneric rainbowfishes, which do well on varied diets of quality flake and small pellets supplemented with frozen and live foods. That is inference, not a documented care record.
Mating
Direct observations of courtship in Melanotaenia multiradiata have not been published, so its mating behaviour is inferred from the well-documented patterns of the genus. Rainbowfishes are egg-scattering, plant-associated spawners in which males court females with intense colour displays — flaring the fins, saturating the body coloration, and often signalling most vividly in the early morning.
In many Melanotaenia a flickering pale 'courtship band' flashes along the head and nape of a displaying male, and males display most strongly in the presence of rivals. Whether M. multiradiata expresses this particular signal as conspicuously is not documented; its more subdued base coloration suggests displays may be correspondingly understated, but this is not confirmed.
Spawning in the genus typically takes place over fine-leaved vegetation in the hours after first light, with a receptive female following a displaying male into cover to release eggs. In the absence of species-specific data, these patterns are offered as the expected behaviour for a Melanotaenia rather than as confirmed observations for M. multiradiata.
Breeding
There is no published breeding account for Melanotaenia multiradiata. FishBase notes resilience as medium, with an estimated population doubling time of 1.4 to 4.4 years, which implies a moderate reproductive rate but says nothing about the specifics of spawning, fecundity, or development for this species.
Bred in a tank, it would likely follow the standard rainbowfish pattern: small adhesive eggs laid a few at a time over many days onto fine-leaved plants or spawning mops, hanging by fine filaments from the medium, with no parental care and a tendency for adults to eat their own eggs. Incubation in comparable Melanotaenia runs a week or more at warm temperatures, and the tiny fry need very small first foods before they can take newly hatched brine shrimp.
All of this is generalized from congeners. Because the species is recently described and not maintained in captivity, its actual reproductive biology remains essentially unrecorded, and any of the details above should be treated as expectation rather than documented fact.
In the aquarium
Melanotaenia multiradiata is not established in the aquarium hobby. FishBase lists its aquarium interest only as 'potential', and no dedicated care sheet or husbandry record for the species could be located; it is a narrowly endemic, recently described fish that has not entered the ornamental trade in any meaningful way.
Any keeping advice would therefore have to be extrapolated from the husbandry of better-known Melanotaenia: an active, peaceful, schooling fish best kept in groups with ample open swimming space, in stable, well-filtered tropical water. Given the species' size — to roughly 4.5 in — a long tank would be appropriate, as with other mid-sized rainbowfishes. These are genus-level expectations, not species-specific recommendations.
FishBase notes the species' low fishing vulnerability and harmless nature, but there is no body of hobbyist experience to draw on. For now M. multiradiata is a fish of scientific and conservation interest rather than an aquarium subject, and anyone thinking of keeping it should keep in mind how little is actually documented about what it needs.
Conservation
Melanotaenia multiradiata is assessed as Vulnerable (VU) on the IUCN Red List under criterion D2. Criterion D2 applies to species with a very restricted range — a small number of locations — that makes them susceptible to the effects of human activities or stochastic events over a short period, which is consistent with the species' narrow Birds Head Peninsula endemism.
A fish confined to a small part of a single peninsula has little buffer against localized threats: habitat degradation, changes in land or water use, or the introduction of non-native fishes into its limited range could hit a large fraction of the global population at once. The same vulnerability places several of its Vogelkop relatives under threat, and it is the central conservation concern here.
Unlike some heavily collected rainbowfishes, M. multiradiata is not subject to significant pressure from the ornamental trade, since it is essentially absent from the hobby. Its conservation outlook therefore rests on the integrity of its wild habitat rather than on collecting pressure, and continued protection of the lowland waters of the Birds Head Peninsula is the key to its persistence.