Taxonomy & naming
Psalidodon erythropterus was described by the Argentine naturalist Eduardo Ladislao Holmberg in 1891 based on a juvenile specimen from the La Plata River drainage. For over a century the species remained poorly known; it was formally redescribed with both adult and juvenile material by Soneira and colleagues in 2010, which established the modern morphological characterisation of the taxon.
Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) records the valid name as Psalidodon erythropterus (Holmberg, 1891); the parenthetical authority reflects the species' original placement in a genus other than Astyanax. Subsequent generic-level revisions have placed portions of Astyanax in the segregate genus Psalidodon, and FishBase currently treats this species under Psalidodon erythropterus — however, the name remains in flux and Astyanax is used here in its broad, traditional sense pending broader nomenclatural consensus. Astyanax belongs to the tribe Stevardiini within the family Characidae, the largest family of freshwater fishes in the Neotropics.
This fish was long listed as Astyanax erythropterus; Eschmeyer's Catalog of Fishes places the species in Psalidodon, and the current combination Psalidodon erythropterus is followed here.
Morphology
Psalidodon erythropterus is a moderately sized characid with the typically compressed, oval body profile of the genus. The species name — from the Greek erythros (red) and pteron (fin or wing) — refers to reddish colouration in the fins, which appears to be the most immediately visible external character distinguishing it from superficially similar congeners in the La Plata basin.
Beyond this diagnostic feature, the species shares the general Astyanax body plan: a silvery to silver-green flank with a dark midlateral stripe that intensifies toward the caudal peduncle, a dark spot at the caudal fin base, and a short, stout snout housing the genus's characteristic one to two rows of multicuspidate teeth. Precise meristic data (fin-ray and scale counts) were established in the 2010 redescription; for comparative details, Soneira et al. (2010) remain the primary reference.
Habitat
The species is known from the La Plata River basin in Argentina — one of the largest river systems in South America, draining a broad subtropical lowland that spans parts of Argentina, Uruguay, Paraguay, and Brazil. Within that system, Psalidodon erythropterus occupies freshwater environments typical of open-country Argentine rivers and their tributaries: slow to moderately flowing lowland streams, backwaters, and marginal areas with abundant aquatic and emergent vegetation.
Water conditions in the La Plata lowlands are generally warm and range from slightly soft and acidic in headwater tributaries to harder, more turbid water in the main channels. Most Argentine lowland Astyanax inhabit temperatures roughly between 18 and 82 °F across seasons, with the basin experiencing a pronounced seasonal temperature cycle; precise data for this species in the literature are limited.
Feeding
Like essentially all members of Astyanax, P. erythropterus is an opportunistic omnivore. In lowland South American streams, species of this genus consume a wide array of food items including small invertebrates, insect larvae, terrestrial insects that fall to the surface, plant material, algae, detritus, and small fishes. The relative contribution of each category varies with season, habitat, and local availability.
In the aquarium, members of this group adapt readily to commercial foods including flake, micro-pellets, and granules, and accept frozen and live items such as Daphnia, brine shrimp, and bloodworm. A varied diet is beneficial; a diet with some live or frozen component supports conditioning and maintains vigour in active characids.
Mating
Specific courtship data for Psalidodon erythropterus are not documented in the available literature. Based on reproductive biology well established across the genus Astyanax, the species is expected to be an open, non-guarding egg-scatterer. Males in breeding condition typically engage in vigorous pursuit of females, and spawning occurs in the water column or among fine-leaved vegetation with no pair bond formation.
As with most Astyanax, spawning is likely stimulated by seasonal cues — rising temperature in spring and early summer in the La Plata basin, combined with changes in water level and light regime. Neither sex is known to show territorial behaviour or mate-guarding in this genus.
Breeding
Psalidodon erythropterus is, like its congeners, presumed to be a broadcast egg-scatterer that deposits non-adhesive or weakly adhesive eggs freely into the water column or over fine-leaved plants and substrate, with no parental care of any kind. Adults will consume eggs and fry if given the opportunity, which is the norm across the genus.
No specific captive breeding data are recorded for this species in the hobby literature. By analogy with common Astyanax species — including A. fasciatus and A. mexicanus, which breed readily in captivity — conditioning with live or frozen foods and a slight drop followed by a rise in temperature typically triggers spawning. Eggs hatch in roughly 24 to 48 hours at warm temperatures, and fry become free-swimming within a few days, requiring very fine first foods (infusoria, commercial liquid fry food) before graduating to newly hatched brine shrimp.
In the aquarium
Psalidodon erythropterus is not an established aquarium fish and is essentially absent from the ornamental trade; it is known primarily from scientific collections. Aquarists interested in Argentine Astyanax are far more likely to encounter other members of the genus — the widespread banded astyanax or the blind cave form A. mexicanus — than this species.
Should the species become available, its care requirements would mirror those of other mid-sized South American Astyanax: a spacious aquarium with a good swimming lane, neutral to slightly alkaline water in the 68–79 °F range reflecting La Plata basin conditions, and a group of at least six to reduce stress and allow natural schooling behaviour. Planted margins with open swimming space suit the genus well. As an active, shoaling fish it should be kept with similarly sized, non-aggressive tankmates.
Conservation
Psalidodon erythropterus has not been assessed by the IUCN Red List; it carries no formal conservation status. The La Plata basin, while large, faces significant pressures including agricultural runoff, water abstraction, channelisation of waterways, and the spread of invasive species — stresses that affect many endemic freshwater fishes across the Argentine lowlands.
The species' status within the basin is not well documented, and given its limited profile in either scientific surveys or the aquarium trade, it receives little targeted conservation attention. As taxonomic clarity around the Astyanax/Psalidodon complex improves, a more accurate picture of this species' range and abundance may emerge, which would provide the baseline needed for any formal risk assessment.