Taxonomy & naming
Melanotaenia kolaensis was described by Gerald R. Allen, Renny K. Hadiaty, Peter J. Unmack and Mark V. Erdmann in 2015, in a paper in aqua, International Journal of Ichthyology (volume 21, issue 2, pages 66–108) revising the rainbowfishes of the Aru Islands and describing five new species alongside redescriptions of M. patoti and M. senckenbergianus. Eschmeyer's Catalog of Fishes treats the valid name as Melanotaenia kolaensis Allen, Hadiaty, Unmack & Erdmann, 2015; 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 radiate across New Guinea and northern and eastern Australia. M. kolaensis belongs to the Aru radiation, a set of closely related species occupying the low limestone islands that lie off the south-western coast of New Guinea. The type material was collected on Kola Island in 2013. It is distinguished from its Aru relatives chiefly by its colour pattern in life, and otherwise by a combination of meristic and morphometric characters rather than any single diagnostic trait — within Melanotaenia, the counts overlap too broadly for that.
The specific epithet kolaensis is a toponym, formed from the name of the type locality — Kola Island — with the Latin suffix -ensis, meaning 'from' or 'belonging to' that place. The generic name combines the Greek melan, black, with the Latin taenia (from Greek tainia), a stripe or band, referring to the dark midlateral stripe characteristic of many species in the genus.
Morphology
Melanotaenia kolaensis is a small, fusiform rainbowfish, reaching about 3 in standard length in males and unsexed specimens, with females smaller at around 2.5 in SL — roughly 3 in at most. The body is of normal, moderately slender proportions for the genus rather than markedly deep; the greatest body depth recorded in an adult male is about 36 percent of standard length. Like all rainbowfishes it carries the family's divided dorsal fin, a short anterior portion followed by a longer posterior one.
Meristic characters from the original description place the species firmly within Melanotaenia: dorsal-fin spines number four to six, with twelve to thirteen soft rays in the second dorsal; the anal fin bears a single spine and eighteen to twenty-one soft rays; the pectoral fins have thirteen to fourteen rays, usually thirteen. There are thirty-three to thirty-four lateral-line scales, fourteen to sixteen predorsal scales, and seventeen to twenty-three cheek scales, with sixteen to eighteen total gill rakers on the first arch.
In life the colour is understated but distinctive. The back is light blue to blue-green, and a dark blue midlateral stripe one to two scales wide runs along the body, most conspicuous on the posterior third. Below it, a white to pale-blue stripe runs along the lower caudal peduncle and forward to mid-sides. The lower body is greyish-white to pale blue, marked with paired irregular dark blue stripes above the anal fin and a large bright blue patch behind and below the pectoral-fin base. The second dorsal, anal and caudal fins carry a reddish wash.
Habitat
Melanotaenia kolaensis is endemic to Kola, the northernmost large island of the main Aru group in Maluku Province, Indonesia. It is known from only two drainages separated by about seven to eight kilometres, and the IUCN describes its distribution as restricted to these waters. The Aru Islands are low and limestone-based, and the species' habitat reflects that geology.
The type locality lies roughly eleven kilometres upstream from the sea, at a point where the main river transitions from a broad, mangrove-lined tidal brackish stream into a narrow, steep-walled limestone channel running through woodland with pure fresh water. Most specimens were taken in this freshwater limestone reach, with some found about a hundred metres beyond the navigable limit of the stream. FishBase classifies the species as freshwater and brackish, benthopelagic and tropical, consistent with a fish living near the boundary between tidal and purely fresh reaches but collected mainly in the upstream freshwater section.
The documented range is tiny — two short drainages on a single island — so the habitat is essentially the whole story: a handful of limestone creeks in lowland woodland, with no large outlying population known elsewhere. The fish was reported common where it was collected in 2013, but no long-term water-chemistry record exists for these creeks, and specific temperature, pH and hardness values for the type locality are not available in the cached sources.
Feeding
No dedicated dietary study has been published for Melanotaenia kolaensis, and species-specific feeding data are sparse. FishBase assigns it a trophic level of about 2.9, which places it among small omnivores feeding low on the food chain — consistent with the ecology of rainbowfishes generally.
