Taxonomy & naming
Hemigrammus barrigonae was described by Carl H. Eigenmann and Arthur Henn in 1914 on the basis of material from South America. The valid name as registered in Eschmeyer's Catalog of Fishes is Hemigrammus barrigonae Eigenmann & Henn, 1914. No subsequently described synonyms are in common circulation.
The genus Hemigrammus is one of the largest and most species-rich characin genera, currently encompassing more than seventy small, typically schooling tetras distributed across tropical South America and into Central America. It is taxonomically turbulent: the genus serves, in practice, as a catch-all for small characins that share a lateral line structure — the scales of the lateral line are perforated on the caudal peduncle but the pore series does not extend the length of the body — but molecular and morphological studies have repeatedly shown the group to be non-monophyletic. A thoroughgoing revision of Hemigrammus and its relatives remains a priority for Neotropical ichthyology, and the standing of several species, including H. barrigonae, may shift as that work advances.
The species epithet barrigonae is a geographic or patronymic reference associated with the type locality material from the Orinoco drainage.
Morphology
Hemigrammus barrigonae is a slender, moderately compressed characin reaching a maximum recorded standard length of approximately 1.5 in. The body plan is typical of the smaller Hemigrammus: a fusiform profile, a moderately deep body that narrows cleanly to the caudal peduncle, a terminal mouth suited to picking small particles from the water column, and the family's characteristic adipose fin between the dorsal and caudal.
The species lacks the bold colour patterns of trade favourites such as H. erythrozonus or Petitella bleheri. Coloration is generally silvery, possibly with a faint lateral stripe or iridescent sheen under good lighting; specific meristic counts and detailed colour descriptions from the original description are not reproduced here. As with most small Hemigrammus, females become noticeably more rounded in the abdomen at maturity, a practical guide to sex in a group. The overall impression is of a trim, schooling fish in the mould of many plain but graceful Orinoco tetras.
Habitat
The species is recorded from the Orinoco River basin, with distribution extending into Colombia and Venezuela and, at least in part of its range, into Brazil via the upper rio Tiquié — a tributary of the upper rio Negro drainage. The IUCN assessment notes occurrence in tributaries and floodplain lakes across this range, and Seriously Fish describes habitat as slow-moving rivers and tributaries.
Water chemistry conditions documented for the species sit comfortably within the soft-to-moderately-hard, weakly acidic parameters typical of Orinoco lowland tributaries: temperature 72–79 °F, pH 5.8–7.0 (with some sources noting as low as 5.5), and hardness up to around 10–12 °dH. At these soft, warm conditions the fish is benthopelagic, occupying the middle and lower water column among vegetation and leaf litter in sheltered, slow-flowing reaches. Its population is described as stable and broadly abundant across much of its range, with no major habitat-wide threats identified.
Feeding
Hemigrammus barrigonae is an omnivore with a trophic level of approximately 3.3, consistent with a diet that balances invertebrate prey with opportunistic plant or detrital material. In the wild it likely takes small aquatic invertebrates, zooplankton, and organic particles from the water column and near the substrate, in the manner of most small schooling characins in Orinoco white- and blackwater tributaries.
In captivity it accepts the standard range of foods suitable for small tetras: high-quality dried flakes and micro-granules as a staple, supplemented with small live or frozen foods such as Daphnia, brine shrimp nauplii, micro-worm, and Cyclops. Variety improves condition and, in breeding groups, brings females into spawning readiness more reliably than a flake-only diet. The fish feeds actively through the water column and does not require bottom-sinking foods, though any that reach the substrate will be investigated.
Mating
No published account of courtship behaviour specific to H. barrigonae is available in the accessible literature. By analogy with well-studied congeners, courtship is presumed to involve males pursuing and displaying to ripe females, likely with fin-spreading and rapid lateral passes through vegetation or spawning areas. In shoaling species of Hemigrammus, group spawning can occur with multiple individuals participating in a single bout, particularly when a group of well-conditioned adults is maintained together.
Females, recognisable by the fuller, rounder abdomen when ripe, are the cue breeders watch for when assessing whether a group is ready to spawn. Conditioning on live and frozen foods typically brings both sexes into reproductive condition within two to three weeks. Spawning is most likely to occur in the early morning hours, as in many egg-scattering characins.
Breeding
Reproductive behaviour has not been formally documented for H. barrigonae, but Seriously Fish notes it is likely similar to other members of the genus: a typical egg-scattering, plant-spawning characin with no parental care and adhesive eggs deposited among fine-leaved vegetation. Based on congener data, eggs are expected to hatch within approximately 24–36 hours at tropical temperatures, with fry becoming free-swimming around three to four days after hatching.
For captive attempts, the standard Hemigrammus breeding setup applies: a small, dimly lit tank with fine-leaved plants such as Java moss or synthetic spawning mops, slightly acidic and soft water in the lower end of the species' temperature range, and a conditioned group or selected pair. Adults should be removed after spawning as they will consume eggs given the opportunity. First foods for the fry are infusoria or commercial liquid fry food, progressing to microworm and newly hatched brine shrimp nauplii as the fry grow. Breeding in captivity has not been widely reported, and the species is uncommon enough in the trade that published accounts are sparse.
In the aquarium
Hemigrammus barrigonae is an undemanding, peaceful community fish suited to a soft-water South American biotope or a general community with compatible tankmates. It is a shoaling species and should be kept in groups of at least six to eight — a larger group produces more natural behaviour and reduces individual stress. A tank of 23.5–31.5 in with gentle filtration, subdued or dappled lighting, and some fine-leaved planting or floating cover replicates the calm, shaded tributaries the species inhabits in the wild.
Water should be maintained in the soft to moderately hard range at pH 5.5–7.0 and 72–79 °F; while the fish tolerates a wider range, soft and slightly acidic conditions bring out its best condition and colour. It is not known to nip fins and poses no threat to similarly sized companions. Peaceful tankmates from the same geographic region — other small Hemigrammus, Moenkhausia, small Corydoras, or dwarf cichlids — work well. The species is not common in the trade and typically enters aquarists' hands as a contaminant in mixed tetra shipments rather than as a targeted purchase; hobbyists who acquire it should treat the group as a collector's item and provide appropriate soft-water conditions from the outset.
Conservation
Hemigrammus barrigonae is assessed as Least Concern (LC) on the IUCN Red List, most recently evaluated in March 2021 and published in the 2023 assessment by F. Lima. The species is considered stable and relatively abundant across its range in the Orinoco basin and upper rio Negro drainage. No large-scale habitat threats are identified; the only noted localised pressure is sewage disposal in parts of its range.
The species is occasionally captured for the international aquarium trade but does not appear to be targeted specifically, and collection pressure is not considered a significant threat at the population level. It is present within some protected areas. The combination of a broad distribution across a major river basin, stable population trend, and absence of targeted commercial harvest supports the Least Concern assessment.