Taxonomy & naming
Rasbora spilotaenia was described by Hubbs and Brittan in 1954 and remains placed in the genus Rasbora under the Catalog of Fishes (Eschmeyer, CAS), the authority for valid names. The genus Rasbora in its broad sense has been substantially revised since the late 1990s: Kottelat and Witte (1999) and subsequent workers carved out several segregate genera — among them Boraras, Trigonopoma, Brevibora, Kottelatia, Trigonostigma and Rasboroides — from what was formerly a large, heterogeneous Rasbora. The species remaining in a restricted Rasbora are concentrated in Southeast Asia and include several Sumatran endemics; spilotaenia is one of these.
The specific epithet spilotaenia is Classical Greek in origin: spilos (σπῖλος), meaning 'spot' or 'stain', and taenia (ταινία), meaning 'band' or 'stripe'. The name thus alludes to a spotted or banded lateral marking, the defining patterning element of the species. No common name is in widespread use for this fish in the hobby literature.
Morphology
Rasbora spilotaenia is a moderately elongate, laterally compressed cyprinid. FishBase records a maximum size of 3 in standard length (SL), and field samples from North Sumatra show the most common size class falling between 6.5 and 3 in SL — placing this species at the larger end of the rasbora size spectrum. Body proportions are typical for the genus: a slightly forked tail, a small terminal mouth, and a slender but not whip-thin build suited to life in moving water.
The specific epithet references a spotted or banded lateral pattern. Detailed pigmentation data from the primary description and field material are sparse in the accessible literature, but the name indicates a horizontal marking element along the flank — a feature shared with many Rasbora in the same size class from Sundaland. Full coloration under live conditions in natural light is not well documented in widely available sources.
Habitat
The type locality of Rasbora spilotaenia is Aek Kanan, a river in North Padang Lawas Regency, North Sumatra. Field measurements at this site recorded a mean water temperature of 81 °F, a pH of 5.67 (distinctly acidic), dissolved oxygen at 6.6 mg/L, water depth around 3 ft, and a moderate current velocity of 2 ft/s — a flowing, oxygen-rich tropical stream rather than still water or a peat swamp.
The acidic pH and Sumatran provenance place spilotaenia in the spectrum of soft, dark-water stream fishes typical of the island, even if its specific habitat is a moving river rather than the stagnant blackwater peat pools that characterise some Sundaland rasboras. The species is confirmed as a Sumatra endemic; no occurrences outside Indonesia are known.
Feeding
No detailed dietary study of Rasbora spilotaenia in the wild appears in the accessible literature. By analogy with other similar-sized Rasbora from comparable Sundaland stream habitats, the diet is likely omnivorous: small invertebrates taken from the water column and surface — aquatic insect larvae, small crustaceans, and terrestrial insects that fall onto the water — supplemented with algae and organic fine matter.
Its stream habitat with moderate current suggests an active, mid-water forager capable of holding position in flow and intercepting drifting prey. In an aquarium setting, it would be expected to accept most standard small-fish foods, including quality flake and pellets alongside frozen or live foods such as daphnia and bloodworm.
Mating
Rasbora spilotaenia, as a member of the genus Rasbora, is an egg-scattering, non-guarding spawner. No detailed spawning account for this species has been published in widely accessible sources, but the reproductive strategy shared across the genus involves males pursuing gravid females through the water column or among vegetation, releasing eggs and milt together in brief embraces.
There is no nest construction, no pair bond beyond the spawning act itself, and no attendance of eggs or young. Eggs are scattered over plants, substrate, or moss; adults are indifferent to them afterward and will consume them given the opportunity. Spawning in stream-dwelling rasboras is often associated with the wet season, when rising water levels and temperatures cue reproductive activity.
Breeding
No captive breeding account for Rasbora spilotaenia is documented in the widely available hobby or scientific literature, reflecting its status as an obscure species rarely encountered in the trade. Based on its biology as a stream-dwelling rasbora, the approach used for comparable species would apply: a separate spawning tank with fine-leaved plants or mesh to protect the scattered eggs from being consumed, soft and moderately acidic water matching its wild conditions (pH around 5.5–6.5, temperature near 81 °F), and the removal of adults after spawning.
Eggs would be expected to hatch within two to three days at tropical temperatures, with fry becoming free-swimming shortly after. First foods would consist of infusoria or commercial fry foods of appropriate particle size, progressing to newly hatched brine shrimp nauplii. Data on clutch size, incubation period, and fry growth rate for this species are not documented in available sources.
In the aquarium
Rasbora spilotaenia is rarely available in the hobby and is not an established aquarium fish. Its natural habitat — an acidic, moderately fast Sumatran stream at around 81 °F — provides clear guidance for anyone who obtains the species: soft, acidic water (pH around 5.5–6.5), a temperature of 79–82 °F, and adequate oxygenation with some water movement would be appropriate. A long tank with open swimming space and good filtration-driven flow would suit a fish from riverine habitat.
As a shoaling cyprinid reaching nearly 3 in, it would need a tank of appropriate size to keep a proper group and sufficient room to move. Tankmates should be selected from comparably sized, non-aggressive species that tolerate the same soft-acidic water. The scarcity of this fish in trade means that most encounters with it are likely to involve wild-caught individuals, and acclimatisation to the water chemistry of the natural habitat should take priority.
Conservation
Rasbora spilotaenia is assessed as Least Concern (LC) on the IUCN Red List, with the assessment dated January 9, 2019. The evaluation notes it as a small endemic Sumatran cyprinid, and the LC listing implies that at the time of assessment no substantial range-wide decline was detected.
Sumatra has experienced severe land-use change over recent decades, including large-scale deforestation, conversion of lowland habitats to palm oil and pulp-wood plantations, and alteration of river systems. While a species with a single-island endemic range is inherently more vulnerable to such changes than a widespread continental taxon, the species' occurrence in flowing streams with moderate current rather than peat-swamp habitat may offer some buffer against the specific threats targeting blackwater and wetland communities. Ongoing habitat degradation in Sumatra means that even Least Concern species warrant monitoring, particularly those with restricted ranges.