Taxonomy & naming
Astyanax rupestris was formally described in 2018 by Angela M. Zanata, Rafael Burger, and Priscila Camelier in a paper published in Zootaxa (volume 4438, issue 3) titled 'Two new species of Astyanax Baird & Girard (Characiformes: Characidae) from the upper rio Paraguaçu basin, Chapada Diamantina, Bahia, Brazil.' The type specimen (holotype MZUSP 89567) was collected at the rio Coisa Boa, a tributary of the rio Piabas in the Rio Paraguaçu basin, near Igatu, Andaraí, Bahia State. Eschmeyer's Catalog of Fishes registers the valid name as Astyanax rupestris Zanata, Burger & Camelier, 2018.
The species is placed within the Astyanax scabripinnis complex, a diverse assemblage of small, deep-bodied characids associated with upland and montane streams across Brazil. Within this complex, A. rupestris is diagnosed by a combination of characters: the ventral margin of the third infraorbital bone is distinctly separated from the horizontal limb of the preopercle; a midlateral body stripe is absent; a caudal-peduncle blotch is absent; and a vertically elongated, conspicuous dark humeral blotch is present and not bordered by unpigmented areas. The genus Astyanax, placed in the family Characidae, is among the most species-rich vertebrate genera in the Neotropical region.
Morphology
Astyanax rupestris is a small, moderately deep-bodied tetra reaching a recorded maximum of 3.5 in standard length. Like other members of the scabripinnis complex, the greatest body depth falls roughly at a vertical through the midlength of the pectoral fin, giving the fish a characteristic anterior-heavy profile. The branched anal-fin ray count is low for the genus, in the range of 15–21, a shared trait across the complex.
The most distinctive external marking is the humeral blotch — a vertically elongated, solidly dark patch on the flank just behind the gill cover, which is not surrounded by paler, unpigmented tissue. The absence of a continuous midlateral stripe and the absence of a dark blotch at the base of the caudal peduncle further set the species apart from several close relatives within the scabripinnis group. Coloration is otherwise typical of the complex: a silvery body with the usual complement of Astyanax fin and scale pigmentation.
Habitat
The species is endemic to the upper rio Paraguaçu drainage within the Chapada Diamantina region of Bahia, Brazil, one of the most biologically distinctive highland plateaus in the Brazilian interior. The type locality is a rocky-bottomed tributary stream at approximately 1312 ft elevation, and the specific epithet rupestris directly names the stony substrate that characterises this microhabitat. The Chapada Diamantina supports numerous narrow-range endemic fishes in its steep, clear highland streams.
Water conditions in montane Chapada Diamantina streams are typically cool relative to lowland Brazilian rivers, with low conductivity and water that is soft and near-neutral to slightly acidic. The rio Paraguaçu basin drains eastward toward the Atlantic coast of Bahia; the upper basin reaches are isolated from adjacent drainages by highland divides, which explains the high degree of fish endemism in this region. FishBase classifies A. rupestris as freshwater and benthopelagic, consistent with a rocky bottom-associated lifestyle.
Feeding
Astyanax rupestris has a recorded trophic level of 2.9 on the FishBase scale, placing it toward the lower end of omnivory — consistent with a diet combining small invertebrates, insect larvae, and plant or algal material. This is the typical foraging guild for Astyanax species in upland Brazilian streams, where allochthonous input (terrestrial insects falling into streams) supplements aquatic invertebrates and periphyton.
No specific dietary study has been published for A. rupestris. By analogy with well-studied congeners from similar montane stream habitats, the species likely feeds opportunistically on whatever small invertebrates and organic material are available in the drift and on rocky surfaces. In an aquarium context, Astyanax species of this size accept a wide variety of prepared and live foods without difficulty.
Mating
No direct observations of mating behaviour in Astyanax rupestris have been published. The reproductive biology of the broader Astyanax scabripinnis complex, which has been studied in several Brazilian highland populations, involves seasonal spawning linked to water temperature and flow regime in upland streams. Males of characids in this group typically show no elaborate courtship structures, and competition for spawning access is generally diffuse rather than territory-based.
As with other Astyanax, spawning is inferred to be an egg-scattering event in open or vegetated water, with no pair bond maintained beyond the act of spawning itself. FishBase assigns A. rupestris high resilience (minimum population doubling time under 15 months), suggesting a relatively high reproductive rate consistent with open spawning and multiple clutches per season — a typical pattern for small characids in productive stream environments.
Breeding
Astyanax rupestris has not been bred in captivity under documented conditions, and no aquarium breeding account has been published. By reference to the general biology of the scabripinnis complex and to well-studied Astyanax species kept by hobbyists, the reproductive mode is almost certainly egg-scattering with no parental care: males and females scatter adhesive or semi-adhesive eggs among fine-leaved plants or over rocky substrate, then abandon them.
For aquarists who might attempt breeding, the protocols used for upland Brazilian Astyanax generally apply: slightly cooler, soft, lightly acidic water; a well-conditioned pair or small group; and removal of adults after spawning to prevent egg predation. Incubation in comparable Astyanax species at tropical temperatures is typically 24–36 hours, with fry free-swimming within a few days. First foods would be infusoria or commercial liquid fry food, followed by newly hatched brine shrimp.
In the aquarium
Astyanax rupestris is not an established aquarium fish and is essentially unknown in the ornamental trade. It was described only in 2018 from scientific collections in a remote highland area of Bahia, and no commercial collection or export of the species has been reported. As an undescribed narrow endemic from a protected highland region, it is unlikely to enter the hobby in significant numbers.
For specialists who might obtain specimens through research or exchange, the species' natural environment suggests cool, clear, well-oxygenated water with a stony substrate and moderate current. Its small size and likely peaceful disposition would make it compatible with similarly sized, non-aggressive species in a biotope-style setup representing the Chapada Diamantina stream fauna. Low fishing vulnerability (per FishBase) and a restricted natural range argue for caution around any pressure on wild populations.
Conservation
Astyanax rupestris has not been assessed by the IUCN Red List; FishBase records its status as Not Evaluated (NE) as of the 2025-2 global checklist. The species is a narrow Brazilian endemic known only from the upper rio Paraguaçu basin in the Chapada Diamantina, Bahia — a range that by definition qualifies it for scrutiny under IUCN criteria related to restricted extent of occurrence.
The Chapada Diamantina is partly protected as a national park (Parque Nacional da Chapada Diamantina), which provides some habitat security for the type locality. Threats common to upland Brazilian endemics include land clearance for agriculture, water extraction, and changes to stream flow in the semi-arid surrounding landscape. Because the species has been known to science for fewer than a decade and is restricted to a single small drainage, a formal assessment of its conservation status would be a worthwhile priority for Brazilian ichthyological conservation agencies.