Taxonomy & naming
Melanotaenia ericrobertsi was described in 2014 by Gerald R. Allen, Peter J. Unmack and Renny K. Hadiaty in the paper 'Three new species of Rainbowfishes (Melanotaeniidae) from the Birds Head Peninsula, West Papua Province, Indonesia,' published in aqua, International Journal of Ichthyology (volume 20, issue 3, pages 139–158). The type locality lies on the Bird's Head (Vogelkop) Peninsula of West Papua Province, Indonesia. Eschmeyer's Catalog of Fishes records the valid name as Melanotaenia ericrobertsi Allen, Unmack & Hadiaty, 2014; because it was described in Melanotaenia, where it remains, the authority carries no parentheses.
The genus name Melanotaenia combines the Greek melan, 'black,' with the Latin taenia, 'stripe,' a reference to the dark lateral band characteristic of many species in the genus. The specific epithet ericrobertsi is a patronym honouring Eric Roberts, a pilot with Associated Mission Aviation in Papua Province, Indonesia, who was an aquarium enthusiast and collector and contributed to the fieldwork behind the species' discovery. The fish is known in English as the Suswa rainbowfish, after Suswa Village near its type locality.
Melanotaenia is the largest genus in the family Melanotaeniidae, the true rainbowfishes, which radiate across New Guinea and northern and eastern Australia. M. ericrobertsi belongs to the cluster of Bird's Head species. No single hard character pins it down; it is told from its relatives by adult male colour pattern and by a combination of meristic counts, since the meristics overlap broadly within the genus.
Morphology
Melanotaenia ericrobertsi reaches a recorded maximum of about 4.5 in standard length, placing it among the mid-sized members of the genus; the FishBase entry lists only a 2 in standard-length female, a type-series figure that understates the species' full size. The body is fusiform and laterally compressed, with the greatest body depth of an adult male contained roughly 2.7 to 3.1 times in the standard length. As in other Melanotaenia, the dorsal fin is divided into a short anterior portion and a longer posterior portion; in this species the origins of the first dorsal and the anal fins lie at about the same level along the body.
Meristic counts from the original description are 5 to 7 dorsal spines and 13 to 16 dorsal soft rays; a single anal spine with 23 to 27 anal soft rays; 13 to 15 pectoral rays; 37 to 39 lateral scales (usually 38); and 15 to 19 total gill rakers on the first arch. These fall within the typical Melanotaenia range, so telling it from congeners takes careful comparison rather than a single count.
The live colour of an adult male is the most distinctive feature. The body is generally mauve to pale yellowish, marked by an orange stripe running between each scale row along the side. A blackish zone covers the lower two-thirds of the caudal peduncle and the adjacent body above the last few anal rays, and a blackish patch sits immediately behind the pectoral-fin base. The pelvic and median fins are reddish, and the dorsal fins carry a narrow white margin. Females and juveniles are plainer, in keeping with the sexual dimorphism seen across the genus.
Habitat
The species is known only from the Bird's Head (Vogelkop) Peninsula of West Papua, in the vicinity of Suswa Village in the foothills of the Tamrau Mountains, about 75 mi east of the city of Sorong. The type-locality stream forms part of the extensive Kladuk River system, roughly 134 mi upstream from the Karabra Estuary on the south coast. It is a freshwater, benthopelagic fish of tropical streams, recorded from a shallow depth range of roughly 0–7 ft, in a region whose freshwater fauna remains incompletely surveyed.
At the only known locality the fish lives in a small stream about 49–98 ft wide, flowing through primary and secondary rainforest over a gravel and sand substrate with minimal aquatic vegetation. Water temperature and pH of 81–82 °F and 7.5 were recorded at the time of collection (Allen et al. 2014; IUCN assessment), placing it in warm, near-neutral water rather than the soft, acidic blackwater of some lowland New Guinea drainages.
The fish occupies the upper and middle water column of this flowing habitat among what little marginal vegetation and submerged cover the stream offers. Its restricted, single-drainage distribution is a recurring feature of the Bird's Head Melanotaenia, many of which are confined to small catchments.
Feeding
No diet study specific to Melanotaenia ericrobertsi has been published, and FishBase places it at a trophic level of about 2.9, consistent with an omnivore that leans toward small animal prey. Like rainbowfishes generally, it can be expected to feed opportunistically in the upper and middle water column on small aquatic and terrestrial invertebrates — insect larvae, tiny crustaceans, and insects taken at or near the surface — supplemented by algae and plant material grazed from submerged surfaces.
