Taxonomy & naming
Odontostilbe nareuda was described by Lúcia Bührnheim and Luiz Roberto Malabarba in 2006 in a systematic revision of the genus Odontostilbe. The type locality is a lake on the right bank of the río Nareuda, approximately 2 mi above its confluence with the río Tahuamanu in the department of Pando, Bolivia — waters that belong to the lower río Beni basin and ultimately to the upper Amazon via the río Madeira. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) records the valid name as Odontostilbe nareuda Bührnheim & Malabarba, 2006.
Odontostilbe is placed within Characidae in its broad sense. The genus groups a series of small, slender tetras found across tropical South America, and the 2006 revision by Bührnheim and Malabarba significantly reorganised species boundaries within it. O. nareuda is distinguished from close relatives by a combination of meristic characters including anal-fin ray count (24–26), anal-fin base length as a proportion of standard length (30.6–32.8 % SL), and coloration.
Morphology
Odontostilbe nareuda is a slender, laterally compressed tetra of modest size. Males reach 1–1.5 in standard length; females are slightly larger, up to approximately 1.5 in SL. The body form is typical of the genus: elongate and streamlined, with a small mouth, a single dorsal fin, and a forked caudal fin. The anal fin is notably long relative to body length, with 24–26 rays, a character used in the original description to distinguish this species from similar Odontostilbe.
Coloration in life has not been described in detail for this species in available sources. On the basis of close relatives, the general appearance is likely a silvery to translucent body with a faint lateral stripe and a hint of iridescence, without bold markings — a pattern suited to schooling in open or semi-vegetated water. Sexual dimorphism is moderate: females are deeper-bodied and larger; males are more slender.
Habitat
The type locality for O. nareuda is an oxbow lake on the right bank of the río Nareuda in the department of Pando in northern Bolivia. The species is also recorded from the río Muyumanu, a nearby tributary, and the broader distribution likely encompasses suitable lowland habitats within the lower río Beni drainage and possibly the wider río Madeira basin.
The original description characterises the río Nareuda itself as a system receiving both blackwater and whitewater inputs, with a substrate of sand and mud overlain by organic debris. Oxbow lakes in this landscape are characteristically warm, shallow, and seasonally connected to the main river channel. No specific temperature or pH data for the collection localities have been published; the general conditions of Amazonian lowland floodplain lakes in this region suggest warm tropical temperatures and circumneutral to slightly acidic water chemistry, though this remains unconfirmed for this species specifically.
Feeding
FishBase assigns O. nareuda a trophic level of 2.5, consistent with a diet centred on small invertebrates — zooplankton, microcrustaceans, aquatic insect larvae, and similar prey — supplemented opportunistically by plant material or detritus. This is the typical feeding guild of small characids in floodplain and oxbow lake systems, where they occupy the lower trophic rungs as secondary consumers.
No detailed dietary study specific to this species has been published. The inference from trophic level and congener ecology is that it feeds in the water column and near the surface, targeting prey by sight in daylight hours. In an aquarium context, small live and frozen foods such as Artemia nauplii, Daphnia, and fine crushed flake would be appropriate based on size and inferred ecology.
Mating
No direct observations of mating behaviour in Odontostilbe nareuda have been published. By analogy with other small characids of similar ecology, the species is expected to be an egg-scattering open spawner in which males court females without forming lasting pair bonds. Courtship likely involves males pursuing females and displaying with fin erection as is common across Characidae.
In floodplain systems, small characids often spawn in association with rising water levels and the flush of new aquatic vegetation that follows inundation. Whether O. nareuda exhibits strong seasonal spawning tied to the flood pulse of the lower Beni system is unknown.
Breeding
No captive-breeding records for Odontostilbe nareuda are known from the available literature, and the species is not established in the ornamental trade. Based on the biology of the genus and the broader small-characid pattern, breeding can be inferred to follow the egg-scattering mode: adults scatter small adhesive or semi-adhesive eggs among fine-leaved aquatic plants or over substrate, with no parental care and a significant risk of egg predation by the adults themselves.
Incubation period and fry development are undocumented for this species. General small-characid practice — separating spawning adults from eggs, rearing fry in a quiet container, and starting with very fine first foods such as infusoria or commercial micro-fry preparations before graduating to newly hatched brine shrimp — would apply as a baseline if captive breeding were attempted. Breeding maturity is not recorded.
In the aquarium
Odontostilbe nareuda is not a species currently available in the ornamental-fish trade and is unknown in hobby circles. It is essentially a scientifically described species from museum collections and fieldwork rather than an aquarium fish. Any care information must therefore be extrapolated from the genus and from small lowland-Amazon characid ecology more broadly.
Were it to become available, the expected requirements would align with other diminutive tetras from Bolivian and Peruvian lowland drainages: a well-established aquarium with stable warm water in the range typical of tropical floodplains, gentle filtration, and a group of at least six to eight individuals to permit natural schooling behaviour. Fine-leaved plants and subdued lighting would likely suit a species from shaded oxbow lake environments. Given its small adult size, tankmates should be chosen carefully to avoid predation.
Conservation
Odontostilbe nareuda is assessed as Least Concern on the IUCN Red List, with the assessment completed in 2021. The LC status reflects a distribution across the lower río Beni basin and the broader río Madeira watershed — one of the most species-rich river systems in South America — and no currently identified major threats specific to this species.
Nonetheless, the lower Beni and upper Madeira drainages in the Pando region of Bolivia face ongoing pressures from deforestation, agricultural expansion, and, more recently, hydroelectric development in the broader Madeira basin. Floodplain oxbow lakes, the primary habitat recorded for this species, are sensitive to catchment disturbance. The species' actual population size and precise range limits are poorly characterised, and its conservation status has not been subject to detailed reassessment. Collection of wild specimens for scientific study would require permits under Bolivian wildlife regulations.