Taxonomy & naming
The Dutch zoologist Max Weber described Chilatherina crassispinosa in 1913, in his account of freshwater fishes collected during expeditions to southern and northern Dutch New Guinea, published in Nova Guinea. Weber placed it in the genus Rhombatractus, making the original combination Rhombatractus crassispinosus Weber, 1913. The later move to Chilatherina is why the authority sits in parentheses, following Eschmeyer's Catalog of Fishes, the authority for the valid name.
Chilatherina sits within the Melanotaeniidae, the true rainbowfishes and their relatives, which radiate across New Guinea and northern Australia within the order Atheriniformes. The genus name pairs the Greek cheilos, lip, with atherina, the classical name for the silverside or smelt — a nod to the slender, silvery, atherinid-like build of these fishes. The epithet crassispinosa is Latin for the thickened spines that mark the species: crassus, thick, and spinosus, spiny.
The IUCN assessment recommends further taxonomic work, reflecting the broad, variable range the fish occupies across northern New Guinea. Meristic characters overlap among related species, as they do across much of the family, so field identification often rests as much on locality and habitat as on hard counts.
Morphology
This is a moderately elongate, laterally compressed rainbowfish. FishBase records a maximum length of about 4.5 in SL for males and unsexed specimens and roughly 3.5 in SL for females; the IUCN account cites around 4 in SL from field observations. Either way, a medium-sized rainbowfish, not one of the family's giants.
It carries the divided dorsal fin of the Melanotaeniidae — a short anterior dorsal followed by a longer posterior one. Reported meristics run to 5 to 7 dorsal spines and 8 to 12 dorsal soft rays, a single anal spine, and 19 to 24 anal soft rays. The common name, silver rainbowfish, says most of what there is to say about colour: a silvery, understated fish in a family famous for the opposite. Mature males should be deeper-bodied and more strongly coloured than females, as in rainbowfishes generally, with display intensity shifting by mood and condition — but colour detail beyond the silvery ground is thin in the sources, and is not asserted here past what the data support.
Habitat
This is a freshwater, pelagic fish of tropical northern New Guinea, recorded across a latitude band of roughly 2 to 7 degrees south. FishBase and the IUCN put it in hilly or mountainous terrain at elevations of about 328–1969 ft, in permanent rivers, streams, and creeks rather than still lake water.
The IUCN account is specific about the habitat: clear-water streams, usually running through rainforest, over rocky, gravel, or sandy bottoms, where the fish gather in exposed sections that catch full sunlight for most of the day. The water is warm and hard-to-alkaline — about 25 to 30 degrees Celsius, pH roughly 7.7 to 8.5 — what you would expect of clear, mineral-bearing montane streams.
The range is wide. The fish occurs in the Markham, Gogol, Ramu, Sepik, and Pual river systems of Papua New Guinea and in the Mamberamo River of Indonesia's Papua Province, plus numerous independent coastal drainages between Lae in Papua New Guinea and the mouth of the Mamberamo. That spread across several major basins is what underpins its secure conservation status.
Feeding
An omnivore that feeds in the water column on small items. FishBase's trophic modelling places it at about 2.9, consistent with a diet built on micro-invertebrates and other small prey rather than on fishes.
In the clear, sunlit rainforest streams it lives in, that diet would take in aquatic insect larvae and other small invertebrates, terrestrial insects dropping onto the surface, and grazed algae and plant material — the opportunistic feeding of rainbowfishes generally. No gut-content study specific to this species turns up in the sources, so the picture here is a general one drawn from the trophic level and family habits.
The cited sources hold no aquarium feeding record either. Like rainbowfishes generally, it would be expected to take a varied diet of prepared, frozen, and live foods — but the fish is not in the trade, so practical husbandry notes are sparse.
Mating
No one has documented courtship or mating in Chilatherina crassispinosa in the available sources, so what follows rests on the reproductive pattern of the Melanotaeniidae rather than on study of the fish itself.
Rainbowfishes are egg-scattering, plant-spawning fishes. Males court females with colour displays, usually most intense in the morning, over fine-leaved vegetation; the eggs attach by fine adhesive filaments to the substrate, and the adults give no care afterward. Whether C. crassispinosa departs from that is simply not recorded, and no claim is made beyond the family norm.
Its preference for exposed, sunlit stream reaches hints that light and warmth help trigger and time spawning, as in many rainbowfishes — but for this fish that is inference, not observation.
Breeding
There are no captive breeding records for Chilatherina crassispinosa in the available sources, which follows from its absence from the trade. So the breeding picture comes from genus- and family-level husbandry, not from documented spawnings of this fish.
Chilatherina rainbowfishes, like the Melanotaeniidae generally, are egg-scattering spawners. They deposit small adhesive eggs onto fine-leaved plants or synthetic mops, releasing them in small numbers over an extended period rather than in a single clutch. The eggs hang by fine filaments and get no parental care; the adults will eat their own eggs and fry given the chance. Incubation across the family runs about one to two weeks at warm temperatures, after which very small fry need correspondingly small first foods.
FishBase rates resilience as medium, with an estimated minimum population doubling time of 1.4 to 4.4 years — a measure of reproductive turnover, not an aquarium protocol. Clutch sizes, hatching times, and rearing details for this species are not available, and are not invented here.
In the aquarium
The IUCN flags this fish as having aquarium potential, but it is not in the trade. There is consequently little hobbyist husbandry literature specific to it, and the notes below are extrapolated from its wild habitat and from the keeping of related rainbowfishes — not from a body of experience with this fish.
The wild parameters point hard toward alkaline conditions: about 25 to 30 degrees Celsius, pH roughly 7.7 to 8.5, in clear, well-oxygenated, flowing water over gravel, rock, or sand. It comes from bright, exposed stream reaches, so strong lighting and good water movement would suit it. A medium-sized, active, schooling rainbowfish at around 4–4.5 in wants a long tank with open swimming space, and should be kept in a group.
With the species essentially absent from cultivation, treat any husbandry guidance as provisional and built on family norms. The safest starting point is to copy the warm, hard, alkaline, fast-flowing rainforest-stream conditions described from the wild.
Conservation
The IUCN Red List assesses Chilatherina crassispinosa as Least Concern (ver. 3.1). The assessment was made on 6 December 2019 and published in 2020 (Allen, Hammer & Unmack, 2020; e.T161079519A161079697). The population trend is stable, and the species is described as common.
The listing rests on a wide distribution across northern New Guinea — the Markham, Gogol, Ramu, Sepik, and Pual rivers in Papua New Guinea, the Mamberamo in Indonesia, and numerous independent coastal drainages — with no major range-wide threats. The fish occurs inside natural reserves across that range. What threats exist are local: introduced invasive fishes are thought to have driven declines in the main channels of the Sepik and Ramu over the late 1990s and 2000s, but never on a range-wide scale.
The IUCN account lists no species-specific conservation actions beyond the incidental protection of those reserves, and recommends further taxonomic research. Since the fish is not exploited by the aquarium trade, collecting pressure is not among its threats.