Taxonomy & naming
Bryconamericus poi was originally described as Hypobrycon poi by Almirón, Casciotta, Azpelicueta & Cione in 2001, in Neotrópica (La Plata) 47: 33–40, based on material from Uruguay basin tributaries in Misiones province, Argentina. The species was subsequently transferred to the genus Bryconamericus within the family Characidae; Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) recognises the valid combination as Bryconamericus poi with the authority placed in parentheses to indicate the generic transfer.
The family placement reflects ongoing flux in characid systematics. The cache notes an assignment to Stevardiidae by some authorities, a family carved from the broader Characidae for a clade of internally fertilising or sperm-storing South American characins. Whether Bryconamericus sits firmly in Characidae sensu stricto or within Stevardiidae depends on the classification followed; the IUCN assessment and FishBase list the species under Characidae, and that placement is used here consistent with the site's family field.
The specific epithet poi derives from the Guaraní word meaning slender or gracile — a fitting name for a fish whose elongate, fusiform build distinguishes it at a glance from deeper-bodied stream characids. The common name in Spanish is Mojarra, a broadly applied vernacular for small characids across southern South America.
Morphology
Bryconamericus poi is a small, fusiform characid reaching a maximum recorded standard length of 2 in in males and unsexed specimens. The body is notably slender — body depth measures 25.0–29.7% of standard length — which is the morphological basis of its Guaraní name. The dorsal fin carries 8 soft rays; the anal fin is longer, with 17–20 soft rays, a count that falls within the typical Bryconamericus range. The pored lateral line runs through 39–41 scales.
The most reliable external character distinguishing the sexes is the presence of small, rounded nuptial tubercles on the rays of the anal, dorsal, caudal, pectoral, and pelvic fins in males. These bony or keratinised projections are a common feature of breeding-condition male characids and likely play a role in tactile stimulation during spawning contact. Beyond this, coloration is not described in detail in the available sources; like most Bryconamericus the fish is presumed to be silver-sided with a lateral stripe and unremarkable cryptic patterning typical of small stream characins.
Habitat
Bryconamericus poi inhabits fast-flowing streams and small rivers with rocky substrates in the Lower Uruguay ecoregion. Its confirmed range spans Misiones province in northeastern Argentina and adjacent Uruguay — a region of subtropical Atlantic Forest drained by tributaries of the Uruguay River. The IUCN assessment reports an area of occupancy of only 50–60 mi² and an extent of occurrence of approximately 97,409 mi², underscoring how patchily the species is distributed across its nominally broad range.
FishBase classifies the ecology as freshwater, benthopelagic, subtropical — consistent with a species that forages near the substrate in fast, well-oxygenated stream environments. Rocky-bottom, fast-current microhabitats are characteristic of the more rheophilic Bryconamericus species, and the IUCN description of the habitat as rocky substrate streams and small rivers with fast currents aligns with this profile. The species is described as rare within this range, and is not known from standing waters.
Feeding
No specific dietary data for Bryconamericus poi has been published, and the IUCN assessment notes explicitly that no information on diet is available. The broader genus Bryconamericus is typically omnivorous, taking small invertebrates, aquatic insect larvae, algae, and organic detritus from the benthos and water column in fast-flowing stream environments — a generalised feeding strategy common to small stream characids of southern South America.
In the absence of species-specific data, aquarists keeping Bryconamericus species successfully report them accepting small live and frozen invertebrates (Daphnia, bloodworm, Artemia nauplii), fine granules, and crushed flake. Given its benthic tendencies it likely feeds close to the substrate, picking items from and around rocky surfaces. Any aquarium feeding programme should be treated as provisional in the absence of published stomach-content studies.
Mating
No information on the reproductive biology of Bryconamericus poi has been recorded in the literature; the IUCN assessment states this gap explicitly. Based on its genus and the general biology of small South American characids, the species is presumed to be a seasonal egg-scatterer, with males using their nuptial tubercles during spawning contact with females in fast-water habitats.
The presence of well-developed nuptial tubercles across multiple fin types in males is consistent with species in which close physical contact occurs during spawning — tubercles may aid in positioning or stimulating the female during egg release. Spawning in fast-current species is often triggered by seasonal hydrological changes (rising water levels, temperature shifts associated with rainy-season onset), but no field or aquarium observations have been documented for this species specifically.
Breeding
Breeding has not been documented for Bryconamericus poi in either field or aquarium settings; all reproductive data listed in the IUCN assessment is absent. By analogy with congeners and the broader Bryconamericus clade, spawning is expected to follow the egg-scattering mode typical of small non-caring characids: adhesive or semi-adhesive eggs deposited among gravel, cobble, or fine-leaved aquatic vegetation in fast-flowing water, with no parental care after fertilisation.
Aquarists attempting to breed similar small Bryconamericus species typically use well-oxygenated, cooler water with moderate current, a substrate of fine gravel or spawning mops, and trigger spawning with a partial water change that mimics seasonal rainfall. Fry of small characids at this size range require fine first foods (infusoria, rotifers, commercial liquid fry food) before graduating to newly hatched brine shrimp. Until species-specific observations are made, all breeding guidance for B. poi remains extrapolation.
In the aquarium
Bryconamericus poi is not established in the ornamental fish trade and is rarely, if ever, kept in aquaria outside of research contexts. It is a small, subtly marked stream fish without the vivid colours that drive hobby demand, and its restricted range and Near Threatened status make collection for the trade an additional pressure the wild population can ill afford.
For the rare aquarist working with the species, the habitat profile points toward a well-oxygenated, moderately cool aquarium (subtropical temperatures, likely 64–75 °F based on the Misiones climate), with strong flow, a rocky substrate, and good water quality. A shoaling species kept in a group of six or more would show more natural behaviour. Its small size (to 2 in SL) makes it compatible with other small, peaceful stream fish, and its benthopelagic ecology suggests it will spend much of its time in the lower and mid water column. Given the absence of published aquarium data, this profile is necessarily provisional.
Conservation
Bryconamericus poi is assessed as Near Threatened (NT) on the IUCN Red List, published in 2023 from an assessment dated 18 February 2021, under criteria B2b(iii). The listing reflects both the very small area of occupancy (50–60 mi²) and continuing decline in the quality of its stream habitats across Misiones and Uruguay.
Documented threats include eutrophication, agricultural pesticide and herbicide runoff, hydrological alteration of stream flows, and hydroelectric infrastructure that blocks fish dispersal between populations. Population trend is unknown and the species is described as rare; the combination of restricted occupancy and active habitat deterioration places it close to qualifying as Vulnerable. The Atlantic Forest streams of Misiones are among the most threatened freshwater environments in South America, having lost the majority of their native forest cover to plantation agriculture and urban expansion over the past century. Conservation of this species is inseparable from the broader challenge of protecting remnant stream-forest connections in the Lower Uruguay basin.