Taxonomy & naming
Hypselobarbus thomassi was described by Francis Day in 1874, with the specific epithet thomassi honouring an individual (likely a British official or collector whose records intersected with Day's survey work in peninsular India). The genus Hypselobarbus was erected by Theodore Nicholas Gill in 1863 for the large South Indian barbs — deep-bodied, fast-river cyprinids of the Western Ghats and Sri Lanka that are distantly related to the true mahseers (Tor) but share their preference for high-gradient, highly oxygenated hill-river habitat.
For much of the twentieth century these fish were lumped into the expanded genus Puntius or alternatively Barbus, the old heterogeneous barb wastebaskets. Pethiyagoda et al.'s comprehensive 2012 revision of South Asian cyprinids reinstated Hypselobarbus as the appropriate genus for this South Indian lineage and removed these species from Puntius; the Catalog of Fishes (Eschmeyer, CAS) follows this placement. Older literature may therefore list this fish as Puntius thomassi.
The species is poorly represented in ichthyological collections and described with significant data gaps; it has no substantive formal revision since Day's original account.
Morphology
Hypselobarbus thomassi is a large barb, with FishBase recording a maximum total length of 39.5 in — placing it in the range of the larger hill-river cyprinids of peninsular India rather than the small ornamental barbs of the aquarium trade. The body form is typical of the genus: moderately deep-bodied and laterally compressed, built for life in fast, turbulent current. The common name "Red Canarese barb" likely reflects a reddish flush on the fins or body of live or breeding fish.
Beyond size and the general cyprinid body plan, detailed morphometric data for this species are sparse in the accessible literature, a reflection of the very small number of voucher specimens that have been studied. A formal morphological comparison with sympatric Hypselobarbus congeners has not been published in widely accessible sources.
Habitat
The species inhabits fast-flowing streams and rivers in the forested foothills and lower slopes of the Western Ghats below the main escarpment, in Karnataka and Kerala. FishBase places it in large streams and rivers below the ghats; the species requires cool, highly oxygenated, turbulent water — the hill-river conditions characteristic of Hypselobarbus as a genus. The two confirmed contemporary populations occupy the Netravathi River and the Kabini River (part of the larger Cauvery catchment).
Water parameters from the Western Ghats hill-river context are consistent with those documented for the species: temperatures of approximately 73–81 °F, pH in the range of 6.0–7.5, and clean, fast-moving water with a high dissolved oxygen content. Substrate is likely coarse sand, gravel, and bedrock — typical of the riverine corridors threading through the Ghats' forested catchments. The species is a benthopelagic river fish, not a lentic or still-water animal.
Feeding
A Kallada River feeding-ecology study provides the most detailed dietary data available for Hypselobarbus thomassi and related congeners. The fish is described as an omnivorous-stenophagic column feeder, meaning its diet, while broad in category, is relatively restricted in practice. The recorded gut-content composition includes diatoms and algae (Bacillariophyceae, approximately 39% of gut content), semi-digested plant matter (approximately 22%), seeds and soil (approximately 16%), and animal matter (approximately 11%), with the remainder attributed to detritus and unidentifiable material.
The gastrosomatic index — a measure of feeding intensity relative to body mass — ranged from 3.28 to 7.33 and peaked between August and November, coinciding with the onset of the breeding season. This pattern of elevated feeding ahead of and during spawning is consistent with the energy demands of gonadal development in a large river barb.
Mating
Like all barbs, Hypselobarbus thomassi is an egg-scattering, non-guarding spawner. There is no parental investment beyond gamete release, no nest construction, and no territory maintained beyond transient courtship activity. The gastrosomatic data suggest spawning activity peaks between August and November, aligned with post-monsoon river conditions that characterise the rivers of the Western Ghats.
In large hill-river barbs and mahseers of this region, courtship typically involves a driving male pressing against a gravid female and the two releasing eggs and milt together in fast-flowing water or over coarse substrate. Adhesive or semi-adhesive eggs settle among gravel and submerged structure. No courtship or mating observation has been formally published for this species specifically.
Breeding
As an egg-scattering cyprinid, Hypselobarbus thomassi deposits adhesive eggs over substrate or among submerged material with no subsequent parental care; adults do not guard, attend, or provision eggs or larvae. The feeding ecology data pointing to a seasonal peak in gut fullness from August through November places spawning in the Western Ghats post-monsoon season, when river flows are elevated and water temperatures remain within the species' preferred range.
No captive breeding has been documented for this species in the accessible literature — a consequence of its extreme rarity, limited distribution, and near-absence from the aquarium trade. Reproductive biology details (fecundity, egg size, larval development period) remain undescribed.
In the aquarium
Hypselobarbus thomassi is not an aquarium fish in any practical sense. Reaching up to 39.5 in total length, it is far larger than a home aquarium can reasonably accommodate, and there are no records of it being kept or bred in captivity. It does not appear in the ornamental trade and, given its Critically Endangered status and severely restricted wild range, should not be sought for private collection.
For fishkeepers drawn to large Indian barbs, related but less critically threatened members of the genus Hypselobarbus — and mahseer relatives in the genus Tor — are occasionally maintained in public aquaria or large zoological facility tanks with appropriate permits. The Red Canarese barb is a species of conservation significance, not an aquarium subject.
Conservation
Hypselobarbus thomassi is assessed as Critically Endangered (CR) on the IUCN Red List, assessed in 2013 and published in the Journal of Threatened Taxa. It is among the most critically threatened freshwater fish in the Indian subcontinent. Its known occupied area is estimated at less than 6 mi² across just two severely fragmented locations — the Netravathi River (Karnataka) and the Kabini River within the Cauvery catchment — and only one specimen was recorded from the Netravathi in recent field surveys, indicating population collapse in that locality.
The threats driving its decline are those common across the Western Ghats fish fauna: dam construction and river impoundment (which disrupt the fast-flowing, well-oxygenated conditions the species requires), sand mining, water extraction for agriculture and urbanisation, and pollution from agricultural runoff and domestic sewage. The Western Ghats freshwater hotspot has seen severe modification of its river systems, and the larger-bodied cyprinids requiring unimpeded hill-river corridors are among the most exposed.
The India Biodiversity Portal carries a species profile confirming its endemic Western Ghats distribution and Critically Endangered status. Given the data gaps in its taxonomy, distribution, and biology, targeted field surveys and formal conservation assessments are needed to determine whether viable populations persist and where any remaining habitat might be protected.