Taxonomy & naming
Melanotaenia corona was described by the Australian ichthyologist Gerald R. Allen in 1982, in a paper titled 'Melanotaenia corona, a new species of rainbowfish from northern New Guinea.' Unusually, the description was based not on freshly collected material but on two preserved specimens that had sat unstudied in a museum for decades. Both were males, originally collected in 1911 by Dr. K. Gjellerup from the Sermowai River in what was then Dutch New Guinea (later Irian Jaya, now the Indonesian portion of Western New Guinea). Allen located the specimens in the collections of the Zoological Museum in Amsterdam and recognised them as an undescribed species.
The genus Melanotaenia is the largest in the family Melanotaeniidae, the true rainbowfishes, which radiate across New Guinea and northern and eastern Australia. Within it, M. corona is set apart less by hard counts than by a distinctive fin and pattern combination preserved in its two type specimens. Eschmeyer's Catalog of Fishes records the valid name as Melanotaenia corona Allen, 1982; because the species was described in Melanotaenia, where it remains, no parenthetical authority is used.
The entire scientific record rests on two old, faded museum specimens, so much about M. corona stays provisional. FishBase calls its biology 'not very well known,' and no live individual has turned up since the original 1911 collection — a measure of how little the freshwater fauna of interior New Guinea has been explored.
Morphology
Everything known of the corona rainbowfish's appearance comes from its two preserved male type specimens, so any description is of a faded museum fish rather than a living one. The species is a moderately elongate rainbowfish; FishBase gives a maximum recorded length of about 4 in standard length, drawn from Allen's New Guinea fish guide, though one hobby account suggests the species may exceed 4.5 in — the more conservative FishBase figure is preferred here.
The preserved males show roughly four dark longitudinal stripes on the upper body, each about one scale row wide; in life these may have been purplish, but the living colour is anyone's guess. The fins are the most diagnostic feature. The second (posterior) dorsal fin and the anal fin run long compared with other members of the genus, weighting the fish's profile toward the rear. The anal fin is dark, and the dark second dorsal carries a wide white or pale margin. Meristic counts recorded for the species include 5 dorsal spines, about 13 dorsal soft rays, 1 anal spine, and roughly 22 anal soft rays — that long anal-fin ray count being consistent with the elongate anal fin seen in the specimens.
Because the type series consists only of males, nothing can be said with confidence about the appearance of females, about how colour and finnage develop with age, or about how variable the species is across its (unknown) wild population.
Habitat
The corona rainbowfish is known only from the upper Sermowai Valley in northern Western New Guinea (former Irian Jaya), Indonesia. FishBase places the type locality at a low tropical latitude of roughly 2 to 3 degrees south. Getting there is the hard part. The original collector reached it only after travelling some three days up the lower Sermowai River by boat and then climbing several hundred metres — accounts mention a roughly 1312 ft ascent — to the waters above a waterfall.
That waterfall is central to the species' biology. Living in headwaters above a major fall, M. corona is cut off from the fish fauna of the lower river, a natural barrier that may explain how a distinctive endemic persisted there. The fish is described as freshwater and benthopelagic in a clear tropical stream, but no water-chemistry data — temperature, pH, hardness — were recorded at the type locality, so the specifics remain unknown.
Without modern fieldwork, the habitat amounts to a single point on the map: an upland tributary system above a fall in one remote valley. That extreme range restriction drives both the species' ecology and its precarious conservation outlook.
Feeding
No direct observations exist of what the corona rainbowfish eats; its diet has never been studied, and the two type specimens were preserved long before stomach-content analysis could be applied. FishBase assigns the species an estimated trophic level of about 2.9, a figure derived from models rather than from examined gut contents.
That estimate, with the feeding ecology of the genus, points to a generalist omnivore. Melanotaenia rainbowfishes typically feed in the upper and middle water column on small aquatic and terrestrial invertebrates — insect larvae, small crustaceans, and insects taken at the surface — plus algae and plant material grazed off submerged surfaces. A headwater stream above a waterfall would plausibly supply drifting terrestrial insects and aquatic larvae as the main prey.
