Taxonomy & naming
Rasbora caudimaculata was described by Volz in 1903, and the Catalog of Fishes (Eschmeyer, the authority for valid names) retains it in genus Rasbora, where it has remained without major generic reassignment. The epithet caudimaculata is Latin for 'marked on the tail' — an unambiguous reference to the prominent blotch or pattern at the base and lobes of the caudal fin that defines the scissortail look.
The scissortail complex in Rasbora has historically included several similar species distinguished by body size, fin markings and range. R. caudimaculata is distinguished from the more common and smaller R. trilineata (three-lined rasbora) by its greater adult size, different stripe configuration and partially overlapping but distinct distribution. The internal taxonomy of Rasbora sensu lato is under continued revision — various smaller species have been moved into segregate genera such as Boraras, Trigonopoma and Brevibora over recent decades — but the large scissortail rasboras have remained within Rasbora itself under current treatments.
Morphology
The greater scissortail is a large, elongate and laterally compressed rasbora with a characteristic torpedo shape suited to active midwater life. FishBase gives a maximum recorded standard length of 6.5 in, making this one of the largest species in the genus; Seriously Fish notes consistent adults above 6 in SL. The body is silvery with a faint gold or pink iridescence, and a dark lateral stripe runs from behind the head to the caudal peduncle, where it expands into a prominent black blotch.
The defining feature is the deeply forked caudal fin, each lobe tipped with a bold black band bounded by white or yellow — the scissors pattern that gives the common name. This marking is shared by several Rasbora species but is most striking and sharply defined in R. caudimaculata. The dorsal and other fins are otherwise largely hyaline. Sexual dimorphism is subtle: ripe females become noticeably deeper-bodied and more rounded in the abdomen compared with the slimmer males.
Habitat
R. caudimaculata ranges across Peninsular Malaysia, Sumatra, Borneo (including Sarawak and East Kalimantan) and Brunei — the Greater Sunda Island arc plus the peninsula that connects it to mainland Asia. Seriously Fish documents two distinct habitat types across this range: swift, rocky streams with clear, moderately hard water at pH 6.5–7.5, and sluggish peat-swamp blackwaters at pH 4.0–6.0. The species moves through both, and aquarium literature reflects the full span of these water chemistries.
In forest streams it is an active midwater schooler, oriented against current over sandy or rocky substrates under riparian forest. In peat swamps it occupies the tannin-stained, oxygen-lean, highly acidic water of tropical lowland peat formations — among the most extreme freshwater environments in the world, where pH can drop below 4.0 and light penetration is severely limited by dissolved organics. Across both habitats, water temperature sits in the range of 68–79 °F, reflecting the equatorial lowland climate of Sundaland.
Feeding
R. caudimaculata is a predatory midwater feeder whose wild diet consists primarily of aquatic and terrestrial invertebrates, with insects forming the main component. FishBase records the natural diet as exogenous insects — fallen or drifting prey taken at or near the water surface — and Seriously Fish notes a broader invertebrate diet including aquatic larvae, small crustaceans and other arthropods.
In the aquarium this translates to a preference for meaty foods: bloodworm, daphnia and Artemia are all accepted readily, and the species does well on a varied diet of high-quality frozen invertebrates supplemented with suitable dry foods. Its size and vigour mean it is a confident feeder that will compete at the surface as well as the midwater zone; smaller tankmates may find it difficult to compete at feeding time.
Mating
Like all rasboras, R. caudimaculata is an egg-scattering, non-guarding spawner with no parental involvement beyond the act of fertilisation. Spawning is triggered by the rainy-season rise in water level and warming temperatures across the equatorial lowlands of Sundaland. Sexually conditioned males pursue gravid females through the water column and among submerged vegetation, driving them into the shallows where eggs and milt are released in a brief, pressing embrace.
There is no pair bond, no territory defence and no nest. The fertilised eggs are left entirely to chance once scattered, and adults of this and related species will readily consume their own spawn given the opportunity. Captive conditioning on live and frozen invertebrates brings fish into spawning condition reliably, and the driving behaviour and gravid female silhouette are the main cues for the aquarist managing a breeding attempt.
Breeding
Breeding R. caudimaculata in captivity requires a large, well-planted tank — the species' adult size makes the standard small spawning vessel inadequate. A spacious vessel with fine-leaved plants such as Java moss, hornwort or water sprite provides scatter sites and some cover for the scattered eggs from the adults. A water change with slightly cooler, soft and acidic water mimicking the onset of tropical rains typically triggers spawning activity.
Eggs are adhesive to weakly adhesive and settle among plants and substrate. Because adults eat eggs readily, the parents should be removed or the eggs transferred after spawning is complete. The eggs hatch in approximately 24–36 hours at tropical temperatures; the larvae are initially small and require infusoria or very fine prepared fry foods before graduating to newly hatched brine shrimp as they grow. Growth rate is relatively rapid for a fish of this size, and juveniles develop the characteristic scissortail fin marking as the caudal fin matures.
In the aquarium
The greater scissortail is a rewarding but demanding aquarium fish, primarily because of its size. Adults at 6–6.5 in need a genuinely large tank — a minimum 47–59 in footprint is a reasonable starting point — with substantial open swimming space through the midwater zone. It is an active, fast-moving shoaler that does best in groups of at least five or six; singletons and pairs become stressed and can harass smaller tankmates. Compatible companions should be of comparable size and vigour.
Water chemistry should reflect the species' two-world range: soft to moderately hard (2–10°H), at pH 5.0–7.5 depending on the source population kept, and temperature between 20 and 79 °F. The aqua-fish.net source emphasises clean, well-oxygenated water with moderate flow and weekly water changes. Peat-swamp-sourced individuals may need the lower end of the pH range and benefit from tannins (peat filtration or Indian almond leaves), while stream-form fish are more forgiving. Feeding is straightforward: a varied diet of meaty frozen foods and quality pellets keeps the fish in excellent condition. Long-lived and striking, it remains a centrepiece fish for the specialist large-tank keeper.
Conservation
Rasbora caudimaculata has no confirmed IUCN Red List individual assessment publicly available; sources note its status is inferred as Least Concern based on its broad distribution across Peninsular Malaysia, Sumatra, Borneo and Brunei, and its occurrence across two habitat types with different pressure profiles. FishBase and Seriously Fish both treat it as a widespread and currently non-threatened species.
Its peat-swamp habitat is, however, under serious and accelerating pressure across Sundaland. Tropical peat swamps in Sumatra, Borneo and Peninsular Malaysia have suffered catastrophic drainage and burning for agriculture — primarily oil palm — over the past three decades, and the freshwater biodiversity of these systems is poorly understood and rarely surveyed before conversion. The stream populations face comparatively less acute pressure, but continued deforestation of riparian corridors and catchment modification for logging and plantation development represents a background threat across the range. The aquarium trade draws on wild-caught fish, but the scale of collection relative to wild populations has not been formally evaluated.