Taxonomy & naming
Gerald R. Allen and Patricia J. Kailola described Glossolepis wanamensis in 1979. It belongs to Melanotaeniidae, the true rainbowfishes of the order Atheriniformes, a group that radiates across New Guinea and northern and eastern Australia. The genus Glossolepis is a New Guinea lineage centred on the better-known red rainbowfish, Glossolepis incisus, and G. wanamensis is one of its more localised members. Eschmeyer's Catalog of Fishes records the valid name as Glossolepis wanamensis Allen & Kailola, 1979 — the spelling and authority used here.
The genus name combines the Greek glossa, 'tongue', with lepis, 'scale'. The epithet wanamensis refers to Lake Wanam, the species' only known home, west of Lae in the Morobe Province of Papua New Guinea — a toponym that fixes the fish to its type locality. Within Glossolepis, colour and body form separate the species more reliably than meristics, which overlap broadly among rainbowfishes; reported fin-ray counts run to roughly 6–8 dorsal spines and 9–11 dorsal soft rays, with a single anal spine and 18–21 anal soft rays.
Morphology
This is a moderately elongate, laterally compressed rainbowfish reaching about 3.5 in in standard length. The body is fusiform, less deeply built than the high-backed Glossolepis incisus, which gives the Wanam rainbowfish a slimmer profile. Like the rest of the family it carries the divided dorsal — a short anterior fin followed by a longer posterior one — set over a silvery to golden body.
Males are the showier sex, developing warmer golden to reddish tones, deeper sloping fins, and a fuller body; females and juveniles stay plainer, more silvery, and rounder in the fins. Colour shifts with mood and condition, as in rainbowfishes generally — a displaying male in good water flushes far brighter than a stressed or subordinate one, and lighting and diet swing the intensity seen in a tank. The meristics sit squarely in the usual rainbowfish range, so in practice you identify the fish by its slim build, golden base colour, and its Lake Wanam origin.
Habitat
The species is endemic to Lake Wanam, a roughly circular lake on a small plateau about 15 mi west of Lae in Papua New Guinea, at an elevation of around 492 ft. That single, isolated water body is the only place the fish is known from — the central fact of both its biology and its conservation status. It is a benthopelagic freshwater fish, recorded to depths of around 33 ft within the lake.
The water is warm and on the hard, alkaline side: tropical temperatures of roughly 79–86 °F, pH around 7.8 or higher, and moderate hardness (dH of 10 or more), about what you'd expect from a still plateau lake fed by a mineral-rich catchment. Confining the entire wild population to one small lake leaves it no outlying refuge — any change to Lake Wanam hits the whole species at once, and that has proved decisive in its recent decline.
Feeding
An omnivore with a relatively low trophic level (about 2.9), the Wanam rainbowfish feeds in the middle and upper water column. In the wild it takes small aquatic and terrestrial invertebrates — insects and insect larvae, zooplankton, small crustaceans — along with algae and plant matter grazed from submerged surfaces.
In the aquarium it is undemanding and eats more or less anything offered: good-quality flake and small pellets, frozen and live foods such as brine shrimp, Daphnia, mosquito larvae, and bloodworm, and vegetable foods including spirulina. A varied diet with a real live or frozen component improves both colour and breeding condition, as with other rainbowfishes. Feed small amounts several times a day rather than one large meal.
Mating
Like other rainbowfishes, the Wanam is an egg-scattering plant spawner with no parental care. The male does the courting: he intensifies his golden-red tones and flares his fins at the females, and the display is brightest in the morning after first light — a family pattern.
Males grow larger and more strongly coloured than females, with a more extended anal fin and warmer reddish tones along the breast and fin edges; females stay smaller, more muted, and rounder-finned. Rivalry sharpens the display, so the species shows its best colour with several males together. Breeders condition whole groups rather than isolated pairs to bring fish into spawning form.
Breeding
Spawning follows the usual rainbowfish pattern, over fine-leaved vegetation. Conditioned adults lay small, adhesive eggs that attach by fine filaments to plants such as Java moss or to synthetic spawning mops, the female releasing a few at a time over an extended period rather than one large clutch. Slightly warmer water at the top of the species' range is reported to trigger it.
Incubation runs about 7–10 days. The tiny fry then hang near the surface and need very small first foods — infusoria and the like — before they can take newly hatched brine shrimp and finely crushed prepared foods. Since the adults eat eggs and fry, breeders move the mops or eggs to a separate rearing container. That this species breeds readily matters: with the wild population critically threatened, aquarium-bred stock is the main reason it persists at all.
In the aquarium
An active, peaceful schooling fish, the Wanam is best kept in a group of six to eight or more, where the males display against one another and hold their colour. It is a restless mid-water swimmer and wants room to move; a tank of roughly 25 US gal or more suits a small group, with the usual rainbowfish preference for a long open swimming lane and some structure — rocks, driftwood, vegetation — around the margins for cover.
Match the chemistry to the species' hard, alkaline lake rather than to soft-water defaults: neutral to slightly alkaline, moderately hard water (pH around 7.8 and hardness near 15 dH are reported), at warm tropical temperatures. Hobby sources give a workable range of roughly 75–81 °F, the warmer end used to push breeding. Pick tankmates that are similarly sized, peaceful, and bold enough to hold their own at feeding — other rainbowfishes and easygoing community fish work well. It is hardy and reasonably long-lived, with reported lifespans of around five to seven years.
Conservation
The IUCN Red List assesses Glossolepis wanamensis as Critically Endangered under criterion B2ab(v), in an assessment dated 6 December 2019. The listing reflects extreme natural rarity — a single small lake — set against severe documented pressure on that one habitat.
The main threats are habitat degradation at Lake Wanam and the introduction of predatory tilapia, which prey on and compete with the native rainbowfish. With its whole range confined to one water body, the species has no buffer, and it has been reported as possibly extinct or near-extinct in the wild, surviving largely in aquaria. That puts unusual weight on the captive-bred trade: a narrowly endemic fish that may persist chiefly through hobbyist and association breeding programmes. Aquarists help by sourcing and maintaining captive-bred stock and by keeping the fish in well-documented breeding groups.