Taxonomy & naming
Astyanax robustus was described by Seth Eugene Meek in 1912, with the original description appearing on page 69 of his work. The type locality is given as the Virginia River, Costa Rica, and the holotype is deposited in the Field Museum of Natural History (FMNH 7682). The Catalog of Fishes (Eschmeyer) records the valid combination as Astyanax robustus Meek, 1912.
The genus Astyanax Baird & Girard, 1854 is one of the largest in the family Characidae, with species distributed from the United States through Central America and across most of South America. The taxonomic history of the genus is complex: molecular studies conducted from the late 2000s onward have steadily reorganised its boundaries, with some species moved into resurrected or newly erected genera. As of the comprehensive 2024 Checklist of Characiformes (Toledo-Piza, Baena, Dagosta, Menezes & Zanata), Astyanax robustus is retained within Astyanax, though the checklist notes that the type locality has not been precisely located.
The epithet robustus is Latin for stout or strong, likely a reference to the body form of the holotype. No standardised common name is in wide use for this species.
Morphology
Detailed morphological data for Astyanax robustus are sparse in the available literature, and no published maximum standard length figure was located in sources examined. As a member of Astyanax, the species would be expected to share the genus's characteristic body plan: a moderately compressed, oval to fusiform silver-bodied characid with a terminal mouth, an adipose fin, and the single dark or dusky caudal spot or lateral stripe that recurs across many members of the group.
Without a published redescription or measurement data, specific meristic counts (scales in lateral line, fin-ray counts) and precise size ranges cannot be reliably stated here. Aquarists who obtain specimens identified as this species should treat size estimates based on congeners as approximate until dedicated study is published.
Habitat
The type locality for Astyanax robustus is the Virginia River, Costa Rica. Distribution records in the freshwater fish checklists for South and Central America indicate the species as present in Costa Rica, though the checklist notes some uncertainty regarding the precision of locality data. FishBase records the species under a tropical freshwater environment in Costa Rica.
Like most Astyanax species in Central America, A. robustus would be expected to inhabit clear to moderately turbid lowland rivers and streams in forested and open landscapes, with warm, near-neutral water. Astyanax species in this region commonly use vegetated margins, overhanging bankside cover, and riffle-pool sequences. Precise water-chemistry records from the Virginia River or its tributaries for this species specifically were not located in available sources.
Feeding
No dedicated dietary study for Astyanax robustus was found in available literature. Astyanax species as a group are generalised omnivores, taking small invertebrates (insect larvae, aquatic crustaceans, surface-fallen insects), plant material, algae, and detritus in proportions that shift with season and habitat productivity. Central American Astyanax in particular have been documented eating fruits, seeds, and leaf material in riparian habitats during periods of flooding when terrestrial material enters the water.
In the aquarium, fish of this genus are typically easy to feed, accepting dried flake and small pellets alongside frozen and live foods such as Daphnia, Artemia, and bloodworm. A varied diet is preferable for maintaining condition.
Mating
No published account of mating behaviour specific to Astyanax robustus was located. The genus Astyanax as a whole reproduces by broadcast egg-scattering with no pair bond and no parental involvement in guarding or tending the spawn. Research on genus-level reproductive biology indicates that most Astyanax species show a seasonal peak in reproductive activity correlated with the onset of the rainy season, when rising water levels, increased food availability, and reduced water temperatures in run-off all act as spawning triggers.
Displaying males of Astyanax species generally pursue gravid females through open water or over substrates, and spawning is often a group activity rather than a strict pair event, with multiple males attending a single female. No elaborate courtship structures or nest-building are known for the genus.
Breeding
Astyanax robustus has not been documented as a bred species in the aquarium literature examined. Based on genus-level biology, breeding would follow the standard Astyanax pattern: egg-scattering over fine-leaved plants, submerged vegetation, or open substrate, with the female releasing adhesive or semi-adhesive eggs that the adults do not guard. Incubation at tropical temperatures is typically brief — hatching within 24–48 hours is common in warm-water Astyanax — and the larvae are initially small and require fine first foods.
For aquarists wishing to attempt breeding, conditioning on varied live and frozen foods, a seasonal temperature drop of a few degrees followed by a return to normal, and the provision of fine-leaved plants or spawning mops would replicate conditions used for other Central American Astyanax. Parents should be removed after spawning to prevent predation on eggs and larvae.
In the aquarium
Astyanax robustus has essentially no dedicated hobbyist profile in English-language sources, and it is not commonly encountered in the trade under this name. Aquarists who obtain specimens — most likely as contaminants in shipments of other Central American livebearers or characids — can treat them as typical small Astyanax: active schooling fish that do best in groups of six or more in a well-filtered, moderately planted aquarium.
Water conditions matching the tropical freshwater of Costa Rica — temperatures in the mid-to-upper 20s Celsius, neutral to slightly alkaline pH, moderate hardness — should suit the species. As schooling fish, they are peaceful with similarly sized tankmates and pose no particular challenge to maintain on standard prepared and frozen foods. Their rarity in the hobby means husbandry notes are necessarily extrapolated from close relatives rather than direct experience.
Conservation
Astyanax robustus has not been assessed by the IUCN Red List. No formal conservation status has been published for this species, and it does not appear in the IUCN database as an evaluated taxon. Its restricted type locality in Costa Rica, combined with uncertainty about its current range and whether it is synonymous with or distinct from other regional Astyanax, makes population assessments difficult without targeted fieldwork.
Costa Rica's freshwater fish fauna is reasonably well studied relative to much of Central America, and the country maintains substantial protected areas covering major river systems. Whether A. robustus populations occur within protected drainages is not known from available sources. The species' taxonomic status would benefit from examination of the holotype and comparison with recently described or revised Central American Astyanax to confirm its validity and establish its actual range.