Taxonomy & naming
Acrobrycon starnesi was described by Arcila, Vari & Menezes in 2014 in a revision of the Neotropical genus Acrobrycon published in Copeia (2013(4):604–611, published 2014). The holotype, USNM 319277 (2.5 in SL), was collected from the Río Thyumayu, a tributary of the Río Azero, in the department of Chuquisaca, Bolivia. The Catalog of Fishes (Eschmeyer, CAS) records the valid name as Acrobrycon starnesi Arcila, Vari & Menezes, 2014.
The genus Acrobrycon belongs to the family Characidae — the largest family of freshwater fishes in the Neotropics — and encompasses only two species. A. starnesi is distinguished from the type species A. taeniatus by a combination of morphological characters detailed in the original description. The specific epithet starnesi is a patronym; the cache does not record the honoree's identity, and the details are not inferred here.
The Río Azero drains into the Río Parapetí and ultimately feeds the upper Guaporé–Mamoré tributary network of the western Amazon basin. The sub-Andean foothills of Chuquisaca are ichthyologically undersampled, and A. starnesi may prove to have a wider distribution than the single known collection point suggests.
Morphology
FishBase records the maximum size of Acrobrycon starnesi at 3 in standard length (SL), making it a small-to-medium characid. The holotype measured 2.5 in SL. No published photographs or detailed colour descriptions for the live fish are available in the cached sources, and fabricating a colour account is not appropriate here.
As a member of Characidae the species shares the family plan of a compressed, moderately deep body, a single adipose fin behind the dorsal, an anal fin of typical characid length, and small cycloid scales. The diagnostic characters that separate A. starnesi from congeners are those in the meristic and morphometric data of the original Copeia description; these are not reproduced here as secondary sources do not summarise them in detail.
Data on sexual dimorphism are sparse in the available literature; no secondary sexual characters have been described in open sources examined during research.
Habitat
The only confirmed collection locality is the Río Thyumayu, a tributary of the Río Azero in the department of Chuquisaca, Bolivia. This places the species in the sub-Andean piedmont zone of the western Amazon basin, a transition zone between the Andes foothills and the Beni–Mamoré lowlands.
FishBase classifies the species as a tropical freshwater fish. The Río Azero system occupies a zone of seasonal rainfall, with river levels and water chemistry varying considerably between wet and dry seasons. No published habitat notes describing substrate type, vegetation cover, water depth, temperature, or physicochemical parameters specific to the Thyumayu collection site appear in the cached sources.
The Guaporé drainage context is noted in the biogeographic literature on Amazonian fishes, and A. starnesi's occurrence in a western tributary fits the general pattern of sub-Andean endemic characids with restricted distributions tied to individual catchments in this orographically complex region.
Feeding
No diet data for Acrobrycon starnesi appear in the literature captured in the research cache. By analogy with other small Amazonian characids it is likely an omnivore or invertivore in the wild, taking small invertebrates, insect larvae, and organic debris from the water column or benthic zone, but this is inference from family-level patterns rather than observation of this species.
In the aquarium, small characids of comparable size generally accept high-quality micropellets and flake food alongside live and frozen foods such as Daphnia, brine shrimp, and bloodworm. Without published feeding records for A. starnesi specifically, these notes are provisional; keepers working with the species should document their observations.
Mating
No mating behaviour has been described for Acrobrycon starnesi in the available literature. As a member of Characidae the species is expected to be an egg-scattering open spawner without parental care — the modal reproductive strategy across the family — though the absence of specific records means this should be treated as a working hypothesis rather than a confirmed account.
Small sub-Andean characids in similar habitats often show opportunistic spawning tied to seasonal flood pulses that trigger gonadal development and spawning migrations. Whether A. starnesi exhibits such seasonality is unknown.
Breeding
Acrobrycon starnesi has not been recorded in the aquarium trade or bred in captivity in any source reviewed during research. The broader pattern for small Amazonian characids suggests egg-scattering over fine-leaved plants or substrate, adhesive or semi-adhesive eggs, no parental care, and adults that will consume eggs if not removed.
Given the species' restricted range, absence from commercial collection, and single known collection locality, captive specimens are not currently available to hobbyists. Should the species ever enter the trade, standard characid breeding protocols — conditioning with live foods, a slightly acidic and soft spawning tank, abundant fine-leaved vegetation or spawning mops, and removal of adults after spawning — would represent a reasonable starting point. Data sparse.
In the aquarium
Acrobrycon starnesi is not currently an aquarium fish. It is absent from commercial collection and from hobbyist literature, and no husbandry records appear in the sources reviewed. Its small size (3 in SL) would in principle make it manageable in a moderately sized community aquarium suited to small South American characids.
Any keeper who does obtain specimens — whether through scientific collection permits or future trade — should treat it as a potentially sensitive species given the narrow geographic origin and unknown tolerance to captive water conditions. Soft to moderately soft, slightly acidic to neutral water typical of sub-Andean Bolivian streams would be a reasonable starting point, with a diet of varied live, frozen, and high-quality dried foods. Documentation of husbandry observations would be a valuable contribution to the knowledge of this poorly known species.
Conservation
The IUCN Red List assessed Acrobrycon starnesi as Least Concern (LC) in 2025. The assessment reflects the absence of identified major threats sufficient to trigger a threatened category at the time of evaluation, though the species' restricted known range — a single tributary of the Río Azero in Chuquisaca, Bolivia — means that baseline data are thin.
The sub-Andean drainages of Bolivia face increasing pressure from agricultural expansion, deforestation in piedmont zones, and potential impacts from hydrocarbon exploration, all of which affect water quality and flow regimes in small tributaries. The Guaporé basin context, noted in Amazonian biogeography literature, includes endemism-rich ichthyofauna that is incompletely inventoried. Additional surveys in the Río Thyumayu catchment and adjacent streams would be needed to establish whether the known distribution underrepresents the species' actual range and to inform future assessments.