Taxonomy & naming
Astyanax brevirhinus was described by Carl H. Eigenmann in 1908. The species is placed within Astyanax, one of the most species-rich genera in the family Characidae, with well over 100 valid species spanning a broad swathe of Central and South America. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) is the authority for the valid name Astyanax brevirhinus Eigenmann, 1908; since the species was described in the genus where it remains, no parenthetical authority is used.
The specific epithet brevirhinus is formed from the Latin brevis (short) and rhinus (snout), in reference to the comparatively abbreviated snout that characterises this species among its congeners. The genus name Astyanax derives from Greek mythology — the son of Hector and Andromache — and was applied to this large genus of New World characins by Baird & Girard in 1854.
Morphology
Astyanax brevirhinus is a small, laterally compressed characin reaching up to 4 in total length. Like other members of the genus it has the typical characid body plan: a moderately deep, silvery body, a forked tail, and a small adipose fin between the dorsal and caudal fins that is a hallmark of the family.
The shortened snout noted by Eigenmann is the most readily distinguishing character relative to closely related Astyanax species. Coloration in life follows the genus's common pattern: a bright silver base with a dark lateral stripe running from the mid-body toward the caudal peduncle, often terminating in a dark blotch at the caudal base. Detailed meristic and morphometric data beyond maximum size are sparse in the available literature for this species.
Habitat
Astyanax brevirhinus is endemic to the Jequitinhonha River basin in northeastern Brazil. The Jequitinhonha is one of the major rivers draining the eastern face of the Espinhaço Range into the Atlantic, flowing through a region that transitions between Cerrado and Caatinga vegetation types and is subject to pronounced seasonal variation in rainfall and river discharge.
FishBase records a pH tolerance of 6.2–7.5 for the species, consistent with the slightly acidic to neutral waters typical of many Brazilian coastal river systems. Temperature data from the basin suggest warm, seasonally variable conditions in the range expected for tropical northeastern Brazil. Like most Astyanax, the species is likely to inhabit a range of microhabitats — shallow marginal areas, vegetated banks, and open midwater zones in streams and rivers — though specific habitat data for this species are limited.
Feeding
Astyanax brevirhinus is an omnivore, as is typical of the genus. Wild Astyanax generally feed opportunistically on small invertebrates, insect larvae and adults falling to the water surface, algae, plant matter, and fine organic detritus, with the proportions varying by season and habitat. The short snout of A. brevirhinus may influence how it forages relative to longer-snouted congeners, though detailed dietary studies for this species specifically are not documented in the available literature.
In the aquarium the species readily accepts commercial flake and small granule foods, and benefits from the addition of live or frozen invertebrates such as Daphnia, bloodworm, and brine shrimp to the diet. Some vegetable matter, including blanched leafy greens or spirulina-based foods, is a useful supplement given the omnivorous habit of the genus.
Mating
Like other Astyanax, A. brevirhinus is an egg-scattering, open-water spawner that practices no parental care. Sexual dimorphism within the genus is generally subtle; ripe females tend to be noticeably deeper-bodied and more rotund than males of the same length, which is the most reliable visual indicator of sex in a conditioned group.
Spawning in the wild is likely seasonal, triggered by the onset of the rainy season when rising water levels, temperature shifts, and increased food availability cue breeding activity across many characin species in Brazilian river systems. Males chase females energetically during spawning, and eggs are scattered freely into the water column or among fine aquatic vegetation.
Breeding
Breeding Astyanax brevirhinus follows the pattern shared across the genus: the pair or group scatter small, semi-adhesive eggs among fine-leaved plants or over open substrate, after which the adults show no further interest and will readily consume the eggs and any hatched fry if left together.
Successful breeding in captivity requires separating spawning adults from the eggs promptly, or using a breeding trap or dense spawning mops to protect the eggs. At warm tropical temperatures the eggs hatch within 24–48 hours, producing tiny fry that initially hang near the surface absorbing their yolk sacs before becoming free-swimming and accepting very fine first foods such as infusoria or commercial liquid fry preparations. Newly hatched brine shrimp can be introduced once the fry have grown enough to handle them. Raising fry is straightforward with clean water and frequent small feedings.
In the aquarium
Astyanax brevirhinus is a peaceful, active schooling fish best kept in groups of six or more. A school in an appropriately sized aquarium — a tank of at least 31.5 in in length is advisable for a proper group — will use the full water column and display natural shoaling behaviour. The species does well in a planted aquarium with open swimming space, neutral to mildly acidic water (pH 6.2–7.5), and temperatures typical of its native range in warm tropical Brazil.
It is compatible with other peaceful South American fish of comparable size, including other small characins, corydoras catfish, and dwarf cichlids. Avoid keeping it with fin-nipping species or very small fish that could be outcompeted at feeding. As an adaptable, hardy characin it is tolerant of a reasonable range of water conditions and is not demanding in maintenance, making it suitable for aquarists with some experience of South American community tanks.
Commercial availability of A. brevirhinus is limited compared to more widely traded Astyanax species; it surfaces occasionally through specialist importers and hobbyist networks focusing on Brazilian regional fishes.
Conservation
Astyanax brevirhinus has not been formally assessed for the IUCN Red List; its conservation status is Not Evaluated. The Jequitinhonha River basin, where the species is endemic, faces significant anthropogenic pressures including water extraction for irrigation in a semi-arid region, agricultural runoff, dam construction, and degradation of riparian vegetation — threats that affect many fish species restricted to this drainage.
The narrow endemic range of A. brevirhinus means that basin-level disturbances have outsized consequences for the species. While its adaptability as an Astyanax likely affords some resilience, the combination of a restricted range and an unassessed conservation status leaves its population trajectory uncertain. A formal IUCN evaluation drawing on surveys of current population status in the Jequitinhonha basin would be valuable.