Taxonomy & naming
Rasbora dorsinotata was described by Maurice Kottelat and Xiuyun Chu in 1987 in the journal Spixiana (volume 10, number 3), in a paper titled 'Two new species of Rasbora Bleeker, 1860 from southern Yunnan and northern Thailand.' The type locality is Mae Nam Huey Bon, at kilometre 45 on the road from Amphoe Tha Wang Pha to Amphoe Chiang Kham in Chiang Rai Province, northern Thailand. The Catalog of Fishes (Eschmeyer, CAS) records the valid combination as Rasbora dorsinotata Kottelat & Chu, 1987.
The genus Rasbora in its historical sense was a large and heterogeneous assemblage, and from the late 1990s onward several genera were separated from it — among them Boraras, Trigonopoma, Brevibora, Kottelatia and Rasboroides. Rasbora dorsinotata has remained in the core genus and no subsequent reassignment is recorded; no synonyms or other combinations are known. The species epithet dorsinotata is descriptive Latin, from dorsum ('back') and notata ('marked' or 'spotted'), referring to the conspicuous black markings at the tip of the dorsal fin.
Morphology
Rasbora dorsinotata is a slender, laterally compressed cyprinid reaching a maximum of approximately 1.5 in (1.5 in) standard length. The body plan is typical of the mid-water rasboras: an elongate profile, a subterminal mouth, and a forked caudal fin. The dorsal fin carries 10 soft rays and the anal fin 8 soft rays.
The species is distinguished within Rasbora by two striking melanophore-based markings. The tip of the dorsal fin is sharply black, giving the fish its specific name. Along the flank, a dark lateral stripe runs from the edge of the gill cover through the mid-body and into the rear half of the caudal peduncle, where it terminates in a rounded, well-defined dark spot rather than simply fading out. The ground colour is silvery, with the back more olive-toned. No notable ornamental colour forms are known from the aquarium trade.
Habitat
The species is known from the upper Mekong and upper Chao Phraya basins in northern Thailand and northern Laos. The type locality, Mae Nam Huey Bon, is a tributary of the Nan River — a major headwater of the Chao Phraya system — in the upland terrain of Chiang Rai Province at roughly 1969–2625 ft elevation.
SeriouslyFish characterises the habitat as small tributaries with clear, flowing water, consistent with the cool hill-stream conditions typical of northern Thai drainage headwaters. Water chemistry parameters recorded for the species range from 68–77 °F, pH 6.0–7.5, and hardness in the range of 36–215 ppm (approximately 2–12 °dH), indicating moderately soft to medium-hard, near-neutral water rather than the highly acidic blackwater of lowland Sundaland peat swamps. This reflects the geology of the limestone and metamorphic uplands of the Mekong–Salween–Chao Phraya divide.
Feeding
FishBase assigns Rasbora dorsinotata a trophic level of 3.1, placing it in the lower end of the small predator range and consistent with a diet of small invertebrates. Its modest size and mid-water swimming style suggest it takes aquatic insect larvae, small crustaceans and microinvertebrates drifting in the current, supplemented opportunistically with surface-fallen terrestrial insects and fine particulate organic matter.
No detailed dietary studies of wild specimens have been published. In the aquarium, fish of this type and size accept a broad range of small prepared and live foods — quality micro-pellets, fine flake, daphnia, cyclops and newly hatched brine shrimp are all appropriate. As with most rasboras, feeding variety supports good condition and colouration.
Mating
Rasbora dorsinotata is an egg-scattering, non-guarding spawner in the manner characteristic of the genus Rasbora and of danionin cyprinids generally. There is no nest, no pair bond, and no parental care of any kind. Spawning is likely triggered by seasonal cues — rising temperature after cooler dry-season conditions, the onset of higher rainfall — as is common among northern Thai stream cyprinids that breed in synchrony with the monsoon.
Courtship takes the form typical of rasboras: a driving male pursues a gravid female closely through aquatic vegetation or among submerged roots, and the pair release eggs and milt together in a brief, rapid embrace among the plants. Eggs are weakly adhesive and settle among fine-leaved plants, moss or gravel after release. Adults give no further attention to the spawn and will consume eggs if they encounter them.
Breeding
No detailed captive-breeding accounts appear in the accessible hobbyist literature, reflecting the species' rarity in the trade. By analogy with closely related Rasbora species from similar clear, flowing habitats, the approach is straightforward: a separate spawning vessel with fine-leaved plants or Java moss, slightly cooler water (around 68–72 °F) raised slightly to simulate monsoon conditions, and well-conditioned adults fed heavily on live and frozen foods in the weeks prior to an attempt.
Eggs are scattered and weakly adhesive, settling into the plant mass or onto the substrate. The adults should be removed promptly after spawning to prevent egg predation. Larvae hatch within two to three days at tropical temperatures and become free-swimming shortly after, when they accept infusoria, rotifers and then micro-foods. The species is gregarious and SeriouslyFish recommends keeping it in groups of six or more even outside breeding attempts.
In the aquarium
Rasbora dorsinotata is seldom encountered in the hobby and commands specialist interest rather than general availability. It is a gregarious, mid-water schooling fish that should be kept in groups of at least six individuals; smaller numbers produce nervous, poorly-coloured fish and may lead to harassment of other inhabitants. Its clear-water hill-stream origins mean it does best in clean, well-oxygenated water with gentle flow, moderate hardness (soft to medium) and a near-neutral to slightly acidic pH.
A temperature of 68–77 °F suits it well, making it slightly cooler-preferring than many Southeast Asian species — the upper end of this range approaches what some aquarists maintain for subtropical fishes. Tankmates should be chosen from similarly sized, active species that share its water parameters. The bold dorsal marking and stripe-to-spot lateral pattern make it an attractive subject for a species tank or a carefully assembled hill-stream biotope. Feeding presents no difficulty: standard small aquarium foods are accepted readily.
Conservation
Rasbora dorsinotata has not been formally assessed by the IUCN Red List and carries no status under CITES or CMS. FishBase records the species as not evaluated. Its known range spans the upper Mekong and upper Chao Phraya headwater systems in northern Thailand and northern Laos — a region that has seen significant land-use change through agricultural expansion, upland deforestation and small-scale damming of hill tributaries, all of which degrade clear-water stream habitat.
The species' apparent restriction to small, clear tributary streams in upland terrain makes it potentially vulnerable to sedimentation, flow alteration and catchment disturbance, even if it is not currently recognised as threatened. Collection for the ornamental trade appears limited and is unlikely to represent a primary pressure given the species' obscurity in the hobby. A formal assessment against IUCN criteria, informed by systematic range surveys in northern Thailand and Laos, would clarify its conservation standing.