Taxonomy & naming
Astyanax varii was described in 2019 by Angela M. Zanata, Rafael Burger, Giulia Vita, and Priscila Camelier. The type locality is a tributary of the rio de Contas basin in Bahia, Brazil, with the holotype measuring 1.5 in standard length and collected from the rio Coricó. Eschmeyer's Catalog of Fishes is the authority for valid names; the name is cited as Astyanax varii Zanata, Burger, Vita & Camelier, 2019.
The genus Astyanax is one of the largest and most geographically extensive genera of freshwater characids in the Neotropics, ranging from the southwestern United States to central Argentina. Astyanax varii is placed within the Northeastern Mata Atlântica ichthyofauna, an assemblage characterised by high endemism in Atlantic coastal drainages of northeastern Brazil. A regional checklist published in Zootaxa 5475 (Vieira-Guimarães et al., 2024) treats the species as endemic (END) to that ecoregion.
Diagnostic characters separating A. varii from congeners include three horizontal scale series between the lateral line and the origin of the pelvic fin, a distal margin of the third infraorbital that is distinctly separated from the preopercle, 34–37 pored lateral-line scales, a conspicuous dark humeral blotch, and a wide midlateral stripe.
Morphology
Astyanax varii is a small, laterally compressed characid with a body plan typical of the genus: a moderately deep oval profile, a terminal mouth, and the single adipose fin characteristic of the family Characidae. The holotype was recorded at 1.5 in standard length; precise maximum size data are sparse for this recently described species.
The colour pattern in preserved material includes a conspicuous dark humeral blotch — a round to oval dark mark immediately behind the operculum — and a wide, well-defined dark midlateral stripe running along the flanks toward the caudal peduncle. These two elements together are important in diagnosing the species from similar Astyanax in the region.
Sexual dimorphism is present: mature males bear bony hooks on all fins, a derived feature shared widely across Astyanax and other characids and associated with tactile contact during spawning. Females lack these hooks.
Habitat
Astyanax varii is known from tributaries of the rio de Contas basin in Bahia, northeastern Brazil. The rio de Contas drains the interior highlands of Bahia before flowing southeast to the Atlantic coast. This drainage falls within the Northeastern Mata Atlântica ecoregion, a biodiversity hotspot characterised by high fish endemism and extensive habitat loss.
Specific microhabitat data for A. varii are not yet well documented in the published record. Astyanax species in Atlantic Forest drainages typically inhabit clear to moderately turbid streams and small rivers, often in association with leaf litter, marginal vegetation, and rocky or sandy substrates. The clima of inland Bahia produces distinct wet and dry seasons that influence water levels and fish ecology across the drainage.
The species' restriction to a single river basin places it in a geographically limited range. Atlantic Forest streams in northeastern Brazil have suffered extensive land-clearing for agriculture and pastoralism, making habitat integrity a persistent concern for endemic species in this system.
Feeding
No dedicated dietary study of Astyanax varii has been published. Astyanax species in Atlantic Forest streams are generally opportunistic omnivores, consuming a mix of aquatic and terrestrial invertebrates, algae, plant fragments, and small amounts of organic detritus, with diet composition varying by season, site, and body size.
In an aquarium context, A. varii can be expected to accept a wide range of prepared and live foods — flake, small pellets, and frozen or live invertebrates such as brine shrimp, Daphnia, and bloodworm — consistent with the feeding ecology of the broader genus. A varied diet is advisable.
Mating
Astyanax varii has not been studied in detail for its reproductive behaviour, but male bony fin hooks are a clear indicator of spawning contact similar to that documented in other Astyanax and related characids. In species where this structure has been studied, hooks on the anal and pelvic fins of males interlock with fin rays of the female during spawning, facilitating close body contact as eggs and sperm are released.
Astyanax generally spawn as open-water, egg-scattering species, releasing adhesive or semi-adhesive eggs among fine-leaved plants or over substrate, with no parental bonding or pair formation beyond the spawning act itself.
Breeding
No captive breeding account for Astyanax varii is available in the published or hobby literature. Based on the biology of closely related Astyanax from Atlantic Forest drainages, the species can be expected to follow the standard characid open-spawning pattern: eggs scattered over fine-leaved vegetation or substrate, adhesive or semi-adhesive, with incubation lasting several days at tropical temperatures and no parental care by either sex.
Adults will likely consume eggs if left together after spawning. Breeders working with similar small Astyanax typically separate eggs to a dedicated rearing vessel, provide gentle aeration, and raise fry on infusoria or commercial liquid fry food before transitioning to newly hatched brine shrimp.
In the aquarium
Astyanax varii is a newly described, range-restricted species not currently established in the ornamental fish trade, and specific aquarium data are absent. Aquarists working with the species by accident or through scientific collections would be advised to treat it as a typical small Astyanax: a peaceful to semi-aggressive schooling fish best kept in groups, tolerant of a range of water conditions consistent with its subtropical to tropical Brazilian habitat, and accepting of standard aquarium foods.
Water parameters reflecting its native drainage — warm, slightly soft to moderately hard, circumneutral pH — are a reasonable starting point. Providing cover in the form of plants or driftwood and keeping the fish in a proper school would reduce stress and elicit natural behaviour. Given its restricted range and Atlantic Forest provenance, any specimens encountered outside Brazil should be assumed to be of conservation interest.
Conservation
Astyanax varii is assessed as Least Concern (LC) in the updated checklist of freshwater fishes of the Northeastern Mata Atlântica ecoregion (Vieira-Guimarães et al., 2024), which compiled IUCN category assignments for the regional ichthyofauna. No dedicated IUCN Red List species-level assessment page has been located for this recently described species.
Endemism to the rio de Contas basin in Bahia is the key conservation context. The Northeastern Mata Atlântica is a highly threatened ecoregion: Atlantic Forest cover in Bahia has been reduced to fragments by centuries of clearing for agriculture, cattle, and urban development, and many endemic freshwater fishes in this region face ongoing habitat pressure. A Least Concern designation reflects the current assessment of extinction risk, but the restricted distribution of A. varii warrants monitoring as land-use pressures in the rio de Contas catchment continue.