Taxonomy & naming
Pethia reval was described by Meegaskumbura, Silva, Maduwage and Pethiyagoda in 2008 in Ichthyological Exploration of Freshwaters (volume 19, issue 2), originally placed in the old omnibus genus Puntius as Puntius reval. The species had long been exported from Sri Lanka as a colour form of Pethia cumingii, and the formal separation in 2008 clarified a distinction that aquarists had sometimes suspected but lacked a scientific name to attach to it.
In 2012, Pethiyagoda and colleagues published a partial review of South Asian small barbs (Ichthyological Exploration of Freshwaters 23(1):69–95) that erected the genus Pethia to accommodate a cluster of species removed from Puntius. The genus Pethia is diagnosed by the absence of rostral barbels, minute or absent maxillary barbels, a stiff serrated last unbranched dorsal-fin ray, a black blotch at the caudal peduncle, and a deep third infraorbital bone that partially overlaps the preoperculum. Under the Catalog of Fishes the current valid combination is Pethia reval (Meegaskumbura, Silva, Maduwage & Pethiyagoda, 2008), with the parenthetical authority marking the transfer out of Puntius.
The species name is drawn from Sinhala: "reval" combines the elements for red and fins, a direct reference to the species' most conspicuous field mark. A naturalized hybrid population between P. reval and P. cumingii has been documented in the southern part of the range, suggesting the two species come into secondary contact where their distributions overlap.
Morphology
Pethia reval is a small, laterally compressed barb. Males reach a maximum standard length of about 1.5 in; FishBase records a maximum of 1.5 in SL for males. The body is silvery, and two vertical dark bars punctuate the flanks: one positioned immediately behind the gill cover and one above the anal-fin base. A black blotch at the caudal peduncle is characteristic of the genus Pethia. The lateral line is incomplete, running over only 4–9 scales rather than the full flank.
The most striking feature is the coloration of the fins. All unpaired fins — the dorsal, caudal and anal — are suffused with red to orange-red, and the red extends into the pectoral and pelvic fins. The leading edge of the dorsal fin carries the stiff, serrated last unbranched ray typical of Pethia. Barbels are absent or rudimentary, as in the rest of the genus.
Sexual dimorphism is moderate. Males are smaller, slimmer and develop more intense red pigment in breeding condition. Females are larger, with a deeper, rounded abdomen when gravid. The species bears a superficial resemblance to P. cumingii, but the red fin coloration in P. reval is more extensive and saturated; the two were long confused in the trade.
Habitat
Pethia reval is endemic to western Sri Lanka, where it is known from the Kelani, Maha Oya, Attanagalu and Kalu river basins — all draining the island's wet zone. The type locality is the Kelani River basin at Labugama, at approximately 295 ft elevation. The IUCN assessment records an Extent of Occurrence of 2,347 mi² and an Area of Occupancy of 92–107 mi².
The species is presumed to occupy smaller tributaries and headwater streams rather than the main river channels. Habitat is permanent rivers and streams of up to 7 ft depth with sandy or rocky substrates (not muddy bottoms). Water conditions recorded by Seriously Fish are 64–79 °F, pH 6.0–7.5 and hardness 36–215 ppm; the IUCN notes an optimal temperature range of 79–81 °F for the species. These are soft to moderately hard, near-neutral waters — typical of upland and foothill streams in Sri Lanka's wet zone.
A naturalized introduced population has been recorded in the Kandy area, outside the species' natural coastal-plain range. The four known locations fall within the Gampaha, Colombo and Kegalle districts.
Feeding
In the wild, Pethia reval is an opportunistic omnivore. FishBase records the diet as including diatoms, algae, detritus, aquatic insects, crustaceans and zooplankton — a broad feeding strategy consistent with other small benthic and benthopelagic Pethia species browsing the substrate surface and water column of shallow streams.
In the aquarium the species is undemanding. Keepers report acceptance of live and frozen foods such as bloodworm, Daphnia and Artemia, supplemented with quality flake or micro-pellet. Providing a varied diet enhances the red pigmentation. Being a small, active barb, it feeds throughout the day in small bouts rather than in concentrated ambush strikes.
