Taxonomy & naming
Rasbora aurotaenia was described by the French naturalist Georges Tirant in 1885, from specimens collected in the river systems of what was then Cochinchine (southern Vietnam). The Catalog of Fishes (Eschmeyer, CAS) maintains the combination Rasbora aurotaenia Tirant, 1885 as valid, and the authority is confirmed by GBIF and the Malaysia Biodiversity Information System.
The species belongs to the R. argyrotaenia species group, a cluster of elongate, silvery rasboras distributed across the rivers and floodplains of mainland and insular Southeast Asia. Like most members of the group, R. aurotaenia lacks the dark subpeduncular stripe that characterises certain related species, and it is set apart within the group by the distinctly yellowish or golden colouration of its caudal fin — the character encoded in its epithet. The genus Rasbora has been progressively subdivided since the late twentieth century, with genera such as Boraras, Trigonopoma, Brevibora, Kottelatia and Rasboroides carved out of it, but R. aurotaenia has remained within the core Rasbora sensu stricto.
Morphology
Rasbora aurotaenia is an elongate, fusiform cyprinid reaching a maximum recorded standard length of 6 in according to FishBase, making it one of the larger species in the genus. The body is laterally compressed but not deep, with a relatively pointed snout and a slightly upturned mouth suited to surface and near-surface feeding.
The general coloration is silvery along the flanks, with an olive or greenish tinge dorsally and a paler belly. The caudal fin is yellow to golden, a characteristic that distinguishes it from other members of the R. argyrotaenia group and gives the fish its vernacular name. The absence of a dark subpeduncular stripe (a horizontal dark mark running to the caudal peduncle) is another distinguishing feature noted in hobbyist literature on this species group. Detailed fin-ray and lateral-line counts are available in the primary description.
Habitat
Rasbora aurotaenia is a freshwater, benthopelagic species that occupies the lower and middle reaches of large drainage systems in mainland Southeast Asia — chiefly the Chao Phraya and Mekong basins, as well as the Maeklong River. Its records span Thailand and extend into adjacent countries within those drainages, with the Malaysia Biodiversity Information System additionally listing its occurrence in Malaysian waters.
FishBase characterises this species as occurring in ponds, canals and streams, often in turbid lowland water. It is typically found near the surface or in the open water column of slow-moving or standing waters rather than in rocky, fast-flowing upland streams. These lowland habitats are warm and often subject to seasonal variation, flooding during the monsoon and dropping in the dry season.
Feeding
Rasbora aurotaenia is an omnivore. FishBase records its natural diet as consisting primarily of exogenous (terrestrially derived) insects and algae, with a trophic level of 2.6 — indicative of a low-level consumer combining animal prey with plant-based food. The upturned mouth and surface-oriented behaviour are consistent with a fish that takes insects that have fallen onto the water surface as well as floating detritus and plant material.
In the aquarium this species will accept quality flake and pellet foods as a dietary base, with live and frozen invertebrates — such as mosquito larvae, bloodworm and daphnia — improving condition and stimulating natural foraging behaviour. Given its size relative to the typical small aquarium rasbora, suitably sized food items should be offered.
Mating
Like all rasboras, Rasbora aurotaenia is an egg-scattering, non-guarding spawner. There is no pair bond, no nest construction and no parental involvement beyond the act of spawning itself. FishBase notes that spawning in wild populations occurs in rivers and ponds during the rainy season, when rising water levels, increased food availability and warming temperatures serve as environmental triggers.
In spawning behaviour, an actively pursuing male follows a gravid female through the water column and vegetation, and eggs and milt are released together during close contact. The eggs, which may be weakly adhesive, settle among plants or onto the substrate, after which adults pay them no further attention and will consume them if they remain within reach.
Breeding
Breeding Rasbora aurotaenia in captivity follows the standard approach for medium-to-large egg-scattering cyprinids. A spacious, well-planted spawning tank provides cover for the spawning act and helps protect eggs from the adults. Fine-leaved plants or mesh above the substrate give the eggs somewhere to settle away from the fish. Conditioning the adults on varied live and frozen foods before the spawning attempt helps bring females into breeding condition.
Spawning is typically triggered by a water change with slightly cooler water, mimicking the onset of the rainy season, followed by a gradual return to warmer temperatures. The adults should be removed promptly after spawning, as they will readily consume the eggs. Eggs hatch within a few days and the fry become free-swimming shortly after, at which point they accept infusoria or fine powdered fry food before progressing to newly hatched brine shrimp as they grow.
In the aquarium
Rasbora aurotaenia is an uncommon species in the aquarium hobby but a rewarding one for keepers interested in larger, active cyprinids from mainland Southeast Asia. At up to 6 in standard length it requires a significantly larger aquarium than the small schooling rasboras typically encountered in the trade — a tank of at least 47 in is appropriate for a small group. Like most rasboras it is a shoaling fish and does best in numbers, displaying more natural behaviour and less stress in groups of six or more.
Water conditions should reflect its lowland river and pond origins: warm (approximately 73–82 °F), with a broadly neutral to slightly acidic pH and moderate hardness. It is not a demanding species in terms of water chemistry, tolerating the turbid, variable conditions of its natural lowland habitats reasonably well. The species is peaceful with tankmates of comparable size and not a fin-nipper; small fish may be consumed. A diet of quality flake and pellet foods supplemented with insect-based frozen foods keeps it in good condition.
Conservation
Rasbora aurotaenia is assessed as Least Concern (LC) on the IUCN Red List (2022). The species has a broad distribution across the Chao Phraya and Mekong basins and the Maeklong River — large, ecologically diverse drainages that remain extensive — and there is no evidence of a range-wide population decline that would warrant a more threatened category.
That said, the lowland river, pond and canal habitats it favours throughout mainland Southeast Asia are subject to ongoing pressures: agricultural intensification, irrigation water extraction, pollution from runoff and domestic wastewater, and the modification or drainage of floodplain wetlands. These are regional-scale pressures across its entire range rather than threats concentrated at a single site. Monitoring of populations in the more degraded and intensively farmed portions of the Chao Phraya and Mekong lowlands would help confirm the current assessment remains appropriate.