Taxonomy & naming
Hemigrammus aereus was described by the French ichthyologist Jacques Géry in 1959. The type locality is the Comté River basin in French Guiana, northeastern South America. The holotype, catalogued as MHNG 2181.86, measures 1 in standard length and is deposited in the Muséum d'Histoire Naturelle de Genève. Eschmeyer's Catalog of Fishes (Catalog of Fishes, CAS) records the valid name as Hemigrammus aereus Géry, 1959.
Recent phylogenetic revisions of the family Characidae have reorganised many genera traditionally placed within it; some taxonomic frameworks now allocate Hemigrammus to a broader or rearranged grouping. The top-level family assignment in this atlas follows the traditional and widely used Characidae, which remains in common usage for the genus in the literature and in reference databases. The status of H. aereus as a valid species is confirmed by recent (2025) taxonomic treatments of French Guianan ichthyofauna.
Morphology
Hemigrammus aereus is a very small tetra, reaching a maximum recorded standard length of approximately 1 in. The holotype measured 1 in SL, indicating that adult size is close to this figure. Like other members of the genus, it is presumed to be a laterally compressed, fusiform characid of broadly tetra-like proportions, with the adipose fin characteristic of the family.
Detailed morphological data for this species are sparse in the publicly available literature. The specific epithet aereus (Latin: bronze, brassy) likely alludes to a bronzy or coppery tone in the body colouration, a feature common to several small Hemigrammus species from Guianan drainages. Precise meristic counts and a full description of patterning await wider documentation in English-language ichthyological literature.
Habitat
Hemigrammus aereus is known from the Comté River basin of French Guiana, a coastal drainage of the Guiana Shield flowing northward into the Atlantic. The Comté and its tributaries are typical Guianan blackwater or clearwater streams, running through lowland rainforest over sandy or rocky substrates. These waters are generally soft, acidic, and poorly mineralised, with low conductivity and pH values often below 6, stained amber by dissolved tannins from leaf litter and decaying vegetation.
The species has not been recorded from other drainages, and its range appears to be restricted to French Guiana. Its small adult size suggests it likely inhabits marginal microhabitats — leaf litter banks, root tangles, and shallow stream margins — where it would be sheltered from larger predators. No depth or microhabitat data specific to this species are available in the published literature.
Feeding
No feeding observations specific to Hemigrammus aereus have been published. Based on its size and close relationship to other small Hemigrammus species from Guianan drainages, it is presumed to be a micropredator and opportunistic omnivore. Species of this size in similar Neotropical stream habitats typically feed on small invertebrates — zooplankton, micro-crustaceans, insect larvae, and small aquatic insects — as well as algae and fine organic matter.
In the aquarium, if the species were to become available, it would likely accept fine-grade prepared foods and small live or frozen invertebrates such as baby brine shrimp, Daphnia, and micro-worms, consistent with the feeding requirements of comparably sized tetras from the Guiana Shield.
Mating
No documented observations of reproductive behaviour in Hemigrammus aereus exist in the published or hobby literature. Members of Hemigrammus are typically egg-scattering open spawners: males court females with fin displays, and spawning occurs among fine-leaved vegetation or over the substrate, with adhesive or semi-adhesive eggs scattered and left without parental care.
For a species of this size from soft, acidic Guianan waters, spawning would likely be triggered by replication of natural conditions — warm, very soft and slightly acidic water, subdued lighting, and fine-leaved plants or synthetic spawning mops as a substrate for egg deposition. These conditions parallel those used successfully for closely related small tetras from the same region.
Breeding
No captive breeding records for Hemigrammus aereus have been located. The species is not known to be maintained in the aquarium hobby. Based on analogies with related Hemigrammus from Guianan drainages, breeding would follow the egg-scattering pattern typical of the genus: adhesive eggs deposited among fine vegetation, hatching within 24 to 48 hours under warm conditions, with the tiny fry requiring infusoria or rotifers as first foods before graduating to larger live and prepared foods.
As with most small tetras from acidic Guianan waters, successful breeding in captivity would likely require soft, acidic water, gentle filtration, and removal of adults after spawning to prevent egg predation. Growth to adult size at roughly 1 in SL would proceed over several months under good conditions.
In the aquarium
Hemigrammus aereus does not appear to be available in the ornamental fish trade, and no aquarium care guides specific to the species have been located. It is documented primarily from museum specimens and taxonomic literature.
Should the species become available, the standard approach for small Guianan tetras would apply: a mature, well-filtered aquarium with soft and slightly acidic water, dim or diffuse lighting, a substrate of fine sand or leaf litter, and planting with fine-leaved species. A small group of six or more would be appropriate, as small tetras are shoaling fish that show more natural behaviour and reduced stress in conspecific company. Its very small adult size — around 1 in SL — would suit a nano or species aquarium, or a community with other small, peaceful fishes from similar water conditions.
Conservation
Hemigrammus aereus has not been formally assessed by the IUCN Red List; its conservation status is Not Evaluated (NE). The absence of an assessment reflects the general pattern for the many hundreds of small, narrowly distributed Neotropical characins whose population status and trends are largely unknown.
The species is known from the Comté River basin of French Guiana, a region that retains extensive lowland rainforest cover and benefits from relatively low human population pressure compared with other parts of South America. French Guiana's protected area network includes a substantial fraction of its territory. While no specific threats to H. aereus have been documented, small-ranged fish species in Guianan drainages may face localised pressures from alluvial gold mining (orpaillage), which degrades stream habitats through sedimentation and mercury contamination. A formal assessment would require targeted surveys to establish the species' actual range and population status.