Taxonomy & naming
Psalidodon togoi was first described by Adriana Miquelarena and Hugo López in 2006, under the name Hyphessobrycon togoi, based on material from the Chascomús lagoon in Buenos Aires Province, Argentina (type locality approximately 35°45'S, 58°30'W). The original description appeared in the context of the genus Hyphessobrycon in the La Plata basin, and also included discussion of the distribution of that genus within Argentina.
Subsequent taxonomic revision transferred the species to Astyanax, the large and taxonomically complex genus that encompasses a great many small characids across Central and South America. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) is the governing authority for the valid name Psalidodon togoi (Miquelarena & López, 2006); the parenthetical authority reflects the transfer from Hyphessobrycon. No subspecies or synonyms are currently recognised.
The specific epithet togoi is a patronym, though the original paper's dedication details are not reproduced here — the name was assigned by the original authors. The genus Astyanax belongs to the family Characidae, the largest family of freshwater fishes in the Western Hemisphere, and to the subfamily Stethaprioninae in some arrangements, though subfamily-level classification within Characidae remains actively debated.
This fish was long listed as Astyanax togoi; Eschmeyer's Catalog of Fishes places the species in Psalidodon, and the current combination Psalidodon togoi is followed here.
Morphology
Psalidodon togoi is a moderately small characid with a standard length range of approximately 1.75–2.69 in recorded from type series material. The body form is typical for the genus: fusiform, laterally compressed, with a moderately deep profile and the large eye and silvery flanks characteristic of many open-water characids.
The species is distinguished within its assemblage by a well-defined humeral spot — a darkened blotch immediately behind the gill cover — and by a relatively high anal-fin ray count of iv–v 17–20. Mature males bear bony hooks on the rays of all fins, a sexually dimorphic character shared with many Astyanax and formerly Hyphessobrycon species that is used in tactile male-to-male interactions and in spawning contact. Coloration in life is not in detail in the available data, but the genus typically shows a silvery to yellowish lateral stripe, a caudal peduncle blotch, and the humeral spot noted above as the main pigment features.
Habitat
The species is associated with the wet Pampas of Buenos Aires Province — a flat, low-lying region of extensive shallow lagoons, slow rivers, and seasonally inundated grasslands draining into the Río de la Plata system. Type-series material came from Chascomús lagoon, and the species has also been recorded from Laguna de Lobos, Laguna Lacombe, and the Salado River and its tributaries, all of which belong to the Río de la Plata basin.
These environments are both lentic (still or near-still lagoons) and lotic (slow-flowing river channels), and are characterised by abundant floating and submerged aquatic vegetation — totora reed beds, water hyacinth, and fine-leaved macrophytes — that provide cover and invertebrate food resources. The Pampas lagoons are generally shallow, warm in summer, and subject to fluctuating water levels between wet and dry seasons. Specific physico-chemical data for the capture sites are not recorded in the available cache, but the region's lagoons are typically slightly alkaline to neutral and moderately mineralised.
Feeding
Psalidodon togoi is presumed to be an opportunistic omnivore in line with other small Astyanax of similar size and habitat. Its congeners in shallow vegetated Pampas waters typically consume small aquatic invertebrates — insect larvae, microcrustaceans, and small worms — supplemented by plant material and organic detritus available among the macrophyte beds.
No specific dietary studies for this species were located in the research cache, so feeding ecology is inferred from the habitat type and from the well-documented feeding repertoire of closely related Astyanax taxa in the La Plata basin. In an aquarium context, fish of this type accept fine granular and flake foods readily, along with small live and frozen foods such as Daphnia, Artemia nauplii, and chironomid larvae.
Mating
No specific observational data on courtship behaviour in Psalidodon togoi are available. The species can be inferred to be an egg-scattering open spawner based on the presence of bony fin hooks in mature males — a character consistently associated with contact spawning in characids — and on the general biology of Astyanax in vegetated Pampas lagoons.
In related Astyanax species, males compete for access to females in the water column and among vegetation. The bony hooks on male fins are believed to assist in gripping the female during the spawning embrace. Spawning likely occurs in association with fine-leaved aquatic vegetation or submerged plant debris, where adhesive or semi-adhesive eggs can lodge after release. No parental bond or territory defence is expected.
Breeding
Psalidodon togoi has not been documented in the aquarium hobby to any significant degree, and no detailed captive-breeding accounts are available. By analogy with other small Astyanax from similar Pampas-lagoon habitats, it is expected to be an egg-scattering, plant-spawning species that deposits adhesive eggs among fine-leaved vegetation with no parental care; adults would be expected to consume eggs if not removed after spawning.
Typical breeding conditions for Pampas characids involve moderately warm water (around 72–79 °F), neutral to slightly alkaline pH, and the presence of spawning mops or fine-leaved plants such as hornwort or Java moss. Eggs in closely related species hatch in two to three days at typical breeding temperatures, with fry becoming free-swimming shortly after. First foods would be infusoria and very fine powdered foods, followed by newly hatched Artemia as fry grow. These details are extrapolated from the genus rather than directly recorded for this species.
In the aquarium
Psalidodon togoi is effectively absent from the international ornamental fish trade and is not a species that hobbyists are likely to encounter outside of specialist collections or South American fish enthusiasts sourcing locally caught material. Its small size (under 2.8 in standard length) and presumably peaceful, schooling nature make it a candidate for a community aquarium alongside other small South American characids, though no established husbandry literature exists for it.
For aquarists who do obtain specimens, a setup suited to other Pampas-region small tetras would be appropriate: a well-filtered aquarium with abundant planting, open swimming space, neutral to slightly alkaline water at moderate temperatures (68–79 °F reflecting the seasonal Pampas climate), and a varied diet of fine dried foods supplemented with small live or frozen invertebrates. A school of six or more individuals is advisable to express natural behaviour. Given the species' association with vegetation-rich lagoons, some floating plant cover and subdued lighting may help fish settle.
Conservation
Psalidodon togoi has not been assessed by the IUCN Red List and carries a status of Not Evaluated (NE). Its conservation situation is therefore formally unknown, though several aspects of its ecology are worth noting. It is restricted to the lowland lagoon systems of Buenos Aires Province, Argentina — a region subject to ongoing agricultural drainage, water-quality changes from agrochemical runoff, and hydrological modification of the Salado River basin.
The Pampas lagoons that form its core habitat are threatened by eutrophication, periodic drying, and alteration of natural flood-pulse cycles through drainage works. Whether P. togoi is locally abundant within this range or whether its populations are small and fragmented is not established in the available literature. Formal assessment by the IUCN or Argentine national conservation bodies would be necessary to determine whether any protective measures are warranted. At present, the species is known only from a handful of documented localities.