Beyond this reasoned inference, the feeding biology of M. corona is genuinely unrecorded. It has never been kept in aquaria, so there is no captive feeding experience to draw on either; data here are sparse.
Mating
Nothing is documented about courtship or mate choice in the corona rainbowfish. The species has never been observed alive, never kept, and never bred, so there is no behavioural record at all. FishBase notes only that reproduction involves 'distinct pairing,' a general statement applied across many rainbowfishes rather than a specific observation of this species.
What can be offered is the genus pattern. In Melanotaenia, dominant males establish display areas and court females with hard colour signalling — flaring fins and, in many species, a flickering pale 'courtship band' that flashes along the head and nape, brightest in the morning. A receptive female follows a displaying male into fine vegetation, where eggs are released a few at a time. Whether M. corona shares the morning-display habit, or any of these signals, is unknown — all the more so because its living colours, the very medium of rainbowfish courtship, have never been seen.
Given the absence of any direct evidence, statements about mating in this species should be read strictly as genus-level expectation, not as observed fact.
Breeding
The corona rainbowfish has never been spawned or reared, in the wild or in captivity, and no nest, egg, or fry has ever been described. Its breeding biology is therefore entirely inferred from its relatives.
Melanotaenia rainbowfishes are egg-scattering, plant-spawning fishes with no parental care. Females release small numbers of adhesive eggs over many days rather than a single clutch, the eggs hanging by fine filaments among fine-leaved vegetation; the adults offer no care and will eat eggs and fry alike. Incubation in related species runs roughly one to two weeks depending on temperature, and the tiny fry need very small first foods. If M. corona follows this template — reasonable but unverified — it would be a continuous, plant-associated egg-scatterer.
No aspect of this has been confirmed for the corona rainbowfish itself. Clutch size, egg dimensions, incubation period, and fry development are all unrecorded; the data are sparse, and any breeding account is borrowed from the genus rather than observed in this species.
In the aquarium
Melanotaenia corona is not an aquarium fish. It has never knowingly been collected alive, never imported, and never kept or bred by aquarists; the species exists for the hobby only as a name and a story. Any fish offered for sale under this name would almost certainly be a misidentification, given that no living corona rainbowfish has been documented since 1911.
If the species were ever rediscovered and brought into culture, its care would presumably resemble that of other New Guinea rainbowfishes — an active, schooling fish needing a long tank, a group of conspecifics, and stable water — but that is genus-level guesswork, not anything learned from M. corona itself. With no wild water-chemistry data from its remote upland type locality, even the parameters one would aim for are unknown.
For now the corona rainbowfish belongs to the museum and the field notebook, not the aquarium. Its value to hobbyists and ichthyologists is as a reminder of how much of New Guinea's rainbowfish diversity remains undescribed, unkept, and barely glimpsed.
Conservation
Melanotaenia corona is assessed as Critically Endangered (Possibly Extinct) on the IUCN Red List, under criteria B2ab(iii) (assessed 2019, published 2020). The listing reflects an extreme range restriction: the species is known from a single small upland locality on the Sermowai River, above a waterfall, and from nowhere else on Earth, with an estimated area of occupancy of at most 2 mi². Confined to one tiny point, with no documented outlying populations, it has no buffer against local habitat change. The IUCN flags road construction, logging and invasive species as the threats driving inferred decline in habitat quality, and notes that targeted searches at the Sermowai in 1991, 2005, 2008, 2009, 2010 and 2012 all failed to relocate the fish.
The Critically Endangered status supersedes older information — one hobby profile still lists the species as Data Deficient, an out-of-date classification predating the current IUCN assessment. The criterion B2ab(iii) reflects a very small area of occupancy together with inferred or projected decline in habitat quality, the standard grounds on which a narrowly endemic, poorly known species is red-listed.
The deeper conservation problem is one of knowledge: because no one has documented the species alive in over a century, its actual population status, the current condition of its habitat, and even whether it still persists are unknown. Targeted survey of the upper Sermowai system above the waterfall would be the single most valuable conservation action — both to confirm the species' survival and to gather the basic ecological data that the two old type specimens could never provide.