Taxonomy & naming
Acrobrycon ortii was described by Arcila, Vari, and Menezes in their 2013 revision of the Neotropical genus Acrobrycon, published in Copeia. The type locality is Villamontes on the Río Pilcomayo, within the Río Paraguay basin, at approximately 21°20'S, 63°37'W in Bolivia. The holotype is deposited at the Colección Boliviana de Fauna (CBF 13305). Eschmeyer's Catalog of Fishes records the valid name as Acrobrycon ortii Arcila, Vari & Menezes 2014, placing the species in the family Stevardiidae (subfamily Hemibryconinae), a clade that has been segregated from the broader Characidae sensu lato by some authorities; the top-level family used here follows Characidae in the broad sense consistent with the site's data model.
The genus Acrobrycon is a small Neotropical genus of characiforms with a disjunct Andean-foothill distribution. The 2013 revision distinguished A. ortii from the congener A. ipanquianus by meristic characters including 19–21 anal-fin rays, a body depth of 22.8–37.4% SL, and a caudal peduncle length 160–230% of body depth; it was also diagnosed against A. starnesi by fin-ray counts, lateral-line scale counts, and caudal peduncle proportions. A note in the IUCN assessment (Ochoa, 2019) questions the species' validity and suggests it may prove synonymous with A. tarijae, but the name remains valid pending further work.
The specific epithet honours the ichthyologist Guillermo Ortí, recognising his contributions to the systematics of Characiformes.
Morphology
Acrobrycon ortii is a small, elongate characid reaching a maximum recorded standard length of 2.5 in. Like other members of the genus it is slender relative to many characiforms, with the body depth falling between 22.8 and 37.4% of standard length. The caudal peduncle is proportionally long, measuring 160–230% of its own depth — a character that, together with anal-fin ray counts, anchors the species' diagnosis within the genus.
FishBase records the species as benthopelagic and tropical, consistent with a foothills stream lifestyle in subtropical to warm-temperate lowlands. Detailed external colour descriptions are not captured in the available sources, and data on live colouration should be considered sparse; the species is not widely kept or photographed in hobby contexts.
Habitat
The species is restricted to the vicinity of the Pilcomayo River near Villa Montes, Tarija Department, Bolivia, within the broader Río de la Plata basin. The IUCN assessment characterises its habitat as streams and ponds in the foothills — transitional environments between the Andean piedmont and the Gran Chaco lowlands.
The IUCN calculates an extent of occurrence of approximately 2,470 mi² and an area of occupancy of 2,134 mi², and identifies the population as occupying a single location. Population trend is listed as unknown. These figures reflect a genuinely narrow distribution rather than incomplete survey; the drainage is accessible, and the species is simply not recorded from elsewhere in the basin.
Feeding
FishBase records a trophic level of 3.0 for Acrobrycon ortii, placing it as a primary carnivore or omnivore at the base of the food web, consistent with the feeding habits typical of small foothills characids. The natural diet is not documented in detail in the available sources.
By analogy with allied hemibryconine and stevardiine characids of similar size and habitat, the species likely feeds on small invertebrates — aquatic insect larvae, microcrustaceans, and terrestrial invertebrates falling to the surface — supplemented opportunistically with plant material or detritus. Data on this species specifically should be regarded as sparse.
Mating
No specific observations of mating behaviour in Acrobrycon ortii are documented in the available sources. Small foothills characids in this group are generally assumed to be egg-scattering open spawners with no parental care, broadcasting adhesive eggs among fine-leaved aquatic vegetation or over substrate, consistent with the broad pattern across Characiformes.
Whether the species exhibits any seasonal spawning tied to the Pilcomayo's hydrological cycle — the river has a pronounced wet-season flood pulse — is not recorded. All mating details here are inferred from family-level patterns; species-specific observations should be sought before treating them as established fact.
Breeding
Breeding in the wild is undocumented in the available literature, and Acrobrycon ortii is not known to be maintained or bred in captivity. In the absence of species-specific data, the most that can be said with confidence is that the genus belongs to a clade (Stevardiidae / Hemibryconinae) whose members are egg-scatterers with no parental care, depositing small adhesive eggs among vegetation or over substrate and abandoning them after fertilisation.
The restricted wild range and Near Threatened status mean that captive breeding would have conservation value if the species were ever established in collections, but no programme appears to exist at present.
In the aquarium
Acrobrycon ortii is not established in the aquarium hobby. It has not been commercially exported, and no husbandry accounts appear in hobby sources. Its small size — just over 2.5 in SL — and foothills-stream origin would in principle suit a modestly sized aquarium with clean, well-oxygenated water and some current, but these observations are speculative in the absence of any captive experience.
Aquarists interested in the genus Acrobrycon or the broader stevardiine diversity of the upper Río de la Plata system should note that specimens, if obtainable at all, would likely come from research collections rather than the trade, and that any meaningful husbandry data would be original contribution to the literature.
Conservation
Acrobrycon ortii is assessed as Near Threatened (NT) on the IUCN Red List, with the assessment published in 2023 based on a 28 October 2020 evaluation by Carvajal-Vallejos. The NT listing is supported by criterion B1a: the extent of occurrence is estimated at 2,470 mi² (below the Vulnerable threshold of 20,0 mi²), and the population occupies a single location, making it acutely susceptible to any single threat event.
Identified threats include water pollution from mining activity in the catchment, deforestation of riparian and upland areas, and water abstraction for agriculture — all pressures consistent with the Pilcomayo's status as one of the most industrially stressed rivers in southern South America. The IUCN notes no confirmed presence of the species in any protected area. An additional taxonomic uncertainty complicates planning: Ochoa (2019) has questioned whether A. ortii is valid or synonymous with A. tarijae; if the two names prove to be the same species, the combined taxon's range may be somewhat larger, potentially affecting the threat assessment. Resolution of this question through fresh material and molecular work would benefit both taxonomy and conservation planning.