Taxonomy & naming
Rasbora notura was formally described by Maurice Kottelat in 2005 from specimens collected in the Terengganu drainage, Peninsular Malaysia. The species belongs to the large and heterogeneous genus Rasbora (family Cyprinidae), a genus that has seen considerable revision over recent decades as molecular and morphological studies have carved off groups into genera such as Boraras, Trigonopoma, Brevibora, Trigonostigma and Rasboroides. The Catalog of Fishes (Eschmeyer, CAS) treats Rasbora notura Kottelat, 2005 as a valid species with no synonyms recorded. The authority stands without parentheses, as Kottelat described it directly into Rasbora.
Within the genus, R. notura belongs to a cluster of stripe-patterned Southeast Asian rasboras distinguished by their lateral-line pattern and caudal-peduncle markings. No subspecies or regional variants have been recognised. The species has been recorded under no other combination since its description.
Morphology
Rasbora notura is a slender, laterally compressed cyprinid reaching up to 3 in standard length, making it a mid-sized member of the genus. The most diagnostic feature is its colour pattern: a crisp black midlateral stripe begins beneath the dorsal fin and extends to the caudal base, where it expands into a prominent, diamond-shaped dark blotch on the caudal peduncle. This blotch distinguishes the species readily from the more uniformly striped rasboras of the region.
The back is typically olive to gold-brown, the flanks silvery with the contrasting dark stripe, and the underside pale. Fins are generally clear to lightly pigmented. The species is benthopelagic in habit but observed schooling near the water surface, suggesting active mid-water behaviour typical of the genus. Sexual dimorphism has not been described in detail in the primary literature; females of similarly sized rasboras are generally deeper-bodied when gravid.
Habitat
The species is restricted to the Terengganu drainage of central and southern Peninsular Malaysia, with records extending to the island of Pulau Redang. Within this drainage it occupies headwater streams and clean middle reaches of rivers, habitually found in clear, slow- to moderate-flowing water with surface-schooling behaviour. A record from Lorang Banir stream gives an indication of its typical setting: shaded, relatively undisturbed forest streams.
The probable northern limit of its range is the Jertih area of northern Terengganu. No records outside Peninsular Malaysia are known. The Terengganu drainage is fed by montane rainforest catchments and supports generally soft, mildly acidic water — conditions typical of the interior lowland and foothill streams of the east coast of the Malay Peninsula. The species' close association with clear, clean water underscores its sensitivity to catchment disturbance.
Feeding
FishBase assigns R. notura a trophic level of 3.2, placing it in an omnivorous to lightly carnivorous feeding niche. This is consistent with the foraging habits of congeners of similar size: small invertebrates (aquatic insects, microcrustaceans), surface-fallen terrestrial prey, and organic detritus are the likely dietary staples in its forest-stream habitat.
The species' surface-schooling behaviour reported in the original description suggests active opportunistic feeding at the water surface, intercepting drifting prey items. In the aquarium it can be expected to accept a wide range of small live, frozen and dry foods, following the pattern of most generalist rasboras.
Mating
Like all rasboras and danios, R. notura is an egg-scattering, non-guarding spawner. There is no nest construction, no pair bond, and no parental care of any kind. Courtship consists of a driving male closely pursuing a gravid female through vegetation or open water, the pair releasing eggs and milt in brief, close contact.
Spawning in wild Terengganu streams is likely triggered by seasonal cues — rising water levels and temperature shifts associated with the monsoon — that cause gravid females to ripen and males to become actively territorial within the school. No dedicated study of the reproductive cycle of this species has been published.
Breeding
In the aquarium R. notura has not been extensively documented as a bred species, and detailed captive-breeding accounts are sparse. By analogy with closely related east-coast Peninsular Malaysian rasboras, it can be expected to scatter adhesive eggs over fine-leaved plants, moss clumps or the substrate in shallow, clear, slightly acidic, soft water.
A dedicated spawning setup would replicate the clear, low-conductivity water of its forest-stream origin: rainwater or RO-blended water buffered to pH 6.0–7.0, temperatures in the mid-twenties Celsius, and dense clumps of fine-leaved aquatic plants or java moss as spawning sites. Adults must be removed after spawning, as they will consume eggs and fry. The eggs likely hatch within 24–48 hours, and fry become free-swimming within a few days. No parental care is given at any stage.
In the aquarium
Rasbora notura is an uncommon species in the hobby, rarely encountered outside specialist collections focused on Malaysian cyprinids. Those who keep it describe a surface-active schooling fish most at home in groups of eight or more, in a longer aquarium with gentle current, clear water, and a dark substrate that brings out its lateral stripe pattern.
Water quality should lean toward the soft and slightly acidic: pH 6.0–7.0, low conductivity, and temperatures of 73–81 °F match the clear forest streams of Terengganu. Overhanging or floating vegetation and subdued lighting reproduce a shaded stream environment. Tankmates should be peaceful, similarly sized fishes that will not compete aggressively with this mid-sized surface shoaler. Feeding is straightforward — it accepts good-quality flake, micro-pellet, and small live or frozen invertebrates.
Conservation
The IUCN Red List assessed Rasbora notura as Least Concern in 2019, citing the absence of evidence of major population declines across its limited range. However, its entire known distribution falls within the Terengganu drainage of Peninsular Malaysia, making it one of the more geographically restricted rasboras on the peninsula.
The principal threats to its habitat are deforestation and catchment degradation in the interior of Terengganu, where logging and agricultural conversion continue to affect the clarity and quality of forest streams. Pulau Redang, where the species also occurs, supports relatively intact forest but faces tourism and coastal development pressure. The species' requirement for clean, clear water makes it more vulnerable to pollution and siltation than generalist rasboras capable of surviving in degraded habitats. Monitoring of its status in a changing Terengganu landscape is warranted.