Taxonomy & naming
Astyanax puka was described by Juan Marcos Mirande, Guillermo Aguilera, and Marta M. de Azpelicueta in 2007 in the journal Zootaxa (volume 1646, pages 31–39). The holotype, CI-FML 3844, measures 2 in standard length and was collected from the Río Salí basin in Tucumán province, Argentina. The species is endemic to that basin, with no verified occurrences outside its native drainage.
The valid name as registered in Eschmeyer's Catalog of Fishes is Astyanax puka Mirande, Aguilera & Azpelicueta, 2007. FishBase and some subsequent aggregators list the species under the synonym Psalidodon puka, reflecting a generic reassignment proposed after the original description; however, the placement of many 'Astyanax' remains contested across the literature and the Catalog of Fishes governs the name used here. The specific epithet puka is a Quechua word meaning red or crimson, likely referencing the reddish fins that characterise fresh specimens.
Within Astyanax, the species is distinguished from the morphologically similar A. powelli by the gradual rather than abrupt decrease in dentary tooth size from anterior to posterior, and by the character of the gill rakers. It sits within the highly diverse South American Astyanax assemblage, whose internal relationships remain an active area of systematic study.
Morphology
Astyanax puka is a small fish reaching a maximum recorded size of approximately 2 in standard length in adults, with paratypes ranging from about 1.5–2.5 in SL. The body is shallow relative to many Astyanax — body depth falling within 33.5 to 39.8 percent of standard length — and the caudal peduncle is proportionally long, at 13.3 to 16.5 percent of SL, contributing to a somewhat slender, streamlined silhouette.
The lateral line is complete, with 36 to 38 perforated scales, and the transverse scale count is 6 above and 5 below the lateral line. The anal fin is notably long, carrying 22 to 27 branched rays, a count that aids in distinguishing the species from sympatric congeners. The dentition is diagnostic: the dentary bears 9 to 10 teeth that decrease in size gradually from front to back, and a single maxillary tooth is present and distinctively expanded distally, bearing 7 to 9 cusps — a character absent or differently expressed in many related species. A narrow humeral spot is present, visible as a small dark mark just behind the opercle. Males develop small bony hooks on the pelvic and anal fins during reproductive maturity, a form of sexual dimorphism shared with many characids.
Habitat
Astyanax puka is restricted to the Río Salí basin in northwestern Argentina, encompassing river systems in the provinces of Tucumán and Catamarca. The Río Salí is part of the larger Río Dulce system, draining the eastern slope of the Andes at the southern end of the sub-Andean zone. The species inhabits freshwater, reportedly with benthopelagic tendencies, in a subtropical climatic zone characterised by marked wet and dry seasonality.
No detailed water-chemistry data specific to Astyanax puka have been published in the available literature. The Río Salí and its tributaries carry water that is influenced by Andean geology, typically moderately hard and close to neutral in the upper, less disturbed reaches. The lower portions of the basin have been heavily modified by agricultural channelization and water diversion; the IUCN notes that the upper portion of the range remains relatively intact but faces increasing anthropogenic pressure. Population density across the basin is not well-documented.
Feeding
No detailed dietary study of Astyanax puka in the wild has been published. As is typical for small riverine Astyanax, the species is presumed to be an opportunistic omnivore exploiting whatever invertebrate and plant material is available in its habitat, including small insects, crustaceans, and plant debris. The benthopelagic habit noted for the species in FishBase suggests it forages across the water column rather than being restricted to a single zone.
In an aquarium setting, Astyanax species of comparable size and ecology generally accept a broad range of prepared foods — flake, small pellets, and frozen or live invertebrates such as Daphnia and bloodworm. A varied diet supports condition and colour. Because the species is rarely encountered in the hobby, species-specific feeding data from captivity are not available.
Mating
Sexual dimorphism in Astyanax puka is subtle but documented: mature males develop bony hooks on the rays of the pelvic and anal fins — a trait observed in many characids and often associated with physical contact during courtship or spawning. No field study of the species' reproductive behaviour has been published, and its mating system is inferred from knowledge of closely related Astyanax.
In riverine Astyanax generally, males show courtship activity in the form of chasing and lateral displays, and spawning is preceded by active pursuit of females through dense vegetation or open water. No pair bond or territory is established; the interaction is transient and competition among males may be intense. Spawning in the wild is likely tied to seasonal flooding or rising water temperatures in the wet season, as is common across South American characids.
Breeding
Astyanax puka has not been documented in the aquarium trade or captive breeding programmes, and no specific breeding account is available. Based on the biology of the genus and the family Characidae broadly, the species is expected to be an egg-scattering, open-water or plant-associated spawner with no parental care. Eggs are typically adhesive or semi-adhesive, scattered among fine-leaved vegetation or deposited over substrate, and both eggs and larvae are left unguarded.
Characid eggs at tropical and subtropical temperatures generally hatch within 24 to 48 hours, with free-swimming larvae appearing a day or two later. First foods for very small characid fry are typically infusoria or rotifers before progression to newly hatched brine shrimp. Growth rates and time to maturity for this species are unrecorded. Any captive breeding would likely require a species tank with fine-leaved plants or spawning mops and separation of adults from eggs after spawning.
In the aquarium
Astyanax puka is essentially unknown in the aquarium hobby and is not commercially available. It has no established common name in English, and its small size — around 2 in SL — would in principle make it suitable for a modestly sized aquarium if it were ever to enter the trade. Its subtropical origin (Tucumán is at roughly 26–27°S) suggests it may tolerate a wider temperature range and cooler conditions than most South American tetras from equatorial lowland rivers.
In a hypothetical aquarium context, the care requirements of similar small Astyanax species would be a reasonable starting point: a well-planted tank with soft to moderately hard water, neutral to slightly alkaline pH, and good filtration. The species is expected to be peaceful and schooling, suitable as part of a community of similarly sized fishes. At present, any specimens would be wild-caught research material, not hobby stock, and the species' Near Threatened status and restricted natural range would make collecting for ornamental purposes inadvisable.
Conservation
Astyanax puka is assessed as Near Threatened (NT) on the IUCN Red List, with the most recent assessment published in 2021. The Near Threatened designation reflects a combination of restricted range — the species is endemic to the Río Salí basin and occurs nowhere else — and documented habitat degradation in the lower portion of that basin. Agricultural channelization and water diversion have substantially modified the lower Salí drainage, reducing habitat quality and potentially fragmenting populations.
The upper portions of the Río Salí basin in the Andean foothills remain relatively intact at the time of the 2021 assessment, and the species has not yet undergone the quantified population decline required for a Vulnerable or Endangered listing. However, its narrow endemism means that any future expansion of agricultural or urban land use in Tucumán and Catamarca provinces could rapidly push it toward more threatened categories. No specific conservation management programme for the species is documented, and its status in captivity remains nil.