Taxonomy & naming
Rasbora armitagei was formally described by Silva, Maduwage and Pethiyagoda in 2010 in Ichthyological Exploration of Freshwaters (volume 21, number 1), as part of an ongoing program to document the remarkable freshwater fish fauna of Sri Lanka's Southwest Wet Zone. The holotype is catalogued as WHT 7661; paratypes WHT 7662–7843 are deposited in the Wildlife Heritage Trust collections. The Catalog of Fishes (Eschmeyer, the authority for valid names) records the valid combination as Rasbora armitagei Silva, Maduwage & Pethiyagoda, 2010.
The genus Rasbora, as presently defined, remains one of the larger cyprinid genera in South and Southeast Asia, though decades of systematic revision have carved numerous former 'Rasbora' species into segregate genera — among them Boraras, Trigonopoma, Brevibora, Kottelatia, Rasboroides, and Trigonostigma. Rasbora armitagei has not been proposed for transfer; it remains within the core Rasbora assemblage. Within Sri Lanka, the description of this species was part of a survey revealing substantial undocumented diversification of rasboras in the island's wet-zone river systems.
Morphology
Rasbora armitagei reaches a maximum recorded standard length of 2.5 in, making it a moderately sized rasbora by genus standards. The type locality material was collected from clear, shaded streams in inland rainforest, consistent with a species adapted to well-oxygenated, relatively stable conditions rather than open, sun-exposed waters.
Detailed morphometric data from the original description place this species within the characteristic Rasbora body plan: a laterally compressed, fusiform body suited to open-water schooling in moving water, with the proportions that distinguish it from the smaller Sri Lankan congeners described in the same survey. Coloration in preserved specimens and live fish from the type locality reflects the shaded stream environment — precise details of lateral stripe pattern and fin coloration are recorded in the original description.
Habitat
The type locality is a tributary of the Kalu Ganga (Kalu River) near Weralugahamulla, close to Rakwana in Sri Lanka's Sabaragamuwa Province, at approximately 6°30'N, 80°36'E. Rasbora armitagei is associated with clear, slow-flowing to moderately flowing streams with gravel and boulder substrata, shaded by the canopy of inland rainforest within Sri Lanka's Southwest Wet Zone — a globally significant biodiversity hotspot under severe and continuing deforestation pressure.
The Southwest Wet Zone receives high annual rainfall and maintains perennial stream flow, and its forest-shaded streams retain relatively stable temperatures, high dissolved oxygen and low to moderate turbidity. Available data do not include formal water chemistry measurements (pH, hardness, temperature ranges) for the capture sites of this species; the environment is consistent with the soft, mildly acidic to neutral waters typical of Sri Lankan rainforest streams, though generalisation must be treated cautiously in the absence of measured values.
Feeding
No dedicated feeding study has been published for Rasbora armitagei. By analogy with other Rasbora species of similar size occupying comparable shaded forest-stream habitats, the diet likely consists of small aquatic and terrestrial invertebrates — insects (both aquatic larvae and adults falling to the water surface), small crustaceans and worms — supplemented by algae and fine organic detritus drifting through the stream.
In the aquarium, wild-caught or captive-raised individuals of closely related Sri Lankan rasboras accept small live and frozen foods (daphnia, bloodworm, brine shrimp) alongside quality micro-pellets and fine flake, with live and frozen items maintaining condition and promoting natural foraging behaviour. Given the species' conservation status, captive-bred stock from responsible breeders is strongly preferred over wild collection.
Mating
Rasbora armitagei has not been studied in detail in the context of reproductive behaviour. As a member of the genus Rasbora and consistent with all known members of the broader danionin clade, it is an egg-scattering, non-guarding spawner. In related forest-stream rasboras, spawning is typically triggered by water level and temperature cues associated with rainfall seasonality. A ready male pursues a gravid female through vegetation or over the gravel substrate, and eggs and milt are released in brief, close contact between the pair.
There is no pair bond and no parental care of any kind. Eggs are scattered over fine-leaved plants, submerged roots, moss or gravel, and adults may consume them given access. No nest is built and no substrate is prepared before spawning.
Breeding
No published account of successful captive breeding of Rasbora armitagei is available in the accessible literature, reflecting both the species' rarity in the trade and its Critically Endangered status. In principle, the approach used for closely related Sri Lankan and South Asian rasboras would apply: a separate, shaded spawning tank with fine-leaved plants or a thin moss layer, soft slightly acidic water, and a well-conditioned group.
Eggs are scattered adhesively over plants or fine substrate and hatch within two to three days at tropical temperatures. Adults should be removed promptly after spawning to prevent egg predation. Fry become free-swimming a few days post-hatch and accept infusoria followed by newly hatched brine shrimp nauplii as initial foods. Given the species' fragile wild status, any captive breeding effort represents genuine conservation value.
In the aquarium
Rasbora armitagei is rarely if ever available in the aquarium trade, and its Critically Endangered status means that wild collection is both ecologically harmful and, in Sri Lanka, subject to national wildlife protection law. Any specimens encountered in the hobby are likely to be captive-bred from privately maintained or ex-situ conservation breeding stock, and provenance should be confirmed before purchase.
For a keeper with access to responsibly sourced stock, the appropriate setup mirrors the species' native habitat: a shaded, longer aquarium with gentle filtration, a dark substrate, driftwood and fine-leaved plants to replicate the shaded rainforest stream. The soft, mildly acidic to neutral water chemistry typical of Sri Lankan lowland streams suits this species well. It should be kept as a small shoal of at least six individuals. Its modest size (to about 2.5 in) and presumed peaceful disposition make it compatible with other small, undemanding fish from comparable water-chemistry requirements.
Conservation
Rasbora armitagei is assessed as Critically Endangered (CR) on the IUCN Red List, evaluated against criteria B1ab(iii)+2ab(iii) in an assessment published 7 August 2019. These criteria reflect an extremely small extent of occurrence and area of occupancy, combined with continuing decline in the quality and extent of its specialized rainforest-stream habitat. The species is known from only a small stream in the Kalu River basin, and its entire range falls within Sri Lanka's Southwest Wet Zone — a region that has lost the vast majority of its original lowland rainforest to plantation agriculture, smallholder farming, settlement and infrastructure development over the past century.
The principal threats are habitat conversion and degradation: deforestation and associated siltation alter stream flow, water quality and canopy shading, eliminating the conditions this species depends on. Its exceedingly limited range means that even local events — a single land-use change, a pollution incident or a severe drought — could eliminate the known population. No specific conservation measures targeting this species are documented in the available literature; protection of remaining rainforest fragments in the Southwest Wet Zone and the Kalu Ganga catchment is the most direct conservation action available.