Taxonomy & naming
Scopaeocharax rhinodus was described by the American ichthyologist James Erwin Böhlke in 1958, originally under the name Tyttocharax rhinodus. The type locality is a quebrada (stream) at Puente Pérez, approximately a quarter-mile above the río Huallaga at Tingo María, in the department of Huánuco, Peru, at an elevation of roughly 2297 ft. The species was later placed in the genus Scopaeocharax, where Eschmeyer's Catalog of Fishes (the authority for valid names) records it as Scopaeocharax rhinodus (Böhlke, 1958); the parenthetical authority reflects the change of genus.
The genus Scopaeocharax belongs to the family Characidae. Molecular and morphological work has variously placed it within or near the subfamily Stevardiinae — a clade that includes the glandulocaudine group of neotropical characids — though its exact position remains a matter of ongoing revision as the broader characid phylogeny is resolved. Scopaeocharax is a small genus of just two species: S. rhinodus and S. atopodus. The two are distinguished by body proportions and stripe pattern; S. rhinodus is noted for its more elongate form, sharper rostrum, and broader midlateral band.
Morphology
S. rhinodus is a very small fish, with a maximum recorded standard length of 1 in. The body is elongate and laterally compressed, more so than in S. atopodus, tapering to a notably pointed head — the species epithet rhinodus references this, from the Greek for 'snout-toothed' or 'pointed snout'. The overall build is typical of a small, pelagic characid adapted to open-water or mid-column swimming in fast-to-moderate Andean foothill streams.
A broad midlateral stripe runs along the flank, darker and more pronounced than in its congener. The fins are small and hyaline, and the lateral line is complete as is typical for the group. Detailed meristic data (scale counts, fin-ray counts) are recorded in the original description but are not reproduced here; the combination of small size, elongate proportions, pointed head, and prominent lateral band distinguishes the species in the field.
Sexual dimorphism is not well documented for this species. In many small characids females become noticeably deeper-bodied when gravid, which may be the only reliable field distinction.
Habitat
The species occurs in the upper and middle Huallaga River basin of Peru, at elevations in the Andean foothills. The type locality at Tingo María sits at approximately 2297 ft elevation in Huánuco department, in a zone of transition between the high Andes and the western Amazon lowlands. Subsequent collection records extend the species' range to include parts of Ecuador and the Vaupés region of Colombia, suggesting the species uses Andean-foothills drainage across a broader span of western Amazonia.
FishBase categorizes S. rhinodus as a freshwater pelagic species, indicating it tends to occupy open water or mid-column positions rather than bottom-hugging or heavily vegetated microhabitats. In the Andean foothills, streams and small rivers at this elevation are typically well-oxygenated, cool to warm, moderately soft to slightly hard, and subject to seasonal variation in flow. Specific physico-chemical data for the type locality quebrada are not available in the literature reviewed here.
Feeding
FishBase assigns Scopaeocharax rhinodus a trophic level of 3.0, indicating it is broadly in the mid-level carnivore to omnivore range — consuming small invertebrates, microcrustaceans, insect larvae, and possibly fine particulate organic matter. A pelagic lifestyle in foothill streams is consistent with feeding on drifting invertebrates in the water column.
No detailed gut-content studies appear in the published literature reviewed. Like most small characids, it is likely an opportunistic feeder, taking whatever small prey items are available in the water column at its size range. In captivity, small-particle prepared foods, live or frozen Daphnia, cyclops, and brine shrimp nauplii would be appropriate, though the species is not commonly kept in the hobby and practical feeding accounts are sparse.
Mating
No specific mating observations for Scopaeocharax rhinodus have been published. Based on its placement among characids — and within a lineage that includes glandulocaudine species with complex courtship involving caudal glands — it is possible that males possess some form of pheromonal or visual courtship signal, but this has not been confirmed for this genus.
In the broader characid pattern, small open-water species are typically egg-scatterers with no parental care. Spawning is likely triggered by seasonal cues such as changes in temperature, conductivity, or water level associated with the Andean wet and dry seasons in the Huallaga catchment. Males in many small characids engage in chase-and-display courtship, following females into fine-leaved vegetation or open water to release adhesive or semi-adhesive eggs.
Breeding
No captive-breeding accounts for Scopaeocharax rhinodus appear in the literature or hobby press. Given its close relationship to other small characids, the general pattern of egg-scattering among fine-leaved plants or open substrate, with no parental care, is the expected mode. Eggs in such species are typically small and adhesive or semi-adhesive, hatching within a few days at tropical temperatures.
The species is not established in the ornamental fish trade, and detailed protocols for its captive reproduction are unknown. Aquarists working with very small, sensitive Andean characids typically offer well-oxygenated, slightly soft, moderately warm water and condition fish with live foods before attempting spawning. Any fry from such a small species would require appropriately fine first foods — infusoria, rotifers, or commercial fry-grade liquid food — before graduating to newly hatched brine shrimp.
In the aquarium
Scopaeocharax rhinodus is not a species currently found in the mainstream aquarium trade. Its very small adult size (1 in SL), somewhat specialized Andean-foothills origin, and limited availability make it a species primarily of interest to specialist collectors of South American microfishes or rare characids rather than the general hobbyist.
For those who do obtain it, an aquarium mimicking the clear, well-oxygenated, moderately cool foothill-stream environment would be appropriate: gentle to moderate current, fine-leaved plants or open swimming space, subdued to moderate lighting, and a small-particle feeding regimen. It should be kept in groups, as small characids are social and benefit from conspecific company. Water chemistry from Andean foothill drainages tends toward soft to moderately hard and slightly acidic to neutral, though specific parameters for the Huallaga basin at the type-locality elevation are not well characterized.
Conservation
Scopaeocharax rhinodus is assessed as Least Concern (LC) on the IUCN Red List, most recently confirmed in the 2022 assessment period. The relatively wide foothill-drainage distribution across Peru, Ecuador, and the Vaupés region of Colombia underpins this assessment, as the species is not restricted to a single small watershed and there are no documented major threats to its primary habitat across this range.
The broader Huallaga River basin and associated Andean foothills do face pressures from agricultural conversion, coca cultivation, and associated deforestation in parts of Peru, which can affect water quality and stream hydrology. However, these pressures have not been assessed as placing S. rhinodus at elevated extinction risk at the species level. As with many small-bodied, widespread Amazonian characids, the limiting factor on knowledge is the paucity of systematic surveys rather than evidence of actual decline.