Taxonomy & naming
Melanotaenia maylandi was described by the Australian ichthyologist Gerald R. Allen in 1983, among the steady stream of New Guinea rainbowfishes he named through the late twentieth century. The species belongs to Melanotaenia, the largest genus in the family Melanotaeniidae — the true rainbowfishes of the order Atheriniformes, which radiate across New Guinea and northern and eastern Australia. Eschmeyer's Catalog of Fishes records the valid name as Melanotaenia maylandi Allen, 1983; because the species was described in Melanotaenia, where it remains, no parenthetical authority is used.
The specific epithet honours Hans-Joachim Mayland (1928–2004), the German aquarist, ichthyological writer, and underwater photographer whose books and photographs did much to popularise rainbowfishes and other aquarium fishes in the European hobby. The genus name combines the Greek melas, 'black,' with the Latinised taenia, 'band' or 'stripe,' a reference to the dark mid-lateral band common across the genus — though in M. maylandi that marking is reduced to a diffuse, bluish, blotch-punctuated line rather than a hard stripe. Within Melanotaenia the species is regarded as close to the widespread Melanotaenia affinis of the northern New Guinea drainages, a relationship that informs what little is inferred about its breeding behaviour.
Morphology
Mayland's rainbowfish is a moderately slender, laterally compressed rainbowfish. FishBase gives a maximum recorded length of about 3.5 in standard length, based on Allen's material; some hobby sources report considerably larger fish — to roughly 5 in — but in the absence of measured voucher data the FishBase figure is treated here as the authority and the larger claim noted only as unconfirmed. Like all members of the genus it carries the family's divided dorsal fin, a short anterior portion followed by a longer posterior one, with the fins set against a deep-bodied profile that becomes more pronounced in mature males.
The colour pattern, as described from adult males, is understated by the standards of the showy Vogelkop rainbowfishes. The upper body and back are olive-green to brownish, fading to a silvery-white lower body and belly. A diffuse bluish band runs along the mid-flank, broken into a series of blotches rather than forming a continuous line, and fine narrow stripes follow the horizontal scale rows. Meristic counts reported by Allen fall within the normal generic range: dorsal spines 5–7, dorsal soft rays 16–21, a single anal spine, and 24–29 anal soft rays. As in rainbowfishes generally, displayed colour shifts with mood and condition, so a live fish shows more than a preserved one ever will.
Habitat
The known range of Melanotaenia maylandi is exceptionally small. The species has been recorded only from a single narrow creek roughly 1–2 mi from Danau Bira (Lake Holmes), within the lower Mamberamo river system of West Papua (formerly Irian Jaya), Indonesia. The creek lies in hilly terrain at about 1476 ft elevation, surrounded by dense, shadowing lowland-to-foothill rainforest, with a rocky streambed.
The Mamberamo basin is one of the largest and least-disturbed river systems in New Guinea and a centre of high freshwater biodiversity, but M. maylandi itself is documented from only this one locality. That pinpoint distribution — one small, shaded, rocky creek above a lake — is the central fact of its ecology, and the reason collectors and the aquarium trade so rarely encounter it. The canopy overhead keeps the water shaded and cooler than open lowland habitats. Detailed in-situ water chemistry has not been widely published; reported aquarium-preference figures (see below) are the best available proxy and should be read as captive recommendations rather than measured field data — habitat data here is sparse.
Feeding
In keeping with the genus, Mayland's rainbowfish is an omnivore with a low trophic level (FishBase estimates roughly 2.9), feeding on a mix of small invertebrates and plant or algal material taken from the water column and from submerged surfaces. No detailed gut-content study specific to this species appears in the literature, so the dietary picture is inferred from close relatives and from observed aquarium behaviour rather than from field data.
In captivity the species is reported to be an undemanding feeder that takes both vegetable and meaty foods readily. A balanced regime of a good herbivore/omnivore dry food supplemented with live or frozen items — brine shrimp, insect larvae, and similar small invertebrates — is recommended by hobbyists to maintain condition and colour. As with rainbowfishes generally, frequent small feedings suit an active grazer better than a single large meal.
Mating
Direct observations of courtship in Melanotaenia maylandi are scarce; the species is rare in the hobby and was, as of the available sources, believed not to have been bred in the aquarium. What is described is therefore largely inferred from its close relative Melanotaenia affinis and from the consistent reproductive pattern of the genus.
Rainbowfishes are egg-layers that form distinct pairs during spawning (FishBase notes 'distinct pairing' for this species), with displaying males intensifying colour to court females, typically most actively in the early morning hours. Spawning is a plant-associated, egg-depositing affair rather than a nest-building one, with eggs released a few at a time over an extended period. In the absence of confirmed captive spawning of M. maylandi specifically, these statements should be read as the expected pattern for the genus rather than as documented behaviour for this species.
Breeding
As of the sources consulted, Mayland's rainbowfish was believed not yet to have been bred in aquaria, so the breeding account here is by analogy to the closely related Melanotaenia affinis and to rainbowfishes in general — breeding data for this species is sparse and largely presumptive.
The expected method follows the genus: conditioned adults deposit small, adhesive eggs onto fine-leaved plants such as Java moss or onto synthetic spawning mops, the eggs hanging by fine filaments from the medium. Because rainbowfishes offer no parental care and will eat their own spawn, breeders would harvest the mops or eggs to a separate rearing container. Newly hatched fry are very small and hang near the surface at first, requiring tiny first foods — infusoria or a comparable liquid fry food — before graduating to newly hatched brine shrimp and finely crushed flake. Growth and the development of adult colour are gradual. None of these specifics has been confirmed for M. maylandi; they describe the husbandry that would be attempted given the species' affinities.
In the aquarium
Mayland's rainbowfish is rare in the hobby — not because it is difficult to keep, but because it is hard to collect and export from its single remote habitat. Where it has been maintained, it is described as a peaceful community fish that is not demanding once settled. As an active, schooling rainbowfish it is best kept in a group, with open swimming space and a tank long enough to suit a restless mid-water swimmer.
Reported aquarium preferences are slightly alkaline water around pH 7.2, moderate hardness (about 10 dGH), and a temperature near 79 °F, with subdued or shaded lighting in the spirit of its rainforest creek — floating plants are a simple way to soften it. Rocks, driftwood, and plant cover give the fish the shelter and broken sightlines it favours, much like the rocky, canopy-shaded stream it comes from. Keep tankmates similarly sized and peaceful. Given the species' rarity and threatened wild status, any specimens in the trade are best treated as a conservation-sensitive holding rather than a casual community addition.
Conservation
Melanotaenia maylandi is assessed as Vulnerable (VU) on the IUCN Red List, listed under criterion D2 in an assessment dated 5 December 2019 (IUCN species ID 13066). Criterion D2 applies to species whose populations are restricted to a very small area or number of locations such that a single plausible threat could drive them to Critically Endangered or Extinct in a short time — an exact fit for a fish known from one small creek. An older listing that treated the species as 'Lower Risk / least concern' has been superseded by this 2019 reassessment.
The species' vulnerability stems directly from its pinpoint range rather than from any documented mass collection. With a single known locality, the fish has no outlying population to buffer against local disturbance: a change to that one creek — sedimentation, water diversion, deforestation of the shading canopy, or the introduction of non-native fishes — could affect the entire known population at once. The wider Mamberamo valley has at times been targeted for large-scale hydroelectric development; a major dam scheme floated in the 1990s was shelved during the Indonesian financial crisis, but the basin's standing as a development frontier is reason enough to keep an eye on a fish this narrowly endemic. The species is not listed on CITES or the CMS.