Taxonomy & naming
Melanotaenia patoti was originally described by the Dutch zoologist Max Weber in 1907, from material collected in the Aru Islands of the southern Moluccas, Indonesia. Because the species has at times been placed in or compared with other genera, the authority is conventionally written in parentheses — (Weber, 1907) — and Eschmeyer's Catalog of Fishes is the authority for the valid name Melanotaenia patoti. The type locality is on Trangan Island, the largest of the Aru group.
The species was poorly known for most of the twentieth century. It was redescribed in 2015 by Gerald R. Allen, Renny K. Hadiaty, Peter J. Unmack and Mark V. Erdmann in the journal aqua (International Journal of Ichthyology), in a paper treating the rainbowfishes of the Aru Islands that described five new species alongside the redescription of M. patoti. That study confirmed the species as the sole long-recognised Melanotaenia of the Aru archipelago and clarified its diagnostic features against the newly described Aru endemics.
Melanotaenia is the largest genus in the family Melanotaeniidae, the true rainbowfishes, which radiate across New Guinea and northern and eastern Australia. Meristic characters overlap broadly between species in the genus, so M. patoti is told apart as much by its colour pattern and its restricted Aru Islands range as by counts alone.
Morphology
Patoti's rainbowfish is a small, fusiform fish, reaching about 3.5 in standard length in males and around 3 in in females. Where some of its relatives are deep and diamond-shaped, this one stays elongate, though adult males deepen with age — the greatest body depth of an adult male is reported at roughly 37 percent of standard length.
The meristic features recorded in the redescription are typical of the genus: the divided dorsal fin carries 5–6 spines in the first dorsal and 11–13 soft rays in the second; the anal fin has a single spine and 20–21 soft rays; there are 15 pectoral rays, 33–34 lateral-line scales, 16–17 predorsal scales, and 12–14 cheek scales, with 16–18 total gill rakers on the first arch.
In life the body is greenish brown to bluish above, grading to silvery white on the belly, overlaid with a series of orange-red stripes running along the flanks. As in rainbowfishes generally, colour intensity is mood- and condition-dependent, brightest in displaying males. Females and juveniles are plainer, in keeping with the sexual dimorphism seen across the genus.
Habitat
Melanotaenia patoti is endemic to the Aru Islands, a low-lying archipelago in the Arafura Sea south of the New Guinea mainland, in Indonesia's Maluku province. The type locality is on Trangan Island, and the species appears to be confined to the freshwaters of this island group. That narrow range is the central fact of its biology.
It lives in creeks with slow-flowing water and soft, muddy bottoms, where aquatic plants grow thickly and the substrate is littered with fallen leaves and submerged logs. A sluggish, well-vegetated lowland creek, in other words — not a fast or rocky one. Cover and plant growth feature prominently in the recorded habitat.
FishBase reports the species as benthopelagic and tropical, occurring in warm water (around 82 °F and above) and tolerating alkaline conditions, with pH values recorded from about 8.0 upward. In-situ water-chemistry profiling across the Aru creeks is sparse, so read these figures as indicative of a warm, alkaline lowland system rather than a precise envelope.
Feeding
No detailed dietary study of Melanotaenia patoti has been published, but its feeding ecology can be inferred from its low trophic level — FishBase places it at about 2.9 — and from the habits of rainbowfishes generally. The genus comprises opportunistic omnivores that forage in the upper and middle water column, taking small aquatic and terrestrial invertebrates such as insect larvae and small crustaceans, supplemented by algae and plant material.
Its habitat — slow creeks thick with plants, leaf litter and submerged wood — supplies plenty of small invertebrate prey and grazing surfaces, which fits a generalist omnivorous diet.
In captivity, where the fish is uncommon, expect it to behave like other Melanotaenia: taking good-quality flake and small pellets along with frozen and live foods such as Daphnia, brine shrimp and bloodworm, and doing best on a varied diet with a live or frozen component to hold colour and condition. Captive feeding notes specific to this species are sparse.
Mating
Reproductive behaviour has not been documented in detail for Patoti's rainbowfish specifically, so the account here is drawn from the consistent pattern across the genus rather than from species-specific observation. Melanotaenia are egg-scattering, plant-spawning fishes with no parental care, and they tend to spawn continuously under favourable warm conditions rather than in a single seasonal pulse.
Dominant males stake out display areas and court females hard, flaring the fins and flashing the body so the orange-red striping reaches maximum saturation. A flickering pale courtship band along the head and nape is a common signal in displaying males, and the display runs strongest in the early morning.
Because males show off most in the presence of rivals, the genus as a whole colours up best when several males are kept together. The same should hold for M. patoti, though it has not been formally recorded for the species.
Breeding
Captive breeding of Melanotaenia patoti is not well documented, reflecting the species' rarity in the hobby. The expectations below follow the well-established breeding biology of the genus rather than published accounts of this species, and should be treated as indicative.
Rainbowfishes of the genus Melanotaenia are egg-scattering plant spawners. Conditioned adults deposit small, adhesive eggs that hang by fine filaments from fine-leaved vegetation such as Java moss or from synthetic spawning mops, releasing a few eggs at a time over many days rather than a single large clutch. The adults offer no care and will consume their own eggs, so breeders typically transfer the spawning medium to a separate rearing container.
At warm tropical temperatures the eggs hatch after roughly one to two weeks, and the tiny fry need very small first foods — infusoria, rotifers or commercial liquid fry food — before moving on to newly hatched brine shrimp. Growth is slow, and full adult colour comes in slower still. Breeding data specific to M. patoti are sparse; these notes are extrapolated from the genus.
In the aquarium
Patoti's rainbowfish is rare in the aquarium trade, though there is some hobbyist appetite for it — its potential import into Australia has been the subject of a draft biosecurity risk assessment, a sign of trade demand. Practical husbandry knowledge for the species is thin, so keepers fall back on the well-understood requirements of the genus.
Like other Melanotaenia, it should be an active, peaceful schooling fish, best kept in a group in a tank with a long open swimming lane and some planted cover. Its home water — warm, slow, vegetated creeks on the alkaline side — points to neutral-to-alkaline, moderately hard water and tropical temperatures around the upper 20s Celsius, with stability and good filtration counting for more than exact numbers. FishBase characterises the fish as harmless and of low fishing vulnerability.
Tankmates should be similarly sized, peaceful, and brisk enough not to lose out at feeding time. Because the species is so seldom kept, most of this is reasoned from genus-level husbandry rather than from real captive experience with M. patoti.
Conservation
Melanotaenia patoti is assessed as Least Concern (LC) on the IUCN Red List, in an assessment carried out on 3 December 2019 and published in 2020. The species carries IUCN identifier 161109984.
The Least Concern listing reflects that, although the species is endemic to the Aru Islands and therefore naturally restricted in range, it is not at present known to face threats severe enough to qualify it for a threatened category. FishBase rates its population resilience as medium, with an estimated population-doubling time of 1.4 to 4.4 years, and its fishing vulnerability as low.
Still, a fish confined to one island group has little room to absorb future pressure — habitat alteration, or the introduction of non-native fishes — so the restricted range is worth keeping in view even under a Least Concern listing. As a rarity in the trade, it puts little collecting pressure on wild stocks at present.