Taxonomy & naming
Glossolepis multisquamata was described by the Dutch ichthyologists Max Weber and Lieven Ferdinand de Beaufort in 1922, in their monumental survey of the fishes of the Indo-Australian Archipelago. It was originally placed in a different combination, and the valid name is therefore written with the original authority in parentheses — (Weber & de Beaufort, 1922) — following the conventions codified in Eschmeyer's Catalog of Fishes, which governs the valid name used here. The species sits in the family Melanotaeniidae, the true rainbowfishes of New Guinea and Australia, within the order Atheriniformes.
The genus name Glossolepis combines the Greek glossa, meaning tongue, with lepis, meaning scale — a reference to scale characters used in the original generic diagnosis. The specific epithet multisquamata translates roughly as 'many-scaled', and the species is sometimes rendered with the masculine spelling multisquamatus in older literature. Its accepted English common name, Sepik rainbowfish, points to one of the major river systems it inhabits, though the species is by no means restricted to the Sepik itself.
Glossolepis is a smaller genus than its sister Melanotaenia and includes several well-known aquarium species such as the red rainbowfish, G. incisus. Within that group, G. multisquamata is distinguished as much by its ecology and its unusual water-chemistry preferences as by hard meristic characters, which overlap broadly across the rainbowfishes.
Morphology
The Sepik rainbowfish is a fairly large, robust rainbowfish. FishBase records a maximum standard length of about 4.5 in in males and around 4 in in females, after Allen's 1991 field guide to the freshwater fishes of New Guinea; hobby sources report somewhat larger overall lengths of up to roughly 5.5 in including the tail. The body is fusiform and laterally compressed, and older males in particular become notably deep-bodied with age, taking on the high-backed profile characteristic of mature rainbowfishes.
Like all members of the family it carries a divided dorsal fin — a short anterior portion followed by a longer posterior one — with the dorsal supported by roughly 5 to 7 spines and 9 to 10 soft rays, and the anal fin by a single spine and a long series of 19 to 22 soft rays. The ground colour is variable: reddish, greenish, olive, or brown, overlaid with narrow stripes that run between each row of scales in shades of yellow, orange, or red. The fins may be blackish, greenish, or reddish.
Colour in this species is strongly tied to locality and to water conditions, so populations from different river systems can look quite distinct, and an individual's appearance shifts with mood, light, and water quality. As in rainbowfishes generally, males are the larger and more intensely coloured sex, deepening in body and brightening in display, while females remain plainer.
Habitat
Glossolepis multisquamata is endemic to northern New Guinea, where it ranges across the floodplains of both Papua New Guinea and the Indonesian province of West Papua. It is associated chiefly with three major river systems — the Mamberamo in the west and the Ramu and Sepik in the east — and is recorded from roughly 2 to 3 degrees south of the equator. FishBase characterises it as the only known floodplain-dwelling rainbowfish — an unusual niche within the family.
Rather than clear upland streams, this species occupies swampy lagoons, ox-bow lakes, isolated river arms, lakes, and the small side-channels of large lowland rivers. These are typically turbid, sunlit, sluggish waters thick with aquatic plants, reeds, and submerged timber — the seasonally inundated margins of big tropical rivers. The fish is benthopelagic, working the mid-water and surface layers of these standing and slow-flowing habitats.
Water conditions reported for the species are warm and, unusually for a rainbowfish, acidic: temperatures of about 26 to 30 degrees Celsius, with a pH around 6.2 to 6.8. This soft, acidic preference sets G. multisquamata apart from the many hard-water, alkaline-loving rainbowfishes of the New Guinea highlands and Australian rivers, and reflects the tannin-stained, lowland floodplain waters it calls home.
Feeding
In the wild the Sepik rainbowfish is essentially carnivorous, feeding mainly on small invertebrates taken from mid-water or at the surface. FishBase places it at a low trophic level of about 2.7, consistent with a diet of insect larvae, small crustaceans, and other tiny prey items captured among the dense vegetation of its floodplain habitats. Hobby observations add a minor component of algae and vegetable matter, so the species is best described as a predominantly insectivorous omnivore.
