Taxonomy & naming
Rasbora chrysotaenia was described by Arnold in 1936, published in his 'Importrückblick 1935–1936 über ausländische Süßwasserfische' in the Taschenkalender für Aquarien-und Terrarienfreunde (vol. 29, 1937). The Catalog of Fishes (Eschmeyer, CAS) records the valid combination as Rasbora chrysotaenia Arnold, 1936; GBIF lists an authority of Ahl, 1937, a discrepancy almost certainly reflecting a confusing dual publication context — the Arnold priority is accepted here.
The genus Rasbora is a large and historically messy assemblage of small Southeast Asian cyprinids. From the 1990s onward it was substantially carved up: Kottelat & Witte (1999) separated Trigonostigma and Microrasbora; Boraras, Trigonopoma, Brevibora, Kottelatia and Rasboroides were spun off at various times; the celestial pearl 'galaxy rasbora' ended up in Danio. Rasbora chrysotaenia has remained within Rasbora in the current classification and should not be confused with any of those segregate genera. No subspecies or recognised variants are recorded.
Morphology
This is a small, laterally compressed, streamlined fish with a maximum total length of approximately 1.5 in, though most wild-caught and aquarium individuals are smaller. The body is slim and torpedo-shaped, with a slightly upturned mouth appropriate for a surface-oriented feeder. The most conspicuous feature is the midlateral horizontal stripe: a continuous band of gold or brassy yellow that runs from the snout, through the eye and along the full length of the flank to the caudal peduncle, where it typically terminates in a small dark spot at the tail base.
Background body colour is pale silvery or straw-yellow above the stripe, fading to whitish on the belly; the back is often faintly olivaceous. Fins are generally hyaline and unelaborated. Sexual dimorphism is subtle: females appear fuller in the belly region when gravid, while males are slimmer. The fish closely resembles several other small, gold-striped rasboras and careful examination of the stripe extent, spot size and body proportions is needed to separate it from related species in the trade.
Habitat
Rasbora chrysotaenia is native to Southeast Asia, recorded from Malaysia and Indonesia — a distribution centring on the Sundaland bioregion spanning the Malay Peninsula, Sumatra and adjacent islands. The exact range within that area is not well documented for this species, but congeners from the same region typically inhabit small lowland forest streams, peat-swamp edges and still to slow-moving waters in forested catchments.
Sundaland peat-swamp and blackwater habitats are characterised by extremely soft, acidic water heavily stained with dissolved tannins and humic acids from decaying vegetation. Water chemistry in such systems can be extreme — pH values below 5 are not uncommon, with very low total dissolved solids and temperatures in the low-to-mid twenties Celsius year-round. FishBase records a temperature range of 72–75 °F for this species, consistent with stable lowland tropical forest waters. These habitats are among the most biologically rich and simultaneously most threatened in the region.
Feeding
Like the great majority of small rasboras, Rasbora chrysotaenia is an omnivore and opportunistic micropredator. Its upturned mouth and midwater to surface position suggest a preference for items taken from or near the surface film — small insects, aquatic invertebrates, zooplankton, fallen micro-arthropods and algal films. Specific dietary studies for this species are lacking.
In captivity it accepts standard small-particle foods without difficulty: fine flakes, micro-pellets and small frozen or live items such as newly hatched brine shrimp, micro-worms and daphnia. Its small gape limits prey size and it does best with foods scaled appropriately to its body. Feeding several times daily in modest amounts suits both its metabolism and keeps water quality stable in the small, tightly managed setups this species often occupies.
Mating
Rasbora chrysotaenia is an egg-scattering, non-guarding spawner with no pair bond and no parental investment beyond the act of spawning itself. Conditioning of adults toward readiness follows the typical small-rasbora pattern: high-quality varied food, stable soft acidic water and the visual stimulus of conspecifics are the key triggers. Males in breeding condition may develop a more intense gold flush to the lateral stripe and pursue females with persistent, close-following drives through vegetation.
Spawning involves a brief pressing together of a receptive female and an active male as eggs and milt are released simultaneously. The adhesive or weakly adhesive eggs are scattered among fine-leaved plants, root masses or over fine substrate, and the adults take no further interest in them — indeed they will eat any eggs they encounter. There is no nest, no bubble-nest, and no form of guarding or mouthbrooding.
Breeding
Breeding in captivity follows the general pattern for small Rasbora species. A well-conditioned pair or small group is moved to a separate, dedicated spawning tank with shallow, very soft and acidic water — matching the blackwater chemistry of the species' native habitat as closely as possible — and a covering of fine-leaved plants such as Java moss or spawning mops over a fine sandy substrate. A slight water change with slightly cooler water can trigger spawning.
Eggs are scattered among the plants and fall to the substrate; the adults must be removed promptly as they will consume eggs and early fry. The eggs hatch in two to three days at tropical temperatures; the tiny larvae become free-swimming within a few more days and require infusoria or commercial fry foods of equivalent particle size before graduating to freshly hatched brine shrimp nauplii. Growth is relatively slow given the fish's miniature adult size. Successful breeding records are occasional in the hobby, attesting to the species' feasibility under the right conditions.
In the aquarium
Rasbora chrysotaenia is an uncommon but not unobtainable species in the specialist trade, appearing intermittently under its common name of goldstripe rasbora. Its small size — under 1.5 in — makes it suitable for nano and planted aquaria, where it is best kept as a shoal of at least eight to ten individuals; smaller groups produce nervous, washed-out fish that fail to display the collective shimmer of the lateral stripe. It is peaceful with other small fishes and does not compete with or threaten tankmates.
The critical keeper requirement is water chemistry: this is a soft-water, acid-tolerant species from Sundaland blackwater environments and it should be maintained in soft, acidic water (pH ideally in the low-to-mid 6 range, very low hardness) with some tannin staining from leaf litter or peat to approximate natural conditions. The temperature range is narrow — 72–75 °F — and stability matters more than any absolute value. A heavily planted, low-light biotope setup suits both its comfort and its display. It is not suited to hard, alkaline community tanks and will pale and decline in such conditions.
Conservation
Rasbora chrysotaenia is classified as Data Deficient (DD) on the IUCN Red List, assessed in January 2019. The DD listing reflects the limited information available on its precise distribution, population sizes, trends and the degree to which it is exposed to habitat loss — not an inference that populations are secure.
The species' apparent restriction to the Sundaland lowlands of the Malay Peninsula and the Indonesian archipelago places it squarely within one of the most threatened freshwater biomes on Earth. Peat-swamp forests and blackwater stream catchments in this region have suffered severe drainage for palm-oil and pulpwood plantations, settlement expansion and road development. These land-use changes alter hydrology, raise pH and eliminate the canopy shade that keeps blackwater streams cool and tannin-stained. Additional pressures include aquarium collection — though its rarity in trade suggests collection is not the primary driver — and general freshwater pollution from agricultural runoff. Until the species' range and ecology are documented more precisely, its conservation status cannot be meaningfully upgraded from Data Deficient.