Taxonomy & naming
Rasbora amplistriga was formally described by Maurice Kottelat in 2000. The Catalog of Fishes (Eschmeyer, the authority for valid names) records the valid combination as Rasbora amplistriga Kottelat, 2000, with no subsequent change of genus. It belongs to the large and heterogeneous genus Rasbora, which has undergone substantial revision over the past two decades: several lineages previously housed within it have been reassigned to segregate genera — among them Boraras, Trigonopoma, Brevibora, Kottelatia, and Rasboroides — while closely related small cyprinids in the danionin radiation sit in such genera as Trigonostigma and Microrasbora. Rasbora amplistriga itself has not been moved and remains in Rasbora under the current classification.
The species is placed in the Mekong–mainland drainage element of Southeast Asian rasboras rather than in any of the Sundaland peat-swamp lineages. It is described from the lower Mekong drainage and Thai coastal rivers. As a small, recently described species from a moderately well-studied river system, it has attracted little aquarium or ichthyological attention beyond the original description and summary records in global fish databases.
Morphology
Rasbora amplistriga is a small, slender, laterally compressed cyprinid with the typical rasbora body plan: a streamlined shape, moderately pointed snout, a subterminal to slightly upturned mouth, and a forked caudal fin. Maximum recorded standard length is 1.5 in, placing it among the smaller members of the genus.
The most distinctive feature is a broad, prominent horizontal dark stripe running along the flank — the feature encoded in the species epithet amplistriga (Latin: amplus, broad or wide; striga, stripe or streak). Details of coloration beyond the lateral stripe are not comprehensively documented in accessible literature for this species; the pattern of a bold midlateral band is characteristic of numerous Rasbora species from mainland Southeast Asia and serves as the primary character distinguishing this species in its description. Sexual dimorphism is not documented in detail, though gravid females of rasboras in this size class are typically deeper-bellied than slimmer males.
Habitat
Rasbora amplistriga is recorded from the Mekong basin south of the Khone Falls — the broad, low-gradient stretch of river and associated forest tributaries spanning southern Laos and northern Cambodia — and from the smaller coastal drainage basins of south-eastern Thailand. FishBase lists the habitat type as forest streams, consistent with the riparian lowland forests that characterise this portion of the Mekong watershed.
Forest streams in this region are typically shaded, slow to moderately flowing waters with sandy or leaf-littered substrates, submerged wood and marginal vegetation. Water chemistry tends toward the soft and mildly acidic end of the spectrum, influenced by humic inputs from decaying leaf litter, though Mekong tributaries in this reach can carry a broader mineral load than the blackwaters of Sundaland. Temperatures in lowland Indochinese streams generally fall in the range of 75–81 °F through most of the year, with some seasonal variation tied to the monsoon cycle. The species is described as benthopelagic, moving through the lower and mid water columns of its stream habitat.
Feeding
FishBase assigns Rasbora amplistriga a trophic level of 3.1 ± 0.4, indicating an intermediate consumer that feeds on small invertebrates and zooplankton alongside some plant or detrital material. This position is typical of small rasboras in forest-stream habitats, where the diet is dominated by aquatic and terrestrial invertebrates — insect larvae, small crustaceans, worms and microcrustaceans — supplemented by whatever organic matter is available in the water column or at the surface.
In the aquarium, fish of this size class and feeding guild readily accept good-quality micro-pellets, small flake foods, and live or frozen invertebrate foods such as daphnia, cyclops and newly hatched brine shrimp. Varied feeding with appropriately sized live and frozen items brings out colour and condition. The small mouth of a 1 in rasbora limits particle size, and finely milled or micro-formulated foods suit it better than standard community flake.
Mating
Like all members of genus Rasbora, R. amplistriga is an egg-scattering, non-guarding spawner. No observations of courtship behaviour in the wild have been recorded for this species specifically, but the pattern across the genus is consistent: a ripe male pursues a gravid female through vegetation or over open substrate, driving her through the water column in tight parallel swimming until eggs and milt are released together in a brief, close-contact burst.
There is no pair bond, no preparation of a spawning site, and no territory. The scattered eggs — weakly adhesive or non-adhesive — settle among plants, into fine substrate, or onto leaf litter, and the adults take no further interest in them. In many small rasboras, conspecifics will eat freshly scattered eggs if the opportunity arises, so egg survival is largely a function of the density of cover available to intercept falling eggs before the adults locate them.
Breeding
No specific captive-breeding records for Rasbora amplistriga appear in the accessible hobbyist literature, and the species is rarely if ever offered in the trade. Based on its genus, it can be expected to follow the standard Rasbora egg-scattering protocol: spawning over fine-leaved plants, java moss, or a mesh-covered substrate in a separate, well-planted breeding tank with soft, slightly acidic water. Adults should be conditioned beforehand on varied live and frozen foods.
A small rise in temperature and the addition of fresh, slightly cooler water can trigger spawning, simulating the onset of the rainy season. Eggs hatch within two to three days depending on temperature; the larvae become free-swimming shortly after and accept infusoria or commercial fry foods initially, moving to baby brine shrimp nauplii as they grow. As with all rasboras, adults provide no parental care and will consume eggs and fry if not removed promptly after spawning.
In the aquarium
Rasbora amplistriga is not established in the aquarium hobby and is essentially unknown in the trade outside of occasional wild-caught shipments from Laos, Cambodia or Thailand. For the dedicated specialist, it would suit a biotope arrangement replicating the forest-stream habitats of the lower Mekong: a moderately planted tank with dim lighting, leaf litter, fine sandy substrate and gentle filtration, with water conditioned to soft, slightly acidic parameters (pH 5.5–6.8, temperature 75–81 °F).
At 1.5 in maximum, it is a micro-fish that should be kept with other small, peaceful species from the same region — comparable rasboras, small loaches or similar fish. A shoal of at least eight to ten individuals is recommended to maintain the social confidence of a schooling species. Its modest size demands attention to the dimensions of tankmates and to the fineness of filtration intakes, which should be guarded to prevent fry loss and to avoid drawing small individuals into impeller housings.
Conservation
Rasbora amplistriga is assessed as Least Concern (LC) on the IUCN Red List, with the assessment dated 24 February 2012. FishBase notes high population resilience, with a minimum population doubling time of less than 15 months, consistent with a small, fast-maturing cyprinid. Its distribution across the lower Mekong and south-eastern Thai coastal drainages gives it a moderately broad range, and it occupies forest-stream habitat that remains extensive across parts of Laos and Cambodia.
Longer-term threats in the Mekong basin include deforestation and the conversion of riparian forest — which shades, inputs leaf litter into, and structurally maintains the forest-stream habitats this species requires — as well as hydropower development in the Mekong mainstream and its tributaries. The Khone Falls reach of the Mekong, around which the original type records were made, is the site of ongoing infrastructure pressure. The IUCN status will require revisiting as the cumulative impact of basin-wide dam development on fish assemblages in the lower Mekong becomes clearer.