In the aquarium it is undemanding at the table. It readily accepts good-quality dry foods — flake and small pellets — but does conspicuously better, in both colour and breeding condition, when these are supplemented with live and frozen foods such as brine shrimp, Daphnia, and bloodworm. As an active, constantly foraging fish, it is best fed small portions several times a day rather than a single large meal, which suits its habit of picking prey from the water column throughout the day.
Mating
Glossolepis multisquamata is a plant-spawning, egg-scattering rainbowfish with no parental care, and like its relatives it spawns over an extended period rather than in a single seasonal event. Under good conditions it matures within its first year, and sexually active fish can spawn over many consecutive days.
As in other rainbowfishes, males are the showier, more competitive sex, and courtship is most intense in the early morning. A displaying male flares his fins and intensifies his colours to court receptive females among the aquatic vegetation. Because males display most strongly against rivals, the species shows best — and breeds most reliably — when kept in groups, and aquarists typically recommend a ratio of two to three females per male to spread the males' attention and reduce harassment of any single female.
The data on wild mating behaviour specifically for this species are sparse, and most detailed accounts derive from aquarium observation, where the general rainbowfish pattern of morning, plant-associated spawning holds true.
Breeding
The Sepik rainbowfish is regarded as an easy spawner in a well-planted aquarium. Conditioned fish spawn over fine-leaved plants or a spawning medium such as Java moss, to which the small adhesive eggs attach. Spawning takes place in the early morning, with a female releasing only a few eggs each day over an extended spawning period rather than depositing one large clutch.
Because the adults will eat both eggs and fry, breeders move the moss or the eggs to a separate rearing container. The eggs hatch within roughly seven days, though incubation can stretch to around ten days in cooler water. The tiny fry are first fed infusoria, graduating to newly hatched brine shrimp as they grow, with finely crushed dry foods added thereafter.
None of this departs greatly from the standard rainbowfish routine. The early maturity and steady willingness to spawn make it a manageable subject for anyone who can provide warm, planted conditions and small live first foods for the fry.
In the aquarium
Glossolepis multisquamata is an active, peaceful schooling fish that does best in a group, ideally with several females per male so that the males display and stay colourful without overwhelming any one female. It needs a well-planted tank that still leaves open central space for swimming, with subdued, sunlit-style lighting that brings out the fish's locality-dependent colours and encourages morning display behaviour. Given the adult size and restless swimming style, a long aquarium is preferable.
Water chemistry is where this one trips people up. Unusually for the genus, it prefers warm, soft, acidic water rather than the hard, alkaline conditions many rainbowfishes favour: temperatures of about 26 to 30 degrees Celsius and a pH in the region of 6.2 to 6.8 match its floodplain origins. Aquarists used to keeping rainbowfishes in hard, basic water should take note — getting the acidity right improves both colour and breeding readiness.
It is hardy and adaptable, and gets on with similarly sized, peaceful tankmates such as other rainbowfishes and robust, non-nippy companions. Colour deepens with good feeding and the company of rivals, so a group in a mature, planted tank shows the fish at its best.
Conservation
Glossolepis multisquamata is assessed as Least Concern (LC) on the IUCN Red List (species ID 169502), reflecting its wide distribution across the floodplains of northern New Guinea and the absence of any documented range-wide threat. Unlike several narrowly endemic lake rainbowfishes of the Vogelkop region, this species occupies an extensive lowland river network spanning the Mamberamo, Ramu, and Sepik systems, which buffers it against the kind of single-basin pressures that imperil more localised relatives.
The species is not listed under CITES or CMS. As with many New Guinea freshwater fishes, the chief long-term concerns are the habitat changes that accompany development of large tropical river basins — alteration of floodplain hydrology and the spread of introduced fishes — rather than any current, quantified decline. For now, the broad floodplain range and tolerance of turbid, vegetated standing waters keep it comparatively secure.