Taxonomy & naming
Hemibrycon paez was described by César Román-Valencia and Diego Arcila-Mesa in 2010 in a paper published in the Revista de Biología Tropical, in which five new Hemibrycon species from the Río Magdalena basin were formally recognised. The type locality is La Topa Creek, a tributary of the Río Páez, at approximately 2°30'01"N, 75°58'06"W, elevation 1,574 ft, in the municipality of Puerto Valencia, Inzá, Cauca Department, Colombia. The original description is based on a sample of 40 specimens.
The valid name, following Eschmeyer's Catalog of Fishes, is Hemibrycon paez Román-Valencia & Arcila-Mesa, 2010. The genus Hemibrycon belongs to the family Characidae and represents a group of medium-sized, silvery characids distributed across the river systems of the northern and central Andes. Relationships within the genus have not been resolved into a stable phylogenetic framework, and the number of valid species remains subject to ongoing revision.
FishBase records the family placement as Stevardiinae within a broader concept of Characidae; the IUCN assessment and the original description treat it under Characidae. The specific epithet refers to the Río Páez, the drainage system from which the type series was collected, and by extension honours the indigenous Páez (Nasa) and Guambiano peoples inhabiting the Cauca region at the type locality.
Morphology
Hemibrycon paez reaches a maximum recorded standard length of 3.5 in. Like other members of the genus it is a moderately elongate, laterally compressed fish with the typical characid body plan: a forked tail, a small adipose fin, and a single dorsal fin positioned roughly mid-body.
The species is distinguished from congeners in the Magdalena basin by a combination of meristic characters: lateral line scales numbering 39–42 (compared with 43–54 in related species), scales between the lateral line and the anal-fin origin 6–7 (versus 4–5 in close relatives), scales between the lateral line and the dorsal-fin origin 6–7, and anal-fin rays 19–23 (versus 23–29 in related species). An additional diagnostic feature noted in the original description is that the mesopterygoid barely contacts the metapterygoid, a condition differing from the firmer articulation seen in congeners.
Detailed coloration in life is not documented in the available literature; the species is presumed to carry the generally silvery to pale flanks with a lateral stripe typical of Hemibrycon, but specific colour notes from the original description are not available in the sources consulted.
Habitat
The only confirmed habitat for Hemibrycon paez is La Topa Creek in the upper Río Páez drainage, a high-Andean tributary of the upper Magdalena River basin in Cauca, Colombia, at an elevation of approximately 1,574 ft. The IUCN assessment describes the habitat as rivers and creeks with clean, clear water over substrates of stone, sand, and organic material.
FishBase records water temperatures of 66–70 °F at the collection site, consistent with the cool, well-oxygenated conditions typical of Andean piedmont streams. Field measurements cited in the FishBase record indicate surface temperatures of 67–69 °F, dissolved oxygen of 7.6–8.0 mg/L, and clear water. These cool-water conditions reflect the elevation of the type locality and distinguish H. paez from lowland Hemibrycon species that inhabit warmer river systems.
Beyond the type locality, no additional populations have been confirmed. The IUCN notes that the distribution may be broader than currently documented, but the species is known with certainty only from its original collection site in Inzá municipality.
Feeding
No dedicated dietary study of Hemibrycon paez has been published. Members of Hemibrycon are generally considered omnivorous opportunists, consuming invertebrates, small aquatic insects and larvae, organic detritus, and plant material. The clear, fast-flowing Andean creek habitat of H. paez is likely rich in aquatic insect larvae and other benthic invertebrates, which probably form a significant component of the natural diet.
In the aquarium, Hemibrycon species typically accept a range of prepared foods including quality flake and small pellets, along with frozen and live invertebrate foods such as bloodworm, Daphnia, and brine shrimp. A varied diet that includes live or frozen components is recommended for conditioning and long-term health, though species-specific feeding behaviour for H. paez has not been studied.
Mating
No direct observations of courtship or mating behaviour in Hemibrycon paez have been published. Within Hemibrycon and the broader subfamily Stevardiinae, reproductive strategies tend toward open-water or substrate egg-scattering with no parental care. Spawning is typically associated with fine-leaved aquatic vegetation or other fine substrate where adhesive or semi-adhesive eggs can be deposited.
Sexual dimorphism in Hemibrycon commonly takes the form of females becoming noticeably deeper-bodied when ripe, and males may display minor fin differences, but specific information for H. paez is not documented in the available sources. Given the cool temperatures of the type locality, any seasonal spawning in the wild may be triggered by changes in rainfall or temperature characteristic of the Andean wet season.
Breeding
Hemibrycon paez has not been bred in captivity under documented conditions. General expectations for the genus suggest egg-scattering open spawning behaviour typical of characids: adults would release and fertilise small adhesive eggs among fine-leaved plants or over a suitable substrate, with no subsequent parental attention and a tendency for adults to consume their own spawn if given the opportunity.
Breeding in captivity, if attempted, would likely benefit from replicating the cool, well-oxygenated water conditions of the type locality — temperatures in the 66–70 °F range and high dissolved oxygen. The absence of hobby records reflects the species' rarity in the trade rather than any known difficulty in breeding.
In the aquarium
Hemibrycon paez is essentially absent from the aquarium hobby. The species has not been exported commercially to any documented degree, and no established husbandry guidelines exist. Based on the conditions of its type locality and its relationship to other Hemibrycon, any care recommendations are inferential.
If specimens were available, a setup mimicking cool, clear, well-oxygenated Andean stream conditions would be appropriate: temperatures of approximately 66–70 °F, good water movement and filtration, and a substrate of sand or fine gravel with some rocks and plant cover. As a mid-sized characid, a spacious tank with open swimming space and a shoal of conspecifics would likely reduce stress. The species would be unsuitable for the typical warm tropical community tank given its cool-water origins.
Conservation
Hemibrycon paez is assessed as Data Deficient (DD) on the IUCN Red List, with the assessment published in 2016 based on an evaluation conducted in October 2014. The DD listing reflects the fact that the species is known from a single type locality in the upper Magdalena basin and that insufficient information is available to determine whether it qualifies for a threatened category.
The IUCN assessment notes that the species is endemic to Colombia and currently known only from La Topa Creek in the Inzá municipality of Cauca. Its status in protected areas is unknown, no conservation measures are in place, and the nature and extent of any threats have not been established. The assessment calls for research into the species' distribution, population size, trends, and potential threats as priorities before a more definitive red-list status can be assigned.
The upper Magdalena basin faces ongoing pressures from agricultural expansion, deforestation, and water extraction across much of its extent. Whether these pressures affect the specific localities where H. paez occurs is unknown given the lack of survey data.