In the aquarium the genus is undemanding, and a fish of this size would be expected to accept good-quality flake and small pellets along with frozen and live foods such as Daphnia, baby brine shrimp, Cyclops, and finely chopped bloodworm. A varied diet with a live or frozen component generally improves both colour and breeding readiness in rainbowfishes. Specific feeding behaviour for this species is, however, not documented, so these notes are genus-typical rather than confirmed for M. ericrobertsi.
Mating
Direct observations of courtship in Melanotaenia ericrobertsi have not been published, and what follows is drawn from the well-documented reproductive biology of the genus rather than from this species specifically. Melanotaenia rainbowfishes are egg-scattering, plant-spawning fishes with no parental care, and they tend to be continuous or near-continuous spawners under favourable conditions rather than strictly seasonal breeders.
In rainbowfishes generally, dominant males establish display areas and court females with intense colour, flaring the fins and flashing the body so that the orange striping and reddish fins reach maximum saturation. A characteristic feature of courtship across the genus is a flickering pale 'courtship band' along the head and nape of a displaying male, most vivid in the morning hours when spawning activity peaks. Males display most strongly in the presence of rivals, so the genus is typically at its most colourful when several males are kept together. Whether M. ericrobertsi follows this pattern in every detail is not on record.
Breeding
There is no species-specific breeding account for Melanotaenia ericrobertsi in the literature — data are sparse — so its captive reproduction is best anticipated from the consistent pattern shown by other small Melanotaenia. The genus spawns over fine-leaved vegetation or synthetic spawning mops, with a female releasing small numbers of adhesive eggs that hang from the spawning medium by fine filaments, typically a few eggs each day over an extended spawning period rather than a single clutch.
In genus-typical fashion, conditioned adults at warm temperatures in the mid-to-upper 20s Celsius would be expected to spawn readily, with eggs hatching after roughly a week to ten days depending on warmth. Adults offer no care and will consume eggs and fry, so breeders generally remove the spawning medium or eggs to a separate rearing container. The minute fry hang near the surface at first and require very small first foods — infusoria, rotifers, or commercial liquid fry food — before progressing to newly hatched brine shrimp. These expectations should be read as genus-derived inference; confirmed breeding parameters for M. ericrobertsi specifically have not been documented.
In the aquarium
Melanotaenia ericrobertsi is noted as having aquarium potential, but it is not an established trade species, and dedicated species-level husbandry guidance has not been published — care notes here are inferred from the genus and should be treated accordingly. As an active, sociable rainbowfish it would suit a group of six or more in a roomy planted aquarium with open central swimming space, where a male-skewed group encourages the colour displays that bring the species to its best. At a maximum near 4.5 in it needs more length than the dwarf rainbowfishes — a tank of a metre or more suits a group.
Water conditions can follow those recorded in the wild: warm and close to neutral, around 81–82 °F and pH near 7.5, though the genus is adaptable and stable water, gentle to moderate flow, and good filtration matter more than chasing precise numbers. Bright lighting over a planted tank shows the fine orange striping and reddish fins to best effect and supports the morning display behaviour seen across the genus.
It is a peaceful, schooling fish well matched with similarly sized, robust community tankmates — other medium rainbowfishes, larger rasboras and barbs, and peaceful catfish — rather than tiny or timid companions it might outpace at feeding. Because little is recorded about this species in captivity, an aquarist keeping it should expect to manage it as a typical West Papuan rainbowfish and adjust to the fish's own response.
Conservation
Melanotaenia ericrobertsi is assessed as Least Concern (LC) on the IUCN Red List (species ID 161096432; assessed 5 December 2019, published 2020 by Allen & Kadarusman). The assessment notes that the species is restricted to a single small creek near Suswa Village but that the local human population is low and no major threats are known, and that aquarium-trade specimens are captive-bred rather than wild-caught. FishBase records the species as having high resilience, with a minimum population doubling time of under fifteen months, and as being of low vulnerability to fishing pressure. It is not listed under CITES or the CMS, and it is harmless to humans.
A Least Concern listing means the species is not presently considered at elevated risk of extinction. Even so, like many narrowly distributed Bird's Head endemics, it rests on the integrity of a limited set of drainages, and localized habitat change could hit it hard given how little ground it covers. More survey work across the peninsula's poorly documented freshwaters would sharpen the picture of its real distribution and status.
The species carries aquarium potential but is not subject to large-scale commercial collection, so trade pressure is not a significant conservation concern at present. As with rainbowfishes generally, sourcing any captive-bred stock that becomes available is the conservation-minded choice for hobbyists.