Taxonomy & naming
Astyanax marionae was described by Carl H. Eigenmann in 1911 in the Annals of the Carnegie Museum (vol. 8, no. 1). The type locality, as recorded in Eschmeyer's Catalog of Fishes, is six miles from San Luiz de Cáceres, in what is now Mato Grosso state, Brazil, within the Paraguay River drainage. Eigenmann placed the species in Astyanax, then — as now — one of the most species-rich genera of Neotropical characids.
Subsequent molecular and morphological revisions of the Astyanax complex have led some workers to place this species in the resurrected genus Psalidodon, and FishBase carries it under Psalidodon marionae. Eschmeyer's Catalog of Fishes records the valid name as Psalidodon marionae (Eigenmann, 1911), with Astyanax marionae treated as a junior subjective synonym under that arrangement. The parenthetical authority reflects the transfer out of Astyanax. Taxonomic opinion continues to shift in this group, and regional checklists vary; the site indexes the species under its long-familiar combination.
No subspecies are recognised. The epithet marionae is a feminine Latinised patronym, though the exact dedicatee is not established in available sources.
Morphology
Astyanax marionae is a slender, laterally compressed characid reaching approximately 3.5 in standard length (SL) according to FishBase, making it a mid-sized representative of the genus. The body plan is the typical Astyanax blueprint: fusiform, with a blunt snout, a relatively large eye, and the characteristic adipose fin behind the dorsal that marks the family. Dentition includes two rows of multicusped teeth in the premaxilla, as is usual in Astyanax.
Live and preserved colouration has not been described in detail in available sources. Most Astyanax of this size range are silvery-bodied with a dark lateral stripe or caudal spot, but specific markings for A. marionae cannot be confirmed from the cache. The species is benthopelagic in habit, occupying the lower and mid water column in its native waters.
Habitat
The species is native to the Paraguay River basin in central South America. The type locality lies near San Luiz de Cáceres in Mato Grosso, Brazil, and the broader distribution encompasses the Paraguay drainage, a large lowland river system draining the Pantanal wetlands and the surrounding cerrado and transitional zones.
FishBase characterises the species as a freshwater, benthopelagic fish of subtropical waters. The Paraguay basin spans a wide latitudinal range and encompasses slow-moving rivers, flooded grasslands, and lateral lagoons with warm, turbid water during the flood season and clearer, lower water during the dry season. Precise habitat preferences within the basin — whether the species favours main channel, backwaters, or floodplain pools — are not documented in available sources.
Feeding
No detailed dietary study of Astyanax marionae is documented in available sources. Members of the Astyanax complex are broadly opportunistic omnivores, and the genus has been extensively studied in other species as a model for dietary flexibility. Typical wild diets for Astyanax of comparable size include small invertebrates (aquatic insect larvae, microcrustaceans), plant material, and allochthonous matter falling from riparian vegetation.
In the aquarium, Astyanax species of this size are generally undemanding, accepting quality dried foods including flake and small pellets alongside frozen or live foods such as brine shrimp, Daphnia, and bloodworm. A varied diet supports good colour and condition. No specific feeding observations for A. marionae in captivity are available in the current record.
Mating
Specific mating behaviour for Astyanax marionae has not been documented in available sources. The genus as a whole follows the typical characid reproductive strategy of open, broadcast spawning with no parental investment. Males and females school together, and spawning is triggered by environmental cues such as water temperature, photoperiod, and rainfall cycling in the wild.
In the aquarium, Astyanax species generally display brief chasing behaviour by males before spawning, with pairs or groups releasing eggs freely into the water column or scattering them among fine-leaved vegetation. No specific courtship displays or pair bonding have been recorded for this species.
Breeding
No breeding account specific to Astyanax marionae is available in the current record. Based on the biology of closely related Astyanax species, the species is expected to be an egg-scattering open spawner with no parental care. Eggs are non-adhesive or weakly adhesive, scattered among vegetation or onto the substrate, and both eggs and fry are at risk of predation from the adults.
In captive settings, related Astyanax are typically bred by conditioning a group of adults on live and frozen foods, then moving a trio or small group to a separate tank furnished with fine-leaved plants or spawning mops. Eggs hatch within one to two days at subtropical temperatures, and fry become free-swimming shortly after, requiring very small initial foods such as infusoria or commercial liquid fry food before accepting newly hatched brine shrimp. These inferences are based on the genus; species-specific data is sparse.
In the aquarium
Astyanax marionae is not an established aquarium species and is rarely if ever available in the hobby. No husbandry literature specific to this fish has been located. General guidance for similar-sized, subtropical Astyanax applies: a spacious tank with clean, well-oxygenated water, a temperature range suited to subtropical South American conditions, and a school of at least six individuals to reduce stress and produce natural behaviour.
Given its Paraguay basin origins, slightly cooler subtropical temperatures rather than strictly tropical settings may be appropriate, though specific parameters for this species are undocumented. It should not be confused with the cave-adapted blind cavefish (Astyanax mexicanus) or more commonly traded surface-form Astyanax, which differ substantially in ecology and requirements. Data for this species in aquarium contexts is sparse.
Conservation
The IUCN Red List status for Astyanax marionae is recorded by FishBase as Least Concern (LC), though a dedicated IUCN assessment page was not located during research for this article, and the source of that status could not be independently confirmed via the Red List. The species' distribution within the Paraguay River basin is broad relative to many range-restricted Neotropical characids, which may underpin a lower-risk assessment.
The Paraguay basin faces ongoing pressures from agricultural expansion, soy and cattle land conversion in the cerrado, altered hydrological regimes, and periodic industrial contamination. Floodplain species in the Pantanal system are additionally sensitive to water-level manipulation. Without a confirmed IUCN assessment on file, the conservation standing of A. marionae should be treated with caution; data sparse status is a real possibility for a species that generates little hobby or research attention.