Taxonomy & naming
Rasbora wilpita was described in 1991 by Maurice Kottelat and Rohan Pethiyagoda on the basis of material collected from the Wilpita area of Sri Lanka's wet-zone lowlands. The Catalog of Fishes (Eschmeyer, CAS) records it as a valid species within Rasbora, a large and taxonomically complex genus of Asian cyprinids. Throughout the twentieth century Rasbora served as a catch-all for a great many small, shoaling cyprinids across South and Southeast Asia; since the 1990s a series of revisionary works have carved out satellite genera — Boraras, Trigonopoma, Brevibora, Kottelatia, Rasboroides and others — leaving a reduced but still substantial core Rasbora. Rasbora wilpita has not been reassigned and sits in the main genus under its original combination.
The species is characterised by several diagnostic morphological features: a pronounced symphysial knob on the lower jaw, a conspicuous maxillary lateral process, and meristics including 36 vertebrae. These are subtle structural details shared with a subset of Sri Lankan Rasbora, a fauna that Kottelat and Pethiyagoda surveyed extensively in the late 1980s and early 1990s, describing several new species from the island's forest streams. The species epithet wilpita refers directly to the locality — Wilpita, in Sri Lanka's Ratnapura District — from which the type material was taken.
Morphology
Rasbora wilpita is a moderately slender cyprinid reaching approximately 3 in standard length according to FishBase — somewhat larger than many of its congeners. Body depth runs between 24.7 and 29.3 percent of standard length, giving it a slightly more fusiform profile than the deeper-bodied rasboras. Head depth is 54 to 62 percent of head length. The lower jaw bears a distinct symphysial knob and the maxillary lateral process is conspicuous — osteological characters used by Kottelat and Pethiyagoda to distinguish it from other Sri Lankan species.
Coloration in life tends toward a silvery body with an iridescent sheen that likely inspired the common name Sri Lankan Rainbow Rasbora, though detailed colour descriptions from fresh specimens in the wild are sparse in the accessible literature. The fish is benthopelagic and swims in the lower to mid water column. Fin counts and vertebral formula (36 vertebrae) are among the characters given in the original description.
Habitat
This species is known from the south-western wet zone of Sri Lanka, specifically within the Nilwala, Gin and Kalu river drainages — all rivers that drain the island's mountainous interior southward and westward to the Indian Ocean coast. Within these systems it occupies shallow, slow-flowing or near-sluggish streams under dense closed-canopy forest, where the water is soft, lightly stained and heavily shaded by riparian and overhanging vegetation.
The habitat is characteristic of Sri Lanka's remaining lowland rainforest fringe: streams that run through or alongside intact forest, with substrates of leaf litter, fine sediment and submerged roots. The species is a softwater specialist and shows no apparent tolerance for the degraded, sun-exposed conditions that now prevail across much of its former range. iNaturalist survey notes emphasise the heavily shaded, sluggish character of occupied sites. The Wilpita locality from which the type was described has become the defining reference point for its known distribution, and some sources treat the species as effectively a single-locality endemic at the scale of occupied stream length.
Feeding
No published dietary study is available specifically for Rasbora wilpita. By analogy with other small Rasbora of shaded forest streams, and consistent with its benthopelagic habit and position in the water column, it is assumed to feed on small invertebrates — aquatic insect larvae, small crustaceans, worms and organic detritus — supplemented by whatever is available at the surface and in the water column in its low-productivity, heavily shaded habitat.
In the aquarium, hobbyist accounts suggest it accepts standard small foods: fine flake, micro-pellets and live or frozen items such as daphnia, artemia nauplii and bloodworm. Given the soft, clean and dimly lit conditions it requires, feeding should be calibrated to the relatively low-energy environment the species comes from rather than the richer, brighter conditions typical of less specialised cyprinids.
Mating
Rasbora wilpita is an egg-scattering, non-guarding spawner in the typical rasbora manner. No published account of courtship behaviour in this species is available, but the reproductive biology follows the standard pattern for the genus: a receptive male pursues a gravid female through vegetation or over substrate, and eggs and milt are released together in brief pairings without nest construction, territory defence or any lasting pair bond.
Spawning likely occurs in shallow, slow-moving water over fine-leaved vegetation, roots or leaf litter — the micro-habitats available in its forest-stream environment. As in other Rasbora, the eggs are probably weakly adhesive or non-adhesive and settle among the substrate after release. There is no parental care of any kind.
Breeding
Captive breeding of Rasbora wilpita has not been documented in the mainstream aquarium literature, and the species is rarely available in the trade. Based on general rasbora practice, hobbyists who obtain it would approach breeding as they would other softwater Sri Lankan cyprinids: a species tank with very soft, slightly acidic water, subdued lighting, fine-leaved plants or moss, and a group of well-conditioned adults. Eggs scattered over the substrate or among plants should be protected from the adults, as no parental care is provided and eggs are likely to be eaten.
Given the rarity and conservation status of this species, any captive breeding that succeeds would be of real value to reducing collection pressure on wild populations. The challenges are primarily in replicating its very specific habitat chemistry — soft, clean, shaded water at temperatures appropriate to lowland Sri Lankan streams — rather than any unusual reproductive biology.
In the aquarium
Rasbora wilpita appears only rarely in the aquarium trade, where it is sometimes offered as Sri Lankan Rainbow Rasbora or Wilpita Rasbora. It requires soft, clean water with low dissolved minerals, moderate to low temperature consistent with its lowland wet-zone origins, and subdued lighting that replicates the dense canopy cover of its natural habitat. A species tank or a quiet biotope setup with other Sri Lankan endemics would suit it best.
As a shoaling cyprinid it should be kept in groups of at least six, and preferably more, to reduce stress and encourage natural behaviour. It is a small and presumably non-aggressive fish unsuited to competition with robust or boisterous tankmates. The scarcity of the species in the trade, its Vulnerable status, and the very restricted known wild population mean that prospective keepers should verify the source of any fish offered and favour captive-bred stock if it becomes available.
Conservation
Rasbora wilpita is assessed as Vulnerable (VU) on the IUCN Red List, with the most recent assessment dated 29 July 2019. The species is a single-locality endemic in practical terms: its known distribution is confined to the Wilpita stream system and adjacent drainages (Nilwala, Gin and Kalu) in a small area of Sri Lanka's wet-zone lowlands, and estimates suggest that fewer than approximately 700 metres of its habitat currently remain undisturbed. Some assessors have considered an Endangered (EN) rating to better reflect the continuing habitat pressure, though the published IUCN status as of 2019 is VU.
The primary threat is deforestation. Sri Lanka's south-western wet zone has lost the great majority of its original lowland rainforest to agriculture, plantation monoculture (rubber, tea, coconut and oil palm), and settlement expansion. The forest-shaded, clean, soft-water conditions that Rasbora wilpita requires are directly dependent on intact riparian and catchment forest; stream exposure, increased sedimentation and water-quality changes that follow canopy removal are likely incompatible with the species' survival. Aquarium collection may add pressure but is secondary to habitat loss. Conservation of this species is inseparable from the conservation of Sri Lanka's remaining lowland wet-zone forest patches and the stream systems they shelter.