Taxonomy & naming
Odontostilbe euspilura was originally described by Fowler in 1945. The species sits within the subfamily Cheirodontinae of the family Characidae, a large grouping of small to medium-sized characins distributed broadly across the Neotropics. The genus Odontostilbe contains several species of diminutive, schooling tetras that were historically prone to confusion with one another owing to overlapping meristic characters and similar body plans.
A comprehensive revision of the genus by Bührnheim and Malabarba (2006), published in Neotropical Ichthyology, confirmed O. euspilura as a valid species and clarified its boundaries relative to close congeners such as O. microcephala and O. caquetae. The revision diagnosed O. euspilura partly by its inferior mouth position, which contrasts with the terminal mouth of O. caquetae. Eschmeyer's Catalog of Fishes (Catalog of Fishes, CAS) is the authority for the valid name. The parenthetical authority indicates that the species was originally described in a different genus before being transferred to Odontostilbe.
This fish was long listed as Odontostilbe euspilurus; Eschmeyer's Catalog of Fishes places the species in Odontostilbe, and the current combination Odontostilbe euspilura is followed here.
Morphology
Odontostilbe euspilura is a slender, laterally compressed characin typical of the Cheirodontinae. Maximum recorded size is 1.7 in total length (TL), placing it among the smaller members of a genus already defined by small body size. The inferior mouth position is a key diagnostic character setting it apart from certain congeners with a more terminal mouth.
Like other cheirodontine tetras, the body is generally silvery, deepening slightly toward the dorsal midline, with the lateral line and scale pattern contributing to subtle iridescence in good light. The fins are largely transparent. Reliable colour notes specific to O. euspilura are sparse in the literature, and the species lacks the bold patterning that distinguishes many aquarium tetras. Sexual dimorphism has not been prominently documented in the available sources, though females of small characins are typically deeper-bodied when gravid.
Habitat
The species is endemic to the upper río Caquetá basin in Colombia. The río Caquetá is a major Amazonian tributary rising in the Colombian Andes and flowing southeast into Brazil, where it becomes the río Japurá before joining the Amazon. The upper basin, where O. euspilura is recorded, is a highland-influenced system with warm tropical temperatures and relatively soft, slightly acidic to near-neutral water.
FishBase records the species as freshwater and benthopelagic — living near the bottom but also moving through the water column — under tropical conditions. Reported parameters from FishBase indicate temperatures of 72–79 °F, pH 5.8–7.5, and water hardness up to 20 dH. These figures are consistent with the soft, moderately warm headwater streams and smaller rivers typical of the upper Caquetá drainage. The habitat likely includes areas with substrate cover such as leaf litter and submerged woody debris characteristic of Amazonian headwater systems.
Feeding
Odontostilbe euspilura, like other cheirodontine tetras, is a small-mouthed omnivore adapted to feeding on fine particulate matter in the water column and near the substrate. The subfamily Cheirodontinae is broadly characterized by species that consume microinvertebrates, small crustaceans, zooplankton, algae, and organic detritus depending on availability.
No specific gut-content studies for O. euspilura were found in the available sources, but the benthopelagic habit and small mouth suggest a diet of microcrustaceans, insect larvae, algal filaments, and fine detritus. In the aquarium, species of this size and feeding guild typically accept high-quality micro-pellets, crushed flake, and small live or frozen foods such as micro-worms, Artemia nauplii, and Cyclops, which also help maintain condition.
Mating
Specific reproductive behaviour for Odontostilbe euspilura has not been documented in the accessible literature. By comparison with other cheirodontine tetras and small Characidae generally, the species is expected to be a broadcast egg-scatterer with no parental care — the dominant reproductive mode in the family. Courtship in small characins typically involves brief parallel swimming and chasing behaviour, with males pursuing ripe females into fine-leaved vegetation or over open substrate.
Eggs in egg-scattering characins are generally small, semi-adhesive to non-adhesive, and broadcast into the environment. Adults do not guard the spawning site and will readily consume their own eggs if left together. The spawning of congeners such as O. fugitiva under aquarium conditions suggests that fine-leaved plants or synthetic spawning mops would serve as a suitable substrate for egg deposition.
Breeding
No breeding accounts specific to Odontostilbe euspilura were located in the researched sources, and the species is not currently established in the ornamental fish hobby. Based on the biology of the genus and subfamily, breeding is anticipated to follow the typical cheirodontine pattern: egg-scattering over fine-leaved plants or spawning mops, adhesive or semi-adhesive small eggs, no parental care, and adult removal after spawning to protect the eggs.
Incubation period would depend on water temperature, with warmer water shortening development time. Fry in species of this size are typically very small at hatching and require fine first foods such as infusoria, rotifers, or commercial liquid fry foods before advancing to newly hatched brine shrimp nauplii. Soft, slightly acidic to neutral water matching the species' natural range parameters (72–79 °F, pH 5.8–7.5) would be appropriate for conditioning and spawning attempts.
In the aquarium
Odontostilbe euspilura is not an established aquarium fish and is rarely if ever available in the ornamental trade. It does not appear in standard hobby references, and its appeal lies primarily in the scientific or biotope context rather than as a display animal. Collectors of Colombian Amazonian biotopes or researchers studying cheirodontine diversity might encounter it.
If kept, the species would be best suited to a quiet, well-planted aquarium with soft, slightly acidic to neutral water in the range of 72–79 °F and pH 5.8–7.5, replicating the upper río Caquetá conditions. As a small, schooling characin it should be kept in groups of six or more. Tankmates should be similarly small and non-aggressive. The benthopelagic habit suggests it would use the lower and middle water column. Its small size (under 1.8 in TL) makes it incompatible with larger, predatory fish.
Conservation
Odontostilbe euspilura is assessed as Least Concern (LC) on the IUCN Red List, with the assessment dated 01 March 2007. The LC designation reflects that no major range-wide threats or significant population declines were identified at the time of assessment. The species is confined to the upper río Caquetá basin in Colombia, a region that encompasses substantial areas of relatively intact Amazonian and Andean-foothill forest.
The upper Caquetá has historically been affected by land-use change, agricultural expansion, and the broader pressures facing Colombian Amazonia, including deforestation and water-quality degradation. However, no specific threat data for O. euspilura were recorded in the 2007 assessment. Because the assessment is nearly two decades old, the current population status may differ from what was evaluated; a reassessment with updated distributional and ecological data would better reflect present conditions. The species is not commercially significant in the aquarium trade.