Taxonomy & naming
Rasbora steineri was formally described by John T. Nichols and Clifford H. Pope in 1927 on the basis of specimens from Hainan Island, China. The Catalog of Fishes (Eschmeyer, the authority for valid names) records the valid combination as Rasbora steineri Nichols & Pope, 1927, with the authority unparenthesised, meaning the species has remained in Rasbora since its original description.
The genus Rasbora is a large and historically catch-all cyprinid assemblage covering much of South and Southeast Asia. Since Kottelat and Witte's 1999 revision, a number of genera — including Boraras, Trigonopoma, Brevibora, Kottelatia, Rasboroides and Trigonostigma — have been carved out of Rasbora on morphological and molecular grounds, and the boundaries of the genus continue to be refined. Rasbora steineri itself has not been proposed for reassignment and remains placed in Rasbora under current taxonomy.
GBIF records the common name "Chinese rasbora" for this species, reflecting its primary range in southern China. The species is sometimes encountered under this vernacular in hobbyist literature and import lists.
Morphology
Rasbora steineri is a moderately large rasbora, reaching a maximum total length of 4 in, though most aquarium specimens are smaller. The body is slender, fusiform and laterally compressed in the typical rasbora fashion, with a small, slightly upturned mouth suited to feeding in the water column and at the surface.
The most diagnostic external feature is a distinct dark lateral stripe running from behind the operculum to the caudal peduncle, flanked above by a pale or silvery zone. FishBase notes 4½ scale rows between the lateral line and the dorsal-fin origin as a key meristic character that helps separate this species from superficially similar congeners in the same region. The back is typically olivaceous to brownish-green, and the flanks are silvery with a metallic sheen under good lighting.
Habitat
Rasbora steineri is a freshwater, benthopelagic species native to the drainages of southern China, Laos and Vietnam — the Indochina subregion. Its core range includes the island of Hainan (China) and mainland Indochina river systems flowing into the South China Sea.
FishBase records water parameters of pH 6.0–6.5 and a hardness of 10–15 dH, with a temperature range of 72–75 °F, indicating a preference for soft to moderately hard, slightly acidic to neutral water in the tropical to subtropical belt. In the wild this species likely inhabits slow to moderately flowing rivers, hill streams and their vegetated margins rather than strongly acidic blackwater or heavily silted lowland floodplains.
Feeding
Like most members of Rasbora, R. steineri is an omnivore. In the wild it is presumed to feed on small invertebrates — insects, aquatic insect larvae, small crustaceans and zooplankton — together with plant material and organic detritus encountered in the water column and at the surface, a diet consistent with its laterally positioned, slightly upturned mouth.
In the aquarium it is undemanding. High-quality flake and micro-pellet foods form a sound staple, and condition is maintained with regular offerings of live or frozen foods such as brine shrimp nauplii, daphnia, grindal worms and bloodworms. Keeping it in a group encourages natural feeding behaviour and reduces shyness at mealtimes.
Mating
Rasbora steineri is an egg-scattering, non-guarding spawner. No nest is built and no parental bond forms. In courtship a ripe male pursues a gravid female through fine-leaved plants or open water, pressing alongside her briefly as eggs and milt are released simultaneously.
The eggs are adhesive and fall among vegetation, plant stems or substrate. Adults, if not separated, will eat the eggs opportunistically, so providing dense planting or a spawning medium that lets eggs drop out of the adults' reach is essential when attempting controlled breeding. Spawning readiness is promoted by well-conditioned adults, stable soft and slightly acidic water, and a modest temperature rise.
Breeding
Breeding R. steineri follows the standard pattern for egg-scattering rasboras. A separate shallow breeding vessel with clumps of fine-leaved plants or a synthetic spawning mop over a mesh or layer of marbles is a common approach, allowing the scattered adhesive eggs to settle where adults cannot easily reach them.
Water for spawning should match the species' preferred parameters — pH around 6.0–6.5, temperature 72–75 °F, and low to moderate hardness. A well-conditioned pair or small group is introduced, and spawning typically occurs in the morning hours. Adults are removed after spawning to protect the eggs. Hatching takes place within two to three days at tropical temperatures, and the free-swimming larvae are initially fed on infusoria or commercially prepared fry foods, graduating to newly hatched brine shrimp nauplii as they grow. Parental care is entirely absent.
In the aquarium
Rasbora steineri is best kept as a shoal of six or more individuals, a group size that suppresses shyness, promotes natural schooling behaviour and distributes any intraspecific chasing harmlessly across the group. A planted aquarium with some open swimming space in the mid-water zone suits it well; moderate current and subdued or dappled lighting through floating plants will encourage bolder behaviour.
Water chemistry should track the species' native Indochina stream conditions: soft to moderately hard (10–15 dH), slightly acidic to neutral (pH 6.0–6.5) and a stable temperature of 72–75 °F. Compatible tankmates include other peaceful, similarly-sized cyprinids, tetras and small loaches that share a preference for soft, slightly acidic water. Its active, shoaling nature makes it a rewarding display fish for a well-planted community setup, though it is not commonly encountered in the hobby and may require sourcing from specialist importers.
Conservation
Rasbora steineri is assessed as Least Concern (LC) on the IUCN Red List (assessment dated 8 August 2010). The species has a reasonably broad distribution across southern China, Laos and Vietnam, and no evidence of rapid range-wide decline was identified at the time of assessment.
Longer-term pressures on freshwater fish communities across Indochina include agricultural expansion, deforestation-driven sedimentation, water extraction for irrigation, and pollution from industrial and domestic sources in rapidly developing river catchments. Hainan Island, the type locality, has experienced significant habitat conversion over the past century. While R. steineri currently remains secure at the species level, ongoing monitoring of Indochina's freshwater biodiversity is important given the high rate of landscape change in the region.