Taxonomy & naming
Hemibrycon guejarensis was formally described in 2018 by César Román-Valencia, Raúl Ruiz-C., and Donald C. Taphorn. The Catalog of Fishes (Eschmeyer, CAS) records the valid name as Hemibrycon guejarensis Román-Valencia, Ruiz-C. & Taphorn, 2018. The type locality is Pringamosal Creek, Blanco River system, Vista Hermosa County, Meta Department, Colombia. The species belongs to the genus Hemibrycon, a diverse Neotropical lineage within the broad family Characidae.
FishBase places Hemibrycon within the subfamily Hemibryconinae (family Stevardiidae under the updated classification used by that database), reflecting ongoing revision of characoid higher taxonomy; however, Catalog of Fishes and this atlas treat the family as Characidae, the framework currently applied across the genus. The specific epithet guejarensis is a New Latin toponym referring to the Güejar River Basin — the type locality's broader drainage system — following the standard practice of honouring geography in the names of locally endemic species.
Diagnostic meristic features that separate H. guejarensis from its closest congeners include a dorsal-fin ray count of ii,7,i, distinguishing it from H. jabonero and H. taeniurus, which carry ii,8 dorsal-fin rays. The species also shows a wider second pigment layer in the humeral spot (three scale widths versus two in related species) and pectoral fins long enough that the tip passes the pelvic-fin insertions — a character that differs from H. metae, in which the pectoral fin falls short.
Morphology
Hemibrycon guejarensis is a slender, laterally compressed characid of modest size. The maximum recorded standard length is 3 in (approximately 3.1 in), recorded from a female specimen. The body plan is typical of the genus: a relatively elongate form with a well-developed humeral spot — a dark blotch behind the gill cover — that provides one of the key identification marks used in species-level diagnoses.
The dorsal-fin formula of ii,7,i and the extent of the pectoral fins (reaching or passing the pelvic-fin insertions) are the hard morphological characters that anchor the species diagnosis. The wider second pigment layer in the humeral spot — spanning three scale widths rather than the two seen in close relatives — is a consistent feature noted in the original description. Live or freshly preserved coloration details for this species are not well documented in the available literature; like most Hemibrycon, the fish is likely silvery overall with the dark humeral marking and perhaps a faint caudal spot or lateral stripe, but precise colour notes beyond these basics are sparse in the cited sources.
Habitat
Hemibrycon guejarensis is known exclusively from the Güejar River Basin in Meta Department, Colombia, situated in the Serranía de La Macarena foothills and draining into the upper Guaviare River, itself a tributary of the Orinoco system. The IUCN assessment describes the habitat as mountain and piedmont streams with gravel, rock, or sandy substrates, and water that is clear, well-oxygenated, and of high transparency.
FishBase notes that the species is collected along stream shores over sandy substrates in tributaries with tea-coloured (humic) water — a minor discrepancy with the IUCN's description of clear water that may reflect variation among collection sites or across seasons. The species is benthopelagic in habit, occupying the lower and mid-water zones of these streams. Sympatric species recorded in the same collections include Astyanax spp., Bryconamericus macarenae, Creagrutus maculosus, Characidium cf. zebra, and Hemigrammus barrigonae — a community of small to mid-sized characoids characteristic of Orinocan piedmont drainages.
The Serranía de La Macarena is a UNESCO-designated biosphere reserve and a nationally protected area in Colombia, which means at least a portion of the species' known range falls within formal conservation boundaries.
Feeding
Hemibrycon guejarensis is classified as an omnivore by the IUCN assessment, with a diet comprising invertebrates and plant material obtained from the water surface or drifting downstream in the current. FishBase assigns a trophic level of 3.0 (± 0.4), consistent with a generalist carnivore-omnivore that takes invertebrates as a primary protein source alongside incidental plant and detrital matter.
As with most small Hemibrycon, the fish is presumed to forage opportunistically on drifting aquatic and terrestrial insects, small crustaceans, and whatever organic matter the mountain stream current delivers. Detailed dietary studies specifically for this species are not documented in the available literature beyond these broad categories.
Mating
No dedicated reproductive behaviour studies have been published for Hemibrycon guejarensis specifically. By analogy with other members of the genus and the broader Characidae, the species is presumed to be an egg-scatterer practicing open spawning with no parental care — the default mode for most small characids. In typical characid spawning, a gravid female is pursued by one or more males, and eggs are released and fertilised while the pair or group moves through vegetation or along the substrate, with adhesive or semi-adhesive eggs settling among fine-leaved plants or substrate debris.
The generation length recorded by the IUCN is approximately two years, which provides some indirect evidence about the pace of sexual maturation and turnover within the population. The species is described as non-migratory and congregatory year-round, suggesting it does not undergo the upriver spawning migrations seen in some larger characids.
Breeding
Hemibrycon guejarensis has not, to this atlas's knowledge, been established in the ornamental aquarium trade or bred in captivity in any documented way. Accordingly, no husbandry-based breeding data are available. The presumed mode — egg-scattering open spawning among fine-leaved plants or over substrate, with adhesive eggs and no parental care — follows the shared plan of most small Hemibrycon and related characids.
The IUCN's generation length estimate of approximately two years implies a lifespan and maturation schedule similar to other small South American stream characids: likely reaching sexual maturity within the first year under favourable conditions, with adults potentially living two to three years in the wild. Stream temperature in the Serranía de La Macarena foothills, which influences egg incubation rates, is not documented in the available sources for this species.
In the aquarium
Hemibrycon guejarensis is not an established aquarium species and is not available through the ornamental fish trade as far as is documented. Its small size (under 3 in SL), presumed peaceful and schooling temperament, and origin in clear, well-oxygenated Colombian piedmont streams suggest it would be manageable in a species-appropriate aquarium if it were ever collected for the hobby — but this is speculative.
For any wild-collected specimen, water conditions should reflect the natural habitat: cool to moderate tropical temperatures, good oxygenation, and clean water with relatively low organic load, consistent with fast-flowing Andean foothill streams. The species has a fishing vulnerability score of 10 out of 100 (FishBase), indicating it is not considered susceptible to overfishing at present levels — a reflection of its small size and limited commercial interest rather than abundance.
Conservation
The IUCN Red List assessed Hemibrycon guejarensis as Least Concern (LC) in November 2020 (published 2021), with a population trend recorded as stable. The assessment notes that the species is known only from the Güejar River Basin in Meta Department — a restricted range that does not itself qualify the species for a threatened category given the apparent stability of the population and the partial protection afforded by the Serranía de La Macarena protected-area complex, within which 1–10% of the population is estimated to occur.
Potential threats identified include small-scale agriculture and cattle ranching in the surrounding landscape, though their actual impact on the species is described as unknown. The IUCN flags research needs across the board: distribution limits, life history, ecology, and threat severity are all poorly known. A species confined to a single river basin in a region of active agricultural expansion warrants monitoring even under a Least Concern status, and the assessors recommend further field study to close these data gaps.