Taxonomy & naming
Hemigrammus aguaruna was formally described by Flávio C. T. Lima, Claudia Correa and Renata P. Ota in 2016 as a new species of the genus Hemigrammus Gill, 1858, in the family Characidae. The type locality is given as tributaries of the Río Marañón in Departamento Loreto, northwestern Peru; the species has also been recorded from Colombia, placing it in the westernmost reach of the Amazon drainage. The original description was published as part of a broader revision of western Amazon Hemigrammus.
A subsequent phylogenomic study of the Characidae family (Melo et al. 2024) placed the species in the resurrected genus Holopristis, and some current taxonomic treatments recognise it as Holopristis aguaruna. Eschmeyer's Catalog of Fishes (the authority for valid names on this site) is the court of last appeal for the currently accepted combination; the genus assignment used here reflects the Lima et al. 2016 original description under which the species is most widely cited.
The specific epithet aguaruna refers to the Awajún (Aguaruna) people, an indigenous group of the Peruvian Amazon whose territory overlaps much of the Río Marañón headwaters region from which the species was first collected.
Morphology
Hemigrammus aguaruna is a small, slender tetra, with specimens in the type series measured at 1 in standard length. Like other members of Hemigrammus, it has the typical characid body plan: a moderately compressed, fusiform profile, a forked tail, and a small adipose fin between the dorsal and caudal fins.
Detailed colour pattern and meristic data are documented in the original description. The combination of proportional and pigmentation characters that distinguish it from congeners is set out in the 2016 paper; in life, small Hemigrammus from terra firme forest streams in Loreto often show subdued silvery or translucent coloration with variable dark lateral markings, reflecting the tannin-stained, low-light conditions of the understorey streams they inhabit. Data on maximum size in aquarium conditions are not available from published sources.
Habitat
The type series was collected from tributaries of the Río Marañón in Loreto, Peru, a region of western Amazonian lowland forest. Additional specimens have been recorded from Colombia, confirming the species occurs across the Colombia–Peru border in the western Amazon basin, including the Río Morona and Río Corrientes drainages.
Measured water parameters from the type locality include a pH of 6.83 and a temperature of 80 °F (79.7 °F), consistent with soft, slightly acidic blackwater or clearwater streams under terra firme (non-flooded upland) forest canopy. Terra firme streams in Loreto are typically shaded, with low conductivity, soft substrate, submerged leaf litter, and root tangles providing cover for small characids. The species has been noted in regional checklists as having a restricted distribution within Loreto, Peru.
Feeding
Gut-content analysis of type series specimens revealed a diet dominated by small aquatic and terrestrial arthropods, including Diptera larvae and other aquatic insects. This is typical for small Hemigrammus inhabiting forest streams, where fallen terrestrial invertebrates supplement the aquatic prey available in shaded, low-productivity headwaters.
In captivity, small insectivorous tetras from Amazonian forest streams generally accept a range of prepared and live foods. Newly hatched brine shrimp, micro-worms, Daphnia, and finely crushed flake or micropellets are appropriate if the species is ever maintained in aquaria. A diet with a meaningful live or frozen invertebrate component is recommended to mirror the natural prey spectrum.
Mating
No direct observations of mating behaviour in Hemigrammus aguaruna have been published. Based on the reproductive biology of the broader genus and related Amazonian characids, the species is presumed to be an egg-scattering open spawner without parental care. Males in breeding condition likely display to females with fin erection and lateral posturing, as is typical for small tetras.
Reproductive seasonality in terra firme forest streams in Loreto may be influenced by the local hydrological cycle, with spawning activity potentially timed to rising water levels that cue breeding in many Amazonian characids.
Breeding
Fecundity data from the original description indicate approximately 136 oocytes in examined females, giving a baseline estimate of clutch size. This is within the range expected for a small Hemigrammus and is consistent with egg-scattering reproductive strategies typical of the genus, in which adhesive eggs are deposited among fine-leaved aquatic plants or root tangles and then abandoned.
No captive breeding records for H. aguaruna are available in the published or hobby literature examined. By analogy with well-studied congeners, incubation at temperatures around 79–82 °F (79–82 °F) would be expected to produce free-swimming fry within several days of fertilisation, with fry requiring infusoria or similarly fine first foods before graduating to nauplii. Parental care is not expected.
In the aquarium
Hemigrammus aguaruna is not currently an established aquarium species and is rarely if ever encountered in the hobby trade. Its small adult size (under 1.5 in SL), forest-stream origins, and insectivorous diet place it in a category of micro-tetras that can be maintained successfully in small to medium biotope-style aquaria replicating the Loreto terra firme stream environment: soft, slightly acidic water at around 79–82 °F (79–82 °F), dim or diffuse lighting, leaf litter substrate, fine-leafed plants or root tangles, and minimal water movement.
Should specimens become available through scientific collection or specialist importers, a group of six or more individuals is advisable to reduce stress and allow natural shoaling behaviour. Tankmates should be similarly sized and non-aggressive; small South American characids, Corydoras, and small apistogramma are natural companions from the same biome. Live and frozen invertebrate foods would form the core of the diet.
Conservation
Hemigrammus aguaruna has not been evaluated by the IUCN Red List and carries no formal conservation status as of 2026. It was noted in a checklist of freshwater fishes from Loreto, Peru as a species with a restricted distribution in the region, which signals a degree of endemism that could make it vulnerable to habitat disturbance in the Río Marañón tributaries.
The western Amazon basin in Loreto is subject to growing pressure from petroleum extraction, road development, and forest clearance, all of which degrade the small forest streams this species inhabits. Without a formal range assessment or population data, the conservation needs of H. aguaruna remain poorly understood. Its recent description (2016) means it has had limited time to accumulate the distributional records that would support an IUCN assessment, and a concerted survey effort in its known localities would be the first step toward understanding its status.