Taxonomy & naming
Melanotaenia kamaka was described by Gerald R. Allen and Samuel J. Renyaan in 1996, in a paper treating three new rainbowfishes from the Triton Lakes of Irian Jaya (now West Papua), published in the journal aqua, Journal of Ichthyology and Aquatic Biology. The type series came from the Triton Lakes themselves, with the holotype and paratypes — fifteen paratypes measuring 1.5–2.5 in standard length — collected in June 1995. Eschmeyer's Catalog of Fishes records the valid name as Melanotaenia kamaka Allen & Renyaan, 1996; because the species was described in Melanotaenia, where it remains, no parenthetical authority applies.
The specific epithet kamaka comes from the local Triton Bay name for the type locality, Lake Kamakawaiar (Lake Kamaka), the largest of the three main Triton Lakes. Melanotaenia joins the Greek melanos, 'black or dark', with tainia, 'band or stripe' — a nod to the dark lateral band common across the genus. M. kamaka belongs to the large radiation of New Guinea rainbowfishes within the family Melanotaeniidae. Like its Triton Lakes congeners, it is set apart from relatives more by geography and colour than by hard meristic characters, which overlap broadly across the genus.
Morphology
The Kamaka rainbowfish is a small, fusiform-to-moderately-deep-bodied, laterally compressed rainbowfish. FishBase records a maximum of about 2.5 in standard length, and the type series ranged from 1.5–2.5 in SL; wild fish are usually under 2.5 in, though aquarium specimens are reported to reach a little larger, on the order of 3 in. Like other Melanotaenia it carries the family's divided dorsal fin — a short anterior dorsal followed by a longer posterior dorsal — with meristics reported as four to six dorsal spines, ten to thirteen dorsal soft rays, one anal spine, and nineteen to twenty-two anal soft rays.
The colour is understated. There are no strong two-tone or banded patterns here, just a metallic sheen. Males run deeper-bodied and more intensely coloured, developing richer metallic tones as they mature and display, while females and juveniles stay plainer. That restrained, reflective colouration is the species' draw in the hobby — a quiet shimmer that shifts with the light rather than saturated reds and blues.
Habitat
Melanotaenia kamaka is endemic to the Triton Lakes of West Papua, Indonesia — a cluster of three main lakes plus several smaller ones, set just inland from Triton Bay on the southern coast, immediately east of the Bomberai Peninsula and roughly 31 mi east of the seaport of Kaimana. The type locality, Lake Kamakawaiar (Lake Kamaka), is the largest of the group. The lakes lie in a basin surrounded by high limestone hills, and the karstic catchment gives the water a hard, alkaline character. FishBase classes the species as freshwater and benthopelagic, occupying shallow water at depths of roughly 0–7 ft.
Water measured at the type locality when the fish were collected was warm and distinctly alkaline: about 84 °F, pH 8.0, and conductivity around 220 µS/cm — a limestone-fed signature. What defines this fish is the narrowness of that range. Its wild distribution is effectively one small lake system, so it has nowhere else to occur, and that shapes both its ecology and any read on its vulnerability.
Feeding
Like rainbowfishes generally, the Kamaka rainbowfish is an opportunistic omnivore, feeding in the upper and middle water column. Its natural diet is taken to comprise small aquatic and terrestrial invertebrates together with plant matter, and it carries the fine villiform teeth typical of the genus, suited to grazing and to seizing small prey. FishBase places it at a trophic level of about 2.9, consistent with a mixed invertebrate-and-plant diet.
In the aquarium it is undemanding and takes a wide range of foods: good-quality flake and micro-pellets, frozen and live brine shrimp, bloodworm, and Daphnia, plus some vegetable matter. A varied diet with live or frozen items keeps condition up and brings out the metallic sheen. Small feedings spread through the day suit an active, near-constant grazer better than one large meal.
Mating
The Kamaka rainbowfish follows the breeding pattern typical of Melanotaenia: it is an egg-scattering plant spawner with no parental care, described as forming distinct pairs at spawning. A male sets up a display area near plants or other objects and herds a receptive female, courting with the heightened colour and fin display characteristic of the genus. As in other rainbowfishes, the display runs hardest in the morning hours after first light.
Under good conditions spawning is continuous rather than strongly seasonal, the pair laying small adhesive eggs onto fine-leaved plants over an extended period rather than in one large clutch. Males display hardest in the presence of rivals and prospective mates, so the species shows its colour best in a group — and breeders condition a shoal rather than an isolated pair to bring fish into peak spawning form.
Breeding
In captivity the Kamaka rainbowfish breeds along the standard rainbowfish lines: conditioned adults spawn over fine-leaved vegetation such as Java moss or over synthetic spawning mops, depositing small adhesive eggs that hang from the spawning medium by fine filaments. A female releases a few eggs at a time over many days rather than a single clutch, so a spawning episode is spread out and steady.
The adults offer no care and will eat their own eggs, so breeders move the mops or eggs to a separate rearing container. As with related Melanotaenia, the eggs incubate for roughly one to two weeks at typical warm breeding temperatures, with warmer water shortening the time. The tiny fry need very small first foods — infusoria, rotifers, or commercial liquid fry food — before graduating to newly hatched brine shrimp and finely crushed flake. Growth and the development of adult metallic colour are gradual, and males take time and good conditions to reach their full sheen. Specific published breeding data for this species are sparse, and these notes lean on the well-documented and consistent reproductive pattern of the genus.
In the aquarium
The Kamaka rainbowfish is a peaceful, active, shoaling midwater swimmer that makes a good community fish and is best kept in a group rather than singly or in pairs. As an energetic swimmer it appreciates open swimming space and a tank with a reasonable footprint; a minimum on the order of 20 US gal is suggested for a small group, with more room benefiting both the fish and the quality of their display.
Reported aquarium conditions run roughly 72–81 °F (72 to 80 °F) with soft to moderately hard water. There's a gap between hobby practice and the wild habitat worth flagging: aquarium guides often suggest a pH around 6.5 to 7.5, but the type-locality water was distinctly alkaline at pH 8.0, reflecting the limestone basin. The fish is adaptable, yet given those hard, alkaline origins it has no need of acidic blackwater, and stable, well-filtered water matters more than precise numbers. Keep tankmates similarly sized and peaceful — other rainbowfishes and calm community species suit it well.
Conservation
Melanotaenia kamaka is assessed as Least Concern (LC) on the IUCN Red List, in an assessment dated 5 December 2019. The category reassures, but the species is a narrow endemic: its entire known wild range is the Triton Lakes system near Triton Bay, one small cluster of lakes. A fish that confined has little buffer against localised threats — habitat change, water-quality shifts, an introduced non-native — even when the current data read as Least Concern.
The lakes sit in a remote, sparsely populated part of West Papua, which has helped limit direct human pressure so far. The Kamaka rainbowfish is also kept and bred in the hobby, and ready tank-bred stock cuts any need for ongoing wild collection. Aquarists can back the species' long-term security by keeping and propagating captive-bred lines, holding a hobby population independent of its single small wild home.