Taxonomy & naming
Chilatherina fasciata was described by the German-Dutch zoologist Max Weber in 1913, originally placed in another genus and later combined into Chilatherina, which is reflected in the parenthetical authority "(Weber, 1913)". Eschmeyer's Catalog of Fishes governs the valid name; the species sits in the family Melanotaeniidae, the true rainbowfishes, within the order Atheriniformes. Chilatherina is a small New Guinea genus closely allied to the larger genus Melanotaenia, from which it is separated chiefly on details of mouth and dentition.
The genus name Chilatherina combines the Greek cheilos, meaning "lip", with atherina, the classical Greek name for the smelt or sand-smelt — a reference both to the fish's silverside relatives and to features of the mouth. The specific epithet fasciata is Latin for "banded" or "barred", for the dark vertical bars on the lower sides of mature males. The hobby knows it simply as the barred rainbowfish, and occasionally by regional names tied to the New Guinea waters it inhabits.
Weber's description drew on material from northern New Guinea, and the species has since been recorded widely across that drainage. As with many rainbowfishes, populations from different river systems differ noticeably in colour, and the taxonomy at the population level is best treated with caution; the broad species concept used here follows the standard reference works rather than attempting to resolve local forms.
Morphology
Chilatherina fasciata is a fusiform, laterally compressed rainbowfish reaching about 4.5 in in standard length, with most aquarium specimens somewhat smaller; some hobby sources cite an overall maximum closer to 4.5 in. Like other members of the family it carries a divided dorsal fin — a short spinous anterior portion followed by a longer soft-rayed posterior portion — together with a long-based anal fin. Reported meristics give the first dorsal 5 to 8 spines, the second dorsal 11 to 16 soft rays, and the anal fin a single spine with 21 to 28 soft rays, a fin formula typical of the genus.
The base coloration is a brown to bluish-green over the upper half of the body, fading to white or yellowish below, with the scales finely edged in pale yellow to give a reticulated sheen. A distinct dark mid-lateral stripe runs along the flank. The bars that give the species its name are best developed in adult males, several diffuse blackish marks on the lower sides above the front of the anal-fin base; the fins run from dusky grey to yellowish.
Colour is strongly geographic. Because the New Guinea river systems isolate populations from one another, fish from different drainages differ in the intensity and hue of the body and fins. Breeding males go further, flushing bronze-to-vermilion over the top of the head during display — a transient nuptial colour rather than a fixed adult feature.
Habitat
The barred rainbowfish is native to the freshwaters of northern New Guinea, where it occupies lowland tributaries and streams running through hilly terrain up to roughly 1312–1640 ft elevation. Recorded localities span the mouth of the Sermowai River and tributaries of the Markham, Ramu, Sepik, Pual and Mamberamo river systems, and it is also known from Lake Wanam near Lae in Papua New Guinea. The species thus straddles both the Indonesian (West Papua) and Papua New Guinean portions of the island, at latitudes of about 1 to 7 degrees south.
Typical habitat is clear, slow-flowing rainforest stream over gravel and sand strewn with leaf litter and organic debris, and the species turns up in some lakes too. It favours sunlit stretches, which grow the filamentous green algae it grazes on. By rainforest standards the water is warm and hard-to-alkaline.
FishBase reports the species from tropical waters at 28 to 32 degrees Celsius, with pH around 7.0 to 8.0 and hardness of roughly 9 to 19 dH — warm, mineral-rich water that sets this rainbowfish apart from the soft-water lowland species. The sources agree on these numbers, and they apply equally to the wild and the tank.
Feeding
In the wild, Chilatherina fasciata is an omnivore that feeds in the upper and middle water column. It takes small aquatic and terrestrial insects, small crustaceans, and filamentous green algae grazed from sunlit surfaces — the documented preference for well-lit water follows directly from that algae in the diet.
In the aquarium it is undemanding and eats almost anything offered. Good flake and small pellets make a fine staple, backed up with frozen and live foods such as Daphnia, brine shrimp, and bloodworm, plus some vegetable or algae-based matter to echo the wild diet. A regular live or frozen component improves both colour and breeding condition.
As a near-constant grazer it does better on small amounts several times a day than on a single large feeding — which also keeps water quality steady at the warm temperatures it needs.
Mating
Chilatherina fasciata is an egg-depositing, plant-spawning rainbowfish with no parental care. Males are competitive and, in the breeding context, pushy toward females, so breeders keep two or three females per male to spread that attention rather than pairing fish off singly. A dominant male courts with heightened colour, the head flushing bronze to vermilion as he displays.
Like rainbowfishes generally, the fish display and spawn most in the hours after first light. A receptive female follows a displaying male into fine-leaved plants or a spawning medium, where eggs go down a few at a time over an extended period rather than in one clutch. Males show off hardest against rivals and in front of receptive females, so the fish look their best kept as an active group.
Fish from different river systems interbreed readily in captivity, so anyone wanting to preserve a particular wild form keeps collection localities apart.
Breeding
Breeding follows the standard rainbowfish pattern and is well within reach with conditioned adults. Bring the fish into condition on live and frozen foods, and give them a spawning medium — Java moss or a synthetic mop — for the adhesive eggs, which hang from it by fine filaments.
Spawning runs over many days, a female releasing up to roughly 30 eggs a day rather than one large batch. At the top of the temperature range the eggs hatch in about 8 to 10 days. The adults offer no care and will eat the eggs, so breeders move the mop or eggs to a separate rearing container.
The fry are tiny at hatching and need correspondingly fine first foods — infusoria or powdered flake — before moving on to newly hatched brine shrimp. Growth is slow, and the full nuptial colour of males arrives only with maturity, so patience is part of raising good stock.
In the aquarium
An active, peaceful, shoaling fish, best kept in a group of six or more — that settles the fish and brings out the males' colour as they display against one another. It is a fast, restless swimmer, so a long tank with an open central lane matters more than sheer volume; hobby sources advise at least three feet, and four feet or more for an adult group. They are good jumpers, so a secure, well-fitted lid is not optional.
Match the water to the species' warm, hard-to-alkaline origins rather than the soft-water defaults often assumed for tropical fish. It does best at 28 to 32 degrees Celsius, with pH around 7.0 to 8.0 and moderate to fairly hard water (roughly GH 5 to 15, dH 9 to 19). The warmth is a real requirement, not a preference. Stable conditions and good filtration count for more than hitting exact numbers.
Give it tankmates of similar size, active and peaceful — other rainbowfishes, larger tetras, and peaceful barbs and rasboras all work, as long as they can hold their own at feeding time. Hardy and long-lived, with a lifespan up to about eight years, it does well in a planted tank with open swimming space and bright light, which shows off the colours and prompts natural grazing and morning display.
Conservation
Chilatherina fasciata is assessed as Least Concern (LC) on the IUCN Red List, with the most recent assessment dated 5 December 2019. The listing reflects a broad distribution across several major river systems of northern New Guinea, which leaves the species far more resilient than the narrowly endemic rainbowfishes confined to single lakes.
With a range spanning the Markham, Ramu, Sepik, Mamberamo and other drainages, plus presence in lakes such as Lake Wanam, trouble in any one system is unlikely to threaten the whole. The fish is also reckoned to have low vulnerability to fishing and is harmless to humans.
The broader regional concerns are the familiar ones for New Guinea waters — habitat alteration and the introduction of non-native fishes, which can hit individual populations even where the overall status is secure. Widespread captive breeding in the hobby takes most of the collecting pressure off wild stocks. Local population trends remain poorly documented, and the strong geographic variation across the range is itself a reason to keep the wild populations distinct.