Taxonomy & naming
Cyclocheilichthys repasson was described by the Dutch ichthyologist Pieter Bleeker in 1853 from material collected in Sumatra — the type locality is given as Pangabuang, Lampung Province — and the species has historically been shuffled between several genus-level arrangements. It has appeared in the literature as Cyclocheilichthys repasson, a combination still used by some contemporary sources including Seriously Fish, and older catalogue entries placed it in or near Barbus. The Catalog of Fishes (Eschmeyer, CAS) is the authority for valid names, and the combination Cyclocheilichthys repasson is followed here; the parenthetical authority marks the move out of Bleeker's original genus.
A dietary field study by Sangpradub et al. (2010) from Kaeng Lawa, Thailand confirmed the species' presence in mainland rivers under the name Cyclocheilichthys repasson (Bleeker, 1853) and analysed its food overlap with the glass catfish Ompok bimaculatus in the same system. The genus Anematichthys is a grouping of medium-to-large Southeast Asian cyprinids; the broader Cyclocheilichthys complex from which it was separated has a complicated taxonomic history, and the nomenclatural status of some populations across the wide range remains subject to revision.
This fish was long listed as Anematichthys repasson; Eschmeyer's Catalog of Fishes places the species in Cyclocheilichthys, and the current combination Cyclocheilichthys repasson is followed here.
Morphology
Cyclocheilichthys repasson is a moderately deep-bodied, laterally compressed cyprinid with the typical barb body plan — a blunt snout, subterminal mouth, and scales that grade from large on the flank to smaller toward the fin bases. FishBase gives a maximum size of 11 in SL, consistent with a mid-sized lowland river barb, though Seriously Fish notes that Indochina populations tend to plateau around 6.3 in SL while Indonesian specimens may approach 11.02 in, suggesting some regional variation or the involvement of more than one population unit under the current name.
Detailed meristic and coloration data for wild-caught specimens are not well documented in the hobbyist or popular literature, reflecting how rarely this species enters the trade. The fish is a benthopelagic species found from mid-water down to bottom levels and is likely silvery to pale yellow-brown on the flank in the typical manner of large generalist barbs, without dramatic banding or spots.
Habitat
Across its range — the Mekong and Chao Phraya drainages, the Malay Peninsula, Sumatra, Java and Borneo — Cyclocheilichthys repasson occupies a broad spectrum of lowland freshwater habitats: small rivers, canals, ditches, ponds, reservoirs and swampy backwaters, as well as medium to large river channels. Seriously Fish describes a preference for slower-moving or still zones with submerged roots, biofilm and floating or broad-leaved aquatic plants such as Microsorum, Taxiphyllum and Cryptocoryne, while the WWF Mekong report records the wider basin fish fauna using shallow floodplain zones for feeding and spawning.
Water chemistry across the range is soft to moderately hard and mildly acidic to neutral. FishBase records a pH of 6.5–7.0, temperature around 77 °F and hardness of approximately 5 dGH for the species, while Seriously Fish gives a broader tolerance of 68–79 °F, pH 5.0–8.0 and hardness 18–357 ppm, reflecting the range of conditions encountered from peat-influenced blackwater swamps in Sundaland to more turbid mainland rivers. The WWF Mekong survey documents mean water temperatures of approximately 76 °F and pH near 7 with soft to moderate hardness in the Mekong basin.
Feeding
Cyclocheilichthys repasson is chiefly predatory in the wild, taking insects, crustaceans and molluscs, with algae and plant material also recorded in gut contents. Seriously Fish characterises it as a confident opportunist suited to live and frozen foods — bloodworm, Daphnia and Artemia are accepted — as well as dried flakes in captivity. The Sangpradub et al. (2010) field study from Kaeng Lawa, Thailand analysed seasonal food habits and dietary overlap between this species and Ompok bimaculatus in the same river, confirming a varied diet that shifts with seasonal availability.
In the aquarium Seriously Fish recommends small live and frozen invertebrate foods as the core of the diet, supplemented with quality dried foods. The species' predatory tendencies should be factored in when selecting tankmates — very small fishes or invertebrates may be at risk with larger individuals.
Mating
Like all barbs, Cyclocheilichthys repasson is an egg-scattering, non-guarding spawner. No nest is built, no pair bond is maintained beyond the spawning act, and neither parent defends eggs or fry. Seriously Fish notes that in the wild this species spawns in flooded zones at the end of the wet season, a pattern typical of lowland tropical barbs that exploit rising water levels and the temporarily available shallow, vegetated habitat for reproduction.
Courtship follows the standard barb pattern in which a driving male pursues a gravid female through vegetation or over the substrate, the two fish pressing briefly together as eggs and milt are released simultaneously. Adhesive eggs settle among plants or onto the bottom, after which the adults disperse and take no further interest in the spawn.
Breeding
Cyclocheilichthys repasson has not been bred in captivity according to available records, and Seriously Fish explicitly notes that captive breeding has not been achieved. In the wild, spawning is tied to seasonal flooding and the availability of shallow vegetated zones at the close of the wet season — conditions that may be difficult to replicate reliably in an aquarium setting.
Should captive breeding be attempted, the approach used for other medium-to-large barbs would be a logical starting point: a spacious, well-planted tank with soft, slightly acidic water and a temperature in the lower part of the species' range to condition the fish, followed by a gradual warming and increase in live foods to trigger spawning behaviour. Eggs are adhesive, scattered among plants or onto the substrate, and are likely to be consumed by the adults if not separated promptly. No data on incubation times or larval development are available in the published literature.
In the aquarium
Cyclocheilichthys repasson is a rare find in the aquarium hobby and is not considered a routine trade species. Seriously Fish notes it is gregarious and should be kept in groups of at least six, in a spacious aquarium that reflects its natural habitat: areas with submerged root tangles, broad-leaved plants and floating vegetation, soft to moderately hard water, and a temperature of 68–79 °F at broadly neutral to slightly acidic pH.
Its predatory tendencies mean that very small fishes and invertebrates should not be mixed with larger individuals. Its size range — up to 11 in SL in larger river populations, though Indochina fish may remain around 6.3 in — means that tank sizing must account for potential adult length. Good filtration and regular water changes are advisable given that larger cyprinids are heavy feeders. The species' rarity in the trade means that wild-caught specimens are the likely source, and careful acclimation to captive conditions is recommended.
Conservation
Cyclocheilichthys repasson is listed as Least Concern (LC) on the IUCN Red List. Its wide distribution across the Mekong and Chao Phraya basins, the Malay Peninsula, Sumatra, Java and Borneo provides a broad range without evidence of major population-level decline across all populations collectively.
Nonetheless, the pressures on lowland freshwater habitats across Southeast Asia are significant. The Mekong basin faces hydropower development, sand extraction and altered flood pulses that reduce the shallow seasonal floodplain zones this species uses for spawning. In Sundaland — Sumatra, Java and Borneo — deforestation, peat-swamp drainage, pollution and conversion of riverine habitat to agriculture and aquaculture threaten the fish fauna broadly. The species' relatively wide tolerance of water chemistry offers some resilience, but continued habitat degradation in the lowland river systems it depends on is a legitimate long-term concern even for an LC-listed taxon.