Taxonomy & naming
Astyanax goyacensis was described by Carl H. Eigenmann in 1908, with the original account appearing in a report on new genera and species of fishes from Brazil published through the Indiana Department of Geology and Natural Resources. The type locality is recorded as Goiaz — the colonial spelling of Goiás — in central Brazil, and specimens were subsequently tied to the rio Vermelho, a tributary of the rio Araguaia, in the municipality of Goiás, Goiás State.
The species was redescribed by Garutti and Langeani in 2009 in a study published in Neotropical Ichthyology; they examined the holotype alongside 25 topotypes collected from the rio Vermelho and confirmed the species' placement within the Astyanax bimaculatus species complex, a large assemblage of small-to-medium characids distributed widely across South America. The valid name as recorded by Eschmeyer's Catalog of Fishes (entry ID 53393) is Astyanax goyacensis Eigenmann, 1908, with authorship not parenthesised because the species was described in Astyanax, where it remains. FishBase lists the family as Characidae.
Morphology
Astyanax goyacensis is a small, moderately compressed characid with the typical body plan of the bimaculatus complex: a relatively deep, oval profile, a terminal mouth, and the characteristic adipose fin present in most characiforms. The species is benthopelagic in habit, occupying the water column from mid-water to near the substrate.
FishBase records a trophic level of 2.9 ± 0.4, consistent with an omnivorous feeding strategy. Detailed morphometric data were established by Garutti and Langeani (2009) in their redescription, where counts of fin rays, lateral-line scales, and body proportions were used to distinguish the species from congeners in the bimaculatus group. Specific published size data are sparse; the species is typical of the genus in being a small tetra.
Habitat
The species is endemic to the rio Araguaia drainage of Goiás State, central Brazil. The type locality — the rio Vermelho near the city of Goiás — is a clear-to-slightly-turbid river running through the Cerrado biome, a seasonally dry tropical savanna. The Araguaia basin drains a large interior plateau and carries warm tropical freshwater through varied habitats including open channels, marginal pools, and flooded gallery forest during the wet season.
As a benthopelagic, tropical freshwater species, A. goyacensis inhabits the open water column and is associated with the riverine and lacustrine environments of its basin. The Cerrado is subject to marked wet-dry seasonality, and Astyanax species in this region typically respond to flood pulses with changes in distribution and reproductive timing. The species' restriction to Goiás limits its range to a single river basin, though the Araguaia is a large and well-watered system.
Feeding
Astyanax goyacensis is an omnivore. FishBase records a trophic level of 2.9, placing it at a low-to-mid position in the food web and indicating a diet composed primarily of plant matter, detritus, and small invertebrates, consistent with other members of the bimaculatus species complex. Members of this complex are broadly documented as opportunistic feeders that take algae, seeds, terrestrial and aquatic invertebrates, and small amounts of fish material depending on availability and season.
In the aquarium, Astyanax of this type accept a wide range of prepared foods — quality flake and small pellets — as well as frozen and live items such as brine shrimp, Daphnia, and bloodworm. A varied diet supports good condition. Feeding multiple small meals per day is preferable to a single large meal.
Mating
Like other members of the Astyanax bimaculatus complex, A. goyacensis is presumed to be an egg-scattering open spawner with no parental care. Males in breeding condition typically pursue females, and spawning is triggered by environmental cues associated with the wet season in the Cerrado — rising water levels, increasing temperature, and the availability of flooded marginal vegetation where eggs can be deposited.
No species-specific courtship observations have been published for A. goyacensis; behaviour is inferred from the broader genus and complex. Males likely school alongside females and initiate brief chases leading to the release of eggs among fine-leaved submerged plants or into the open water.
Breeding
Astyanax goyacensis is a presumed egg-scattering spawner, as is characteristic of the bimaculatus complex and the genus Astyanax more broadly. Adhesive or semi-adhesive eggs are scattered among aquatic vegetation or over the substrate, where they receive no parental attention; adults do not guard or tend to the clutch or the fry.
In an aquarium setting, conditioning adults with live and frozen foods and providing fine-leaved plants or spawning mops encourages spawning. Separating eggs or adults after spawning reduces predation on the clutch. Incubation and fry-rearing follow the general Astyanax pattern: eggs hatch within a few days at warm tropical temperatures, and the small fry require fine first foods such as infusoria or commercial liquid fry food before transitioning to newly hatched brine shrimp.
In the aquarium
Astyanax goyacensis is not an established hobby fish and is rarely encountered in the aquarium trade. The broader Astyanax bimaculatus complex is widely kept, but individual species within it are seldom distinguished at the retail level. Should specimens become available, the species' husbandry would follow standard care for small, schooling Astyanax: a well-filtered tank of at least 23.5–31.5 in, kept at tropical temperatures, with open swimming space and some plant cover at the margins.
The species is an active, schooling fish best kept in groups of six or more. It is peaceful toward similarly sized tankmates. Water chemistry tolerances in the genus are generally broad, and species from the Cerrado drainage are acclimatised to warm, moderately soft to neutral water. The omnivorous diet makes feeding simple. Because aquarium records specific to A. goyacensis are sparse, hobbyists should consult general guidance for the bimaculatus group.
Conservation
Astyanax goyacensis is assessed as Least Concern (LC) on the IUCN Red List, with the assessment dated 7 November 2018. The evaluation reflects the species' apparent resilience: FishBase records a high resilience rating with a minimum population doubling time of less than 15 months, and fishing vulnerability is low. These attributes are typical of small, fast-reproducing, omnivorous characids.
The Cerrado biome where the species occurs is one of the most threatened biodiversity hotspots in South America, subject to extensive agricultural conversion, water abstraction, and altered hydrology. Localised pressures in the rio Araguaia drainage — sedimentation from deforestation, damming, and agricultural runoff — could affect populations over time, although the current assessment treats the species as not threatened. Monitoring of rio Araguaia basin species is part of the broader challenge of tracking the many small-range freshwater fish of Brazil's interior savanna.