Taxonomy & naming
Chilatherina bleheri was described by the Australian ichthyologist Gerald R. Allen in 1985. Eschmeyer's Catalog of Fishes records it as the valid name, Chilatherina bleheri Allen, 1985; because the species was described in Chilatherina, where it remains, no parenthetical authority is used. It is one of around a dozen species in the genus Chilatherina, a New Guinea rainbowfish radiation closely allied to the larger and better-known genus Melanotaenia within the family Melanotaeniidae (order Atheriniformes).
The genus name combines the Greek cheilos, 'lip', with atherina, the classical Greek name for a silverside or smelt — a nod to the rainbowfishes' superficial resemblance to those slender silvery fishes. The specific epithet is a patronym honouring Heiko Bleher, the German explorer and ornamental-fish wholesaler whose collecting in New Guinea brought many rainbowfishes, this one among them, to scientific and hobby attention. Chilatherina species are distinguished from Melanotaenia largely on fin-ray and jaw characters; within the genus, C. bleheri is recognised by its colour pattern and its restricted type locality rather than by strongly diagnostic meristics, which overlap broadly among congeners (dorsal spines 5–7, dorsal soft rays 11–16, anal soft rays 21–26).
Morphology
Bleher's rainbowfish is a fusiform, laterally compressed rainbowfish reaching about 4.5 in in standard length; females and most aquarium specimens run somewhat smaller. It carries the family's divided dorsal fin — a short anterior dorsal followed by a longer posterior dorsal — and a moderately deep body that deepens further with age in dominant males.
Colour is what sells it. Mature males develop a bluish to greenish anterior body that gives way to warm reddish to orange tones over the posterior body and into the soft dorsal, anal, and caudal fins, the red intensifying when a fish is displaying. As in rainbowfishes generally, the colour is strongly mood- and condition-dependent: a courting or dominant male flushes far brighter than a stressed or subordinate one, and diet and lighting shift the intensity in captivity. Females and juveniles are plainer — silvery to yellowish, with subdued markings — the pronounced sexual dimorphism typical of the family.
Habitat
Chilatherina bleheri is a narrow-range endemic known only from Danau Bira, also called Lake Holmes, a small lake in the lower Mamberamo River system of West Papua (formerly Irian Jaya), Indonesia. The locality sits at low latitude, roughly 2–3 degrees south of the equator, in the vast lowland river network that drains the northern slope of New Guinea's central ranges. The species is a freshwater, pelagic fish of the open and vegetated water of this lake.
Reported conditions are warm and neutral-to-alkaline: water temperatures around 73–81 °F, pH at or above 7.0, and moderate hardness on the order of 8–15 dH. What defines this fish, though, is not its water chemistry but the smallness of its range. A single lake basin offers no outlying population to buffer it against local disturbance, and that pinpoint distribution is what underlies its threatened status. On its depth preferences and seasonal movements within the lake, published data are sparse.
Feeding
Like rainbowfishes generally, Bleher's rainbowfish is an opportunistic omnivore feeding in the upper and middle water column; FishBase places it at a trophic level of about 2.8. The natural diet is taken to comprise small aquatic and terrestrial invertebrates — insect larvae, small crustaceans, and insects from the surface film — together with algae and plant material, although detailed wild-diet studies for this narrowly distributed species are limited.
In the aquarium it is undemanding and accepts a wide range of foods: good-quality flake and small micro-pellets as a staple, supplemented with frozen and live foods such as Daphnia, baby brine shrimp, Cyclops, and bloodworm, plus some vegetable matter such as spirulina-based preparations. A varied diet with a real live or frozen component improves both colour and breeding condition, and because the fish feeds constantly it does best on small amounts offered several times a day rather than one large feeding.
Mating
Bleher's rainbowfish is an egg-scattering, plant-spawning species with no parental care, and under good conditions it is a frequent — often daily — spawner rather than a strictly seasonal one. Sexual dimorphism guides pairing: males are deeper-bodied and more intensely coloured, often with an extended first dorsal fin, while females are smaller, slimmer, and paler. Males display most strongly in the presence of rivals, so the species is at its most colourful, and most ready to spawn, when several are kept together.
Courtship follows the familiar rainbowfish pattern, concentrated in the early hours after first light. A displaying male intensifies his red and blue, flares his fins, and leads a receptive female into fine-leaved vegetation or spawning mops, where the pair release small numbers of eggs at a time. Breeders typically condition a group rather than an isolated pair, both to bring the fish into peak form and to elicit the competitive male display that drives spawning.
Breeding
Chilatherina bleheri breeds in captivity along typical rainbowfish lines and is regarded as a productive, if patient, project. Conditioned adults spawn over fine-leaved plants or synthetic spawning mops, depositing small adhesive eggs that hang by fine filaments from the spawning medium. Rather than a single large clutch, a female releases a few eggs at a time over many successive days.
The adults will eat their own eggs and offer no care, so breeders move the mop to a separate rearing container or replace it regularly. At breeding temperatures around 75–79 °F the eggs hatch in roughly 7–10 days. The fry are very small and hang near the surface at first, requiring tiny first foods — infusoria and rotifers — before graduating to newly hatched brine shrimp and finely crushed flake. Growth is slow and the full adult colours develop only gradually, with males taking time to reach their best red-and-blue intensity. With steady feeding and clean water, the species can be maintained and increased entirely in captivity, and a lifespan on the order of several years is reported.
In the aquarium
Bleher's rainbowfish is an active, peaceful, sociable midwater shoaler best kept in a group of six or more so that males display against one another and stay colourful. It is a strong, restless swimmer that needs a long, open swimming lane; a tank of around 47 in in length and roughly 65 US gal suits an adult group given the fish's size, activity, and the desirability of keeping a proper school.
Water chemistry should reflect the species' neutral-to-alkaline origins rather than the soft-water defaults many aquarists assume for tropical fish: it does well around pH 7–8, hardness of roughly 8–16 dGH, and temperatures of about 75–81 °F. Stable conditions and good filtration matter more than chasing precise numbers. Suitable tankmates are similarly sized and peaceful — other rainbowfishes, larger rasboras and tetras, peaceful Corydoras, and non-aggressive dwarf cichlids — while fin-nippers are best avoided. The species is hardy and long-lived for its size, but males need time and good conditions to develop their full colour, so patience is part of keeping them well.
Conservation
Chilatherina bleheri is assessed as Endangered (EN) on the IUCN Red List under criterion B1ab(v), reflecting its extremely restricted extent of occurrence — essentially a single lake, Danau Bira (Lake Holmes), in the lower Mamberamo system. A species confined to one small basin has little resilience: there is no large outlying population to absorb local declines in habitat quality or to recolonise after a disturbance, and ongoing loss of mature individuals underpins the listing.
The species is harmless to humans and is used in the commercial aquarium trade, which adds collecting pressure to an already narrow wild population. As with other threatened rainbowfishes, the useful thing aquarists can do is keep and propagate captive-bred stock rather than rely on wild-caught fish; the species spawns readily enough that this is feasible, and it stays widely held in captivity as a hedge against its precarious wild status. It has not been evaluated under CITES or the CMS.