Taxonomy & naming
Melanotaenia angfa was described by the Australian ichthyologist Gerald R. Allen in 1990. It belongs to the genus Melanotaenia, the largest in the family Melanotaeniidae — the true rainbowfishes — which radiate across New Guinea and northern and eastern Australia within the order Atheriniformes. Eschmeyer's Catalog of Fishes, the authority for valid names, records it as Melanotaenia angfa Allen, 1990; because it was described in Melanotaenia, where it remains, the authority carries no parentheses.
The specific epithet is an acronym rather than a Latin or Greek word: 'angfa' honours the Australia New Guinea Fishes Association (ANGFA), the hobbyist-naturalist organisation whose members did much of the work of finding, documenting, and keeping New Guinea's rainbowfishes. The genus name combines Greek 'melas' (black) with 'tainia' (band or stripe), after the dark lateral band many species in the genus carry. The fish is known in the hobby as the Yakati rainbowfish.
As with most Melanotaenia, it is told apart from its relatives more by colour and geography than by hard meristic characters, which overlap broadly across the genus. Recorded fin counts place it firmly within the genus: roughly five to seven dorsal spines, eleven to fifteen dorsal soft rays, a single anal spine, and twenty-one to twenty-six anal soft rays, set against the divided dorsal fin characteristic of the family.
Morphology
Melanotaenia angfa is a medium-sized rainbowfish reaching about 4.5 in in length (recorded as 4.5 in SL for males in Allen's New Guinea fieldwork), with females and most aquarium specimens running somewhat smaller. The body is laterally compressed and moderately deep, deepening with age in dominant males, and carries the family's two-part dorsal fin — a short anterior dorsal followed by a longer posterior one — along with a long-based anal fin.
Detailed wild colour descriptions for this species are sparse in the cached sources. It follows the genus pattern, though: mature males run more colourful and deeper-bodied than the plainer, more silvery females and juveniles. As in other rainbowfishes, displaying males deepen their colours and can flash a pale courtship band along the head and nape, while subordinate or stressed fish wash out. Captive colour tracks mood, condition, diet, and lighting.
Habitat
Melanotaenia angfa is a New Guinea endemic, recorded from the Indonesian (West Papua) side of the island around 2 to 3 degrees south. It is a hill-stream species, occurring in streams running through mountainous, rainforest-clad terrain at elevations of roughly 200 to 400 metres. These are clear, well-oxygenated waters with moderate current, shaded by overhanging forest.
The recorded water conditions match this cool upland setting: tropical but on the cooler side, around 24 to 26 degrees Celsius, with near-neutral chemistry at pH 6.5 to 7.5. It is a freshwater, benthopelagic fish — it ranges through the water column rather than hugging the bottom. That wild habitat, clean and flowing and shaded with dense marginal and submerged vegetation, is the reference point for keeping the species well: steady, oxygen-rich water matters more here than soft, acidic conditions.
Feeding
Like rainbowfishes generally, Melanotaenia angfa is an opportunistic omnivore feeding in the upper and middle water column; its assessed trophic level of about 2.9 places it among the small-invertebrate-and-algae feeders rather than strict predators. In its mountain-stream habitat the natural diet runs to small aquatic and terrestrial invertebrates — insect larvae, small crustaceans, and insects taken at or near the surface — plus algae and plant material grazed from submerged surfaces.
In the aquarium it is undemanding and takes a wide range of foods: good-quality flake and small pellets, frozen and live foods such as Daphnia, brine shrimp, and bloodworm, and some vegetable matter or spirulina-based fare. A varied diet with a real live or frozen component improves both colour and breeding condition. Being an active, constant grazer, it does best on small amounts several times a day rather than a single large feeding.
Mating
Documented spawning behaviour specific to Melanotaenia angfa is sparse in the available sources, which record only that the species reproduces by distinct pairing — that is, a male courts and pairs with a female rather than spawning in an undifferentiated mass. This is consistent with the broader genus, in which rainbowfishes are egg-scattering, plant-spawning fishes with no parental care.
In rainbowfishes of this kind, dominant males stake out display areas and court females with intense colour, flaring the fins and flashing a pale band along the head and nape; the signalling tends to peak in the early morning after first light. A receptive female follows a displaying male into fine-leaved vegetation, where the pair release a few eggs at a time. Because males show off hardest with rivals present, the species is probably at its most colourful when several males are kept together — extrapolated from close relatives, not a documented observation for M. angfa.
Breeding
Confirmed home-aquarium spawning reports for Melanotaenia angfa are scarce, and the breeding details below are inferred from the well-documented patterns of closely related Melanotaenia rather than recorded for this species — a point worth keeping in mind. Rainbowfishes of this group are continuous or near-continuous egg-scatterers: conditioned adults spawn over fine-leaved plants such as Java moss or over synthetic spawning mops, depositing small adhesive eggs that hang by fine filaments from the spawning medium.
Spawning in these relatives runs over many days, a female releasing a few eggs daily rather than one large clutch; in the mid-20s Celsius the eggs hatch after roughly a week to ten days. Adults offer no care and will eat their own eggs, so breeders move the mops or eggs to a separate rearing container. The tiny fry need very small first foods — infusoria or commercial liquid fry food — before graduating to newly hatched brine shrimp. Given the species' cool, clean-stream origins, well-oxygenated near-neutral water is the safe bet; precise figures for M. angfa itself are not documented.
In the aquarium
A peaceful, active, top-swimming schooling fish, M. angfa is best kept in a group of six or more — the group keeps individuals secure and gets the males displaying and colouring up against one another. It is a strong, restless swimmer that wants a long, open swimming lane; hobby guidance suggests a minimum of around 25 US gal for a group, with more space paying off in both activity and colour. A planted tank with open central swimming space, some surface movement, and bright lighting suits it.
Match the water to the species' cool, clean mountain-stream origins: 24 to 26 degrees Celsius, pH 6.5 to 7.5, and moderately hard water (reported in the hobby around 12 to 18 dGH), kept clean and well-oxygenated with good filtration and moderate flow. Stable conditions matter more than chasing exact numbers. Good tankmates are similarly sized, peaceful, current-tolerant species — other rainbowfishes, larger tetras, peaceful barbs, rasboras. The fish is hardy once its temperature and oxygen needs are met, and hobby sources put the lifespan at up to around a decade, though that figure is carried over from rainbowfishes generally.
Conservation
Melanotaenia angfa is assessed as Least Concern (LC) on the IUCN Red List, with the assessment dated 4 December 2019. It is not listed by CITES or CMS, and as a small, harmless freshwater fish it carries a low fishing vulnerability. The Least Concern listing means that, on current evidence, the species is not thought to be at significant risk of extinction across its known range.
Like many narrowly distributed New Guinea hill-stream fishes, though, M. angfa depends on clear, cool, forest-shaded streams — habitats sensitive to deforestation, sedimentation, and introduced fishes, the same pressures that have damaged other rainbowfish populations elsewhere in New Guinea. Its place in the aquarium hobby, and the documentation and maintenance work of associations like ANGFA, the body it is named for, offer a measure of insurance: the fish stays established in captivity independent of its wild range.