Taxonomy & naming
Psalidodon pellegrini was described by Carl H. Eigenmann together with McAtee and Ward in 1907, with the original description appearing at page 136 with accompanying plate illustration. Eschmeyer's Catalog of Fishes (California Academy of Sciences) records the current valid name as Psalidodon pellegrini, with Astyanax pellegrini treated as a junior synonym following the generic revision that transferred many former Astyanax species to the reinstated genus Psalidodon. The species is therefore correctly written with the authority unparenthesised, as the genus assignment has not changed from Psalidodon under the current classification.
The species belongs to the large and taxonomically complex subfamily Stethaprioninae / incertae sedis assemblage that encompasses the former Astyanax sensu lato. Genus Psalidodon was re-erected to accommodate a clade of South American characids whose phylogenetic relationships had been obscured by the century-long aggregation of dozens of species under Astyanax. The name Astyanax pellegrini remains in wide use in the aquarium hobby and older literature, and both names will be encountered in catalogues and biotope documentation.
Morphology
Psalidodon pellegrini is a typical streamlined characid, reaching a maximum recorded standard length of 3.1 in according to FishBase. The body is laterally compressed and moderately elongate, with the silvery flanks characteristic of open-water members of the family. A dark or dusky lateral stripe runs along the midline toward the caudal peduncle, ending in a caudal spot — a pattern shared with many congeners and useful for identification within the broader assemblage.
The fins are hyaline or faintly pigmented, and the species possesses the adipose fin typical of characids. Sexual dimorphism is modest and follows the general Astyanax pattern: females are deeper-bodied when gravid, but the sexes are otherwise difficult to distinguish externally in non-breeding condition. No striking colour polymorphism or local variant is documented in the available sources.
Habitat
The species occupies the Paraguay River basin, with distribution confirmed across Argentina, Brazil, and Paraguay; the FishBase record also notes the Bahia Negra locality in northern Paraguay near the Bolivian border. It is classified as a benthopelagic freshwater fish, inhabiting the lower and mid water column of rivers and associated floodplain features. Biotope documentation places it in slow, deep tributaries of the Lower Paraguay River, in the Ñeembucú wetland region of Paraguay, where it co-occurs with Cichlasoma dimerus and Corydoras species.
The Pantanal and surrounding floodplain lowlands of the Paraguay basin support a mosaic of gallery forest streams, oxbow lakes, and seasonally inundated grassland — habitats that characids exploit during high-water periods and retreat from as waters recede. The species is described as tropical and is presumed to track the seasonal flood pulse common to all Paraguay basin fishes, though detailed ecological studies specific to this species are not available in the accessible literature.
Feeding
Specific dietary data for Psalidodon pellegrini are not resolved in FishBase or the available cache sources, and detailed gut-content studies have not been widely published for this species. By inference from its body shape, habitat, and the well-documented feeding ecology of close relatives within the Psalidodon / Astyanax assemblage, the species is almost certainly an opportunistic omnivore — taking small invertebrates (aquatic insects, crustaceans, worms), plant matter, algae, and allochthonous items falling to the water surface.
In the aquarium, members of this genus are reliably undemanding feeders that accept flake and small pellet foods, frozen bloodworm, Daphnia, and brine shrimp. Offering dietary variety maintains condition and supports reproductive cycling in captive groups.
Mating
Psalidodon pellegrini is a sexually reproducing species, as recorded by Encyclopedia of Life. Like other members of the Astyanax / Psalidodon complex, it is presumed to practise open egg-scattering spawning with no parental care — the reproductive strategy universal across the clade. Males typically become more active and may show intensified behaviour around ripe females, but no elaborate courtship structures or territory defence are documented for this species.
In the wild, spawning is likely triggered by rising water temperatures and the onset of the rainy season, which drives the flood pulse throughout the Paraguay basin. The eggs are small and adhesive, scattered among fine-leaved aquatic plants or submerged root mats where they adhere and develop without attendance by either parent.
Breeding
Breeding details specific to Psalidodon pellegrini are sparse in the accessible literature. Based on the reproductive biology of closely related Psalidodon and Astyanax species, captive spawning can be expected to follow the standard characid pattern: egg-scattering over fine-leaved plants or spawning mops, with small adhesive eggs that hatch within 24–48 hours at tropical temperatures, and free-swimming fry that require very small initial foods (infusoria, rotifers, or commercial fry preparations) before advancing to newly hatched brine shrimp.
Adults will consume both eggs and fry if not separated after spawning. Conditioning adults on live and frozen foods prior to an attempted spawn typically improves egg production and fertilisation rates. The absence of published captive-breeding accounts in the accessible sources suggests the species has not attracted dedicated attention from specialist breeders, though its basic requirements should not differ markedly from the many successfully bred members of the same genus.
In the aquarium
Psalidodon pellegrini is not among the most frequently kept tetras in the hobby, and purpose-collected specimens seldom appear in trade outside of South American specialist suppliers and biotope enthusiasts interested in the Paraguay River system. It is best suited to a Paraguay or Pantanal biotope aquarium recreating slow, deep tributary conditions: tannin-stained or clear warm water, a soft sandy substrate, drifting leaf litter, and areas of rooted or floating vegetation providing cover.
The biotope documentation from Ñeembucú, Paraguay places it alongside Cichlasoma dimerus and Corydoras species — a natural community template for the biotope aquarist. As a schooling characid it should be kept in groups of at least six to express natural behaviour and reduce shyness. Water temperature in the mid-to-upper 20s Celsius, neutral to slightly acidic to neutral pH, and good filtration with low to moderate flow suit its floodplain origins. It is peaceful and compatible with similar-sized community fish from the same drainage.
Conservation
Psalidodon pellegrini is assessed as Least Concern (LC) on the IUCN Red List, with the assessment dated 04 March 2021 as recorded by FishBase. The Least Concern listing reflects the species' occurrence across a broad geographic area spanning three countries (Argentina, Brazil, Paraguay) within the extensive Paraguay River basin — one of South America's largest and most hydrologically intact river systems relative to many Atlantic drainages.
No specific threats to the species are flagged in the available sources. The Paraguay basin faces broader environmental pressures including wetland conversion, agricultural run-off into the Pantanal, and infrastructure development along river corridors, but these have not been assessed as pushing this wide-ranging species toward a threatened category. Continued monitoring of the Paraguay basin's overall ecological health will be the most relevant conservation context for the species in coming decades.