Mating
Like all barbs, Pethia reval is an egg-scattering, non-guarding spawner. Spawning in the wild is unrecorded in the scientific literature, but the mating behaviour is presumed to follow the pattern universal in Pethia and the wider barb clade: a gravid female is pursued by one or more males through fine-leaved vegetation or over the substrate, and eggs and milt are released together in brief lateral presses.
No pair bond forms, and neither sex guards a territory beyond the transient courtship pursuit. Males in breeding condition display their most intense red coloration during courtship. The scattered adhesive eggs settle among plants or onto the bottom; adults do not attend them and will eat them if given the opportunity. No nest, bubble-nest, mouthbrooding or parental care of any kind is known or expected in this genus.
Breeding
Captive reproduction of Pethia reval has not been formally documented in the scientific literature; Seriously Fish notes that reproduction is "unrecorded" in its profile. Given the species' conservation status and the potential for captive breeding to relieve collection pressure, this represents both a gap in knowledge and an opportunity for dedicated aquarists.
The general approach for related Sri Lankan Pethia species would apply: a separate, shallow spawning tank with soft, mildly acidic water, fine-leaved plants or a spawning mop, and a substrate mesh to protect eggs from adults. A well-conditioned pair would be introduced, spawning expected in the morning, and adults removed promptly afterward. Eggs of small barbs typically hatch within one to two days at optimal temperature, with fry becoming free-swimming a few days later and accepting infusoria followed by newly hatched brine shrimp. Given the species' Endangered status, any successful captive breeding records would be of scientific as well as practical value.
In the aquarium
Pethia reval has been exported from Sri Lanka as an ornamental fish for many years, historically under the name of P. cumingii. Seriously Fish recommends keeping it in groups of six to ten or more: like other small barbs, it is a peaceful shoaling species that is more secure and less stressed in numbers, and shoaling behaviour is most natural when groups are large enough to sustain an internal social dynamic.
The species suits a well-filtered aquarium with clean, oxygen-rich water in the range of 64–79 °F and a broadly neutral to slightly acidic pH (6.0–7.5). Its Sri Lankan stream habitat suggests moderate current and good oxygenation are beneficial. A planted tank with shaded areas and open swimming space suits it well. Long-finned or very slow tankmates are best avoided; active, similarly sized companions are preferable. The small size means it should not be kept with anything large enough to regard it as food.
Because wild-caught individuals drive the trade and the species is Endangered, sourcing from reputable captive-breeding operations or aquarists who have bred it domestically is strongly encouraged. Hobbyists keeping this species contribute meaningfully to its conservation prospects simply by maintaining and attempting to breed it in captivity.
Conservation
The IUCN Red List lists Pethia reval as Endangered under criteria B1ab(iii,v)+2ab(iii,v), assessed on 7 August 2019 (published 2019; errata 2020). The Extent of Occurrence is 2,347 mi² and the Area of Occupancy is 92–107 mi², covering four known locations in the Gampaha, Colombo and Kegalle districts of western Sri Lanka. The population trend is decreasing.
The species faces an unusually dense stack of threats. Hydropower development in the Kelani basin alters river flow, temperature and turbidity, disrupting the clear, well-oxygenated upland streams the species occupies. Logging, rubber and tea plantation expansion, and gem mining cause sedimentation and riparian degradation. Domestic and agricultural pollution — runoff, pesticides, effluent — further degrades water quality. Concrete road crossings and weirs fragment stream networks, isolating populations. Twelve invasive alien fish species had been established in Sri Lanka as of 2016, five rated as seriously invasive, and their competitive and predatory effects on endemic small barbs like P. reval are a growing concern.
Ornamental export has contributed to pressure on the species: in 2005, 7,891 individuals were exported from Sri Lanka under the name Pethia cumingii, of which 98% were wild-caught; the exact proportion attributable to P. reval is unknown but non-trivial. Export of the species is not currently prohibited, and legislation protecting freshwater fish habitats is poorly enforced. Much of the species' range falls outside protected areas, and no major captive-breeding programme was in place at the time of the IUCN assessment. Flash flooding driven by changing rainfall patterns adds a further climate-linked threat.