Taxonomy & naming
The species was described by M. de las M. Azpelicueta and M.L. Garcia in 2000, with the type locality recorded as Benítez stream within the Yabotí basin, Misiones province, Argentina. The original combination placed it in Astyanax, the sprawling and notoriously paraphyletic genus that has long served as a catchall for small South American characins.
In 2020, Terán, Benitez, and Mirande published a major phylogenetic revision — 'Opening the Trojan house: phylogeny of Astyanax, two genera and resurrection of Psalidodon' in the Zoological Journal of the Linnean Society — that reorganised the group by resurrecting the genus Psalidodon. Under that revision, the species was reclassified as Psalidodon ojiara. FishBase and some ichthyological databases now carry the species under Psalidodon; however, Eschmeyer's Catalog of Fishes, which this site treats as the authority for valid names, lists the valid combination as Psalidodon ojiara (Azpelicueta & Garcia, 2000). The site retains the original Astyanax combination in the slug and common-usage context while the nomenclature continues to be evaluated in the literature.
Morphology
Astyanax ojiara is a small, slender-bodied characin reaching a maximum recorded standard length of 2 in. Like most members of the Astyanax complex it carries the typical characid body plan: a laterally compressed, fusiform shape with a complete lateral line, an adipose fin, and a rounded or slightly forked caudal fin.
Detailed meristic and morphometric data for this species are sparse in freely accessible literature. FishBase records a trophic level of 3.0 and classifies the species as benthopelagic, suggesting foraging behaviour at or near the substrate in addition to open-water movement. The species is assigned high resilience and low fishing vulnerability — characteristics common to small, fast-maturing characids in well-connected stream systems.
Habitat
The species is known exclusively from the Yabotí stream basin, an affluent of the upper Uruguay River, in Misiones province, northeastern Argentina. The Yabotí system drains subtropical Atlantic Forest terrain characterised by rocky and sandy substrates, clear water with good transparency (reported at 5–7 ft), and abundant marginal and submerged vegetation.
Stream measurements from the ecoregional literature record current speeds between 0.3 and 7 ft/s and depths of 5–11 ft in representative reaches of the Uruguay River ecoregion. The species occupies both headwater and middle-basin stretches of the Yabotí system. Temperature and pH data for this stream system are not precisely documented in the available cache, but the subtropical latitude and Misiones Atlantic Forest setting are consistent with water temperatures in the 68–82 °F range and neutral to slightly acidic conditions typical of clear-water streams over non-calcareous substrates in the region.
Two localities fall within protected areas — the Yabotí Biosphere Reserve and Esmeralda provincial park — but the type locality on Benítez stream sits outside any formal protection. The IUCN records an extent of occurrence of 2,331 mi², confirming the extreme range restriction.
Feeding
No published diet study specific to Astyanax ojiara was captured in the pre-crawl cache. Its trophic level of 3.0, recorded on FishBase, places it as a low-level omnivore or invertivore, consistent with the feeding ecology documented across the Astyanax complex: small invertebrates, insect larvae, organic detritus, algae, and fallen plant material are typical dietary components for stream-dwelling characids of similar size and habit.
The benthopelagic classification suggests the species forages across the water column and at the stream bed. In aquaria, Astyanax-grade small characids of this size class generally accept fine flake food, micro-pellets, and small live or frozen invertebrates such as Daphnia, Cyclops, and newly hatched brine shrimp.
Mating
No published study on the reproductive behaviour of Astyanax ojiara has been captured in the pre-crawl cache. As a member of the Astyanax/Psalidodon complex — and of the family Characidae broadly — the species almost certainly engages in egg-scattering open-water spawning without parental care, the default reproductive mode across the tribe.
Small characids in subtropical Argentina are typically spring–summer spawners triggered by rising temperatures and increased day length, but species-specific data for A. ojiara are not available. Males and females in condition likely aggregate in stream reaches with fine-leaved aquatic vegetation or marginal plant litter, where adhesive or semi-adhesive eggs are scattered among the substrate. No secondary sexual characters distinguishing male from female are documented in the literature available to this project.
Breeding
Captive breeding of Astyanax ojiara has not been documented in the sources captured during the pre-crawl cache assembly, and the species is not known to be established in the ornamental-fish trade. Aquarists wishing to attempt breeding would follow protocols appropriate to small subtropical Astyanax: a separate breeding tank with fine-leaved plants or synthetic spawning mops, a slight temperature increase to induce spawning, and prompt removal of adults after spawning to prevent egg predation.
Egg development time and fry requirements are not available in the cache. General guidance for the complex: eggs typically hatch within 24–48 hours at subtropical temperatures, and the tiny fry require very fine first foods such as rotifers or commercial liquid fry foods before graduating to newly hatched brine shrimp. Growth to adult size would be expected within a few months under good conditions for a 2 in species.
In the aquarium
Astyanax ojiara is not currently documented in the ornamental-fish trade and is unlikely to be available to hobbyists through commercial channels. Its extremely restricted range, the absence of any captive-breeding programme, and the Near Threatened conservation assessment make wild collection inadvisable and commercially impractical.
For reference purposes: a species of this size (2 in SL) and temperament would be suited to a species-appropriate subtropical aquarium replicating the clear, well-oxygenated stream conditions of Misiones — moderate current, rocky and sandy substrate, fine-leaved plants, and temperatures in the 68–77 °F range. As a small schooling characid it would benefit from being kept in groups. The species' conservation status and narrow endemism mean it has no established place in hobby husbandry at this time.
Conservation
Astyanax ojiara was assessed as Near Threatened (NT) by the IUCN Red List in November 2020, with the assessment published in 2022. The evaluation was conducted by J. Liotta and reviewed by T.J. Lyons, under criterion B1b(iii), reflecting a restricted extent of occurrence — 2,331 mi² — combined with continuing decline in habitat quality.
The principal threats are agricultural intensification, particularly tobacco cultivation within the Yabotí catchment, livestock farming, and the resulting pollution from agrochemicals entering the stream system. Population trend is recorded as unknown. Two of the species' known localities lie within the Yabotí Biosphere Reserve and Esmeralda provincial park, providing a degree of protection, but the type locality on Benítez stream is unprotected and subject to ongoing land-use pressures. The combination of a tiny EOO, a single river sub-basin as the entire range, and declining habitat quality positions this species just below the Vulnerable threshold — any contraction of the protected-area localities or further degradation of the unprotected ones could trigger a category uplisting.