Taxonomy & naming
Rasbora api was described by Lumbantobing in 2010 in a paper published in Copeia (volume 2010, issue 4, pages 644–670), which erected four new species within the Rasbora trifasciata group. The Catalog of Fishes (Eschmeyer, CAS) records the valid name as Rasbora api Lumbantobing, 2010, with the type locality given as an irrigation canal tributary in Kabupaten Tapanuli Tengah, Sumatra Utara, at approximately 1°33'59"N 98°54'52"E, an elevation of around 46 metres.
The genus Rasbora is a large and historically catch-all assemblage of small Asian cyprinids. Over recent decades numerous genera have been split from it — among them Boraras, Trigonopoma, Brevibora, Kottelatia, and Rasboroides — and GBIF's taxonomic backbone places this species within Danionidae rather than the traditionally used Cyprinidae, reflecting the ongoing reorganisation of the family. Within these reclassifications Rasbora api has remained placed in Rasbora; no transfer to another genus is currently recognised by the Catalog of Fishes.
The specific epithet api is the Indonesian word for fire, a reference to the vivid fire-orange coloration of the caudal and dorsal fins that diagnoses the species. The placement of R. api within the R. trifasciata group is supported by the presence of a black midlateral stripe running posteriorly from the first lateral-line scale to a slightly wider basicaudal spot, and by the presence of stout, conical cephalic tubercles of Type A.
Morphology
Rasbora api is a slender cyprinid, reaching a maximum standard length of approximately 2 in according to FishBase. The species belongs to the Rasbora trifasciata group and is diagnosed by a well-defined black midlateral stripe that extends from the first lateral-line scale posteriorly to a slightly expanded basicaudal spot. The defining colour feature is fire-orange pigmentation on the caudal and dorsal fins, which gave rise to the specific epithet.
Meristic data from the original description include 9 dorsal soft rays and 7 anal soft rays, with a vertebral count of 31–32. The cephalic tubercles are of Type A — stout and conical — a character used diagnostically within the trifasciata group. Coloration in life has not been described in detail beyond the orange fins and the lateral stripe; the body ground colour is presumably silvery to pale as in related species.
Sexual dimorphism has not been formally described for this species. As is typical for the Rasbora trifasciata group, females are likely deeper-bodied than males when gravid, but published data are absent.
Habitat
FishBase records Rasbora api from the Kluet, Alas, Aek Batugarigis, Aek Sibundung, Batang Lumut, and Batang Toru river systems of Sumatra, Indonesia. The species occupies a notably broad range of freshwater habitat types: gravel-bottomed mountain streams with moderate current, moderately flowing turbid rivers at lower elevations, and acidic blackwater peat swamps.
This habitat breadth is unusual for a single Rasbora species and reflects the diversity of freshwater environments across the mountainous interior and lowland coastal plain of north-western Sumatra. The peat-swamp component is of particular ecological significance: Sumatran peat-swamp blackwaters are strongly acidic (pH often well below 5), tannin-stained, and very soft, presenting conditions distinct from the clearer, somewhat harder water of highland streams. Whether R. api represents a single phenotypically plastic population or an assemblage of ecological forms has not been investigated.
The type locality — an irrigation canal tributary at ~151 ft elevation in Tapanuli Tengah — indicates the species can persist in at least mildly disturbed agricultural catchments.
Feeding
No published data on the wild diet of Rasbora api are available. Based on its size, slender body form, and membership in the genus Rasbora, it is presumed to be a micropredator and omnivore in the manner typical of the group, taking small invertebrates — aquatic insect larvae, small crustaceans, zooplankton — along with organic detritus and algal matter from the water column and surface.
In the aquarium, closely related Rasbora species accept a wide range of small prepared foods, live and frozen daphnia, bloodworm, and brine shrimp nauplii. Small particle size is important given the maximum length under 2 in. Specific feeding observations for R. api in captivity have not been published.
Mating
No courtship observations for Rasbora api have been published. The species is presumed to follow the egg-scattering reproductive strategy typical of Rasbora and the broader danionid clade: a driving male pursues a gravid female through vegetation or over the substrate, and the pair release eggs and milt together with no formation of a pair bond.
Spawning in Sumatran rasboras from both clear highland streams and peat-swamp habitats is typically prompted by seasonal rainfall and temperature shifts. Cephalic tubercles of Type A — recorded for R. api in the original description — are nuptial or contact structures seen in males of the trifasciata group, suggesting intraspecific or intersexual contact during spawning chases.
Breeding
Rasbora api has not been bred in captivity as far as can be determined from published sources, and the species is effectively unknown in the ornamental trade. By analogy with other members of the R. trifasciata group and with Rasbora generally, breeding is expected to be straightforward egg-scattering over fine-leaved plants, moss, or gravel, with no parental care whatsoever — adults will consume their own eggs if not removed.
A separate, densely planted spawning tank with slightly soft, acidic water reflecting the species' peat-swamp associations would be the logical starting point for any captive breeding attempt. Eggs and fry would require very small live foods in the early stages. Because the species spans both highland stream and blackwater peat-swamp habitats in the wild, the optimal water chemistry for captive breeding remains untested.
Facts breeding mode is set based on family biology: egg-scatterer with adhesive eggs broadcast over plants and substrate, no parental care.
In the aquarium
Rasbora api is not established in the ornamental fish trade and is essentially unavailable to hobbyists as of 2026. It was described only in 2010, its native Sumatran rivers are rarely collected for the hobby, and no tank-bred stocks appear to exist. The vivid fire-orange fins suggested by its name and the original description would make it an attractive nano aquarium fish if it ever became available, suited to a heavily planted setup with soft, acidic, tannin-stained water in keeping with its peat-swamp ecology.
Should specimens become available, keeping conditions analogous to other small Sumatran rasboras would be appropriate: temperatures in the range suited to low-elevation Sumatran waters, soft to very soft water, acidic pH, and low-intensity lighting with dark substrate and leaf litter to replicate the blackwater environment. It should be kept as a shoal of at least six individuals, as all small Rasbora are social and show better colour and behaviour in groups. Compatibility with other small, non-aggressive Sumatran species such as Boraras or small Betta would be expected.
Conservation
Rasbora api has not been assessed by the IUCN Red List; it is Not Evaluated, which is typical for recently described small Southeast Asian cyprinids where assessment resources have not yet reached the species. Its absence from IUCN assessment does not imply security — Sumatra has experienced some of the most severe deforestation and peat-swamp drainage in Southeast Asia over the past three decades, and the species' recorded range encompasses both upland river systems and lowland peat swamps that are under documented pressure.
Peat-swamp habitats in Sumatra have been subject to drainage for palm oil and pulpwood plantations, large-scale burning, and peatland conversion at landscape scale — threats that have driven numerous peat-swamp-dependent fishes toward threatened status. The Batang Toru watershed, one of R. api's recorded localities, retains significant forest cover but faces hydropower development pressure. The species' tolerance of disturbed irrigation canal habitat at the type locality may provide some resilience, but the combination of restricted endemic range, peat-swamp association, and lack of monitoring leaves its status uncertain.