By analogy with its congeners, the Kola rainbowfish is likely an opportunistic micropredator and grazer, taking small aquatic and terrestrial invertebrates — insect larvae, tiny crustaceans, and insects fallen onto the surface — plus algae and detritus scraped from submerged surfaces and the streambed. A limestone channel with woodland overhead would supply both drifting invertebrates and terrestrial insects washed in.
Without direct observation, these are reasonable inferences rather than recorded facts. What is safe to say is that this is a small, harmless fish feeding low on the food chain, with no sign of a specialised diet.
Mating
There is no published account of courtship or spawning behaviour specific to Melanotaenia kolaensis. The species has been studied essentially only from preserved type material and brief field collections, so its mating behaviour must be inferred from the well-documented patterns of the genus.
Rainbowfishes in general are egg-scattering, plant-associated spawners with no parental care. Males of most Melanotaenia court females with intense colour displays, flaring fins and flashing the body, and many species show a flickering pale 'courtship band' along the head and nape that is most vivid in the early morning when spawning activity peaks. Courtship is typically most energetic when several males compete in the presence of females.
Whether M. kolaensis follows the pattern in detail — its own display colours, its timing — is not recorded. The reddish wash in the median fins and the bright blue pectoral patch seen on live fish may figure in display, but that is conjecture; data are sparse.
Breeding
Captive or wild breeding of Melanotaenia kolaensis has not been documented. The IUCN notes that the species has potential as an aquarium fish but is not currently in the trade, and no hobbyist breeding records were located, so no first-hand account of its reproduction exists.
If it breeds like other members of the genus, it would be a continuous or near-continuous spawner under suitable conditions, with a female depositing small numbers of adhesive eggs over an extended period rather than a single large clutch. Rainbowfish eggs typically hang by fine filaments from fine-leaved plants or, in a tank, from synthetic spawning mops; the adults give no parental care and will eat their own eggs and fry. FishBase rates the species' resilience as medium, with an estimated population-doubling time of roughly 1.4 to 4.4 years — in line with the modest, steady output seen across small rainbowfishes.
All of this is extrapolated from congeners. The actual fecundity, egg size, incubation period and fry development of M. kolaensis remain unrecorded.
In the aquarium
Melanotaenia kolaensis is, in practical terms, an aquarium fish that does not yet exist in the hobby. The IUCN explicitly notes that while it has potential as an ornamental species, it is not currently in trade, and no dedicated care page could be located for it on the major rainbowfish husbandry resources. Anyone encountering it would be working without species-specific guidance.
Should it ever reach a tank, care would likely mirror that of other small to mid-sized Melanotaenia: a peaceful, active schooling fish kept in a group, given a long open swimming lane and stable, well-filtered tropical fresh water. Its limestone catchment hints that it would tolerate, and perhaps prefer, neutral to moderately alkaline, mineralised water over soft acidic conditions — but with no figures for its native creeks, that is read off the geology, not a measured requirement.
At an adult size near 3 in and with the inferred omnivorous, micropredatory diet, it would suit a community of similarly sized, gentle fishes and take standard prepared, frozen and live foods. Unless and until it is collected and bred for the hobby, though, species-specific husbandry stays data sparse, and these notes are extrapolations from its relatives.
Conservation
Melanotaenia kolaensis is assessed as Least Concern on the IUCN Red List (version 3.1), in an assessment by G.R. Allen dated 3 December 2019 and published in 2020 (citation e.T161098925A161098933). The species is known only from two drainages separated by about seven to eight kilometres on Kola Island, the northernmost large island of the main Aru group in Maluku Province, Indonesia, and it was reported to be common when collected in 2013. Its population trend is listed as unknown.
Despite its very restricted range, the assessment found no major threats to the species at the time of evaluation. A proposed oil-palm plantation on the island, which would have put the habitat at real risk, was overturned, removing the most obvious pressure on its limestone creeks. The fish is not a migrant, and it is not exploited for the aquarium trade, so collecting pressure is negligible. Together these support the Least Concern listing despite the narrow distribution.
The real concern remains the confinement to a single small island. A fish restricted to two short drainages has little buffer against future habitat disturbance, even with no major threat active now. Protecting the Kola Island freshwater catchments — and watching for renewed proposals for large-scale land conversion — is the practical way to keep it secure.