Taxonomy & naming
Astyanax elachylepis was described by Vinicius Abilhoa Bertaco and Paulo Henrique Franco Lucinda in 2005, in a paper published in Neotropical Ichthyology. The holotype, MCP 37568 — a male measuring 3.5 in standard length — was collected from ribeirão Arara, a tributary of the rio Maranhão approximately 500 metres from its mouth near Rosariana in the municipality of Niquelândia, Goiás, Brazil (14°02'S, 48°26'W). Paratypes extend the known range into Pará, Tocantins, and Mato Grosso, all within the rio Tocantins basin.
The genus Astyanax Baird & Girard, 1854 is one of the most speciose and taxonomically complex in the family Characidae. Ranging from the southern United States through most of South America, it accommodates well over 100 described species and has been subject to ongoing revision; the exact limits of the genus and which species belong inside it remain an active area of discussion among neotropical ichthyologists. Within that genus, A. elachylepis is placed near species sharing a combination of lateral-line scale counts and caudal-peduncle pigmentation, but its high perforated lateral-line scale count — 48–53, substantially exceeding the 30–45 typical of its nearest relatives — is sufficient to separate it in a straightforward diagnosis.
Morphology
Astyanax elachylepis is a moderately sized characid; the holotype male reached 3.5 in standard length, and museum specimens in the original description range from approximately 1.5–5.5 in SL. It has the typical laterally compressed, fusiform body plan of the genus, with a forked caudal fin and the characid adipose fin present behind the dorsal.
The species is diagnosed by a suite of meristic and pigmentation characters that together distinguish it from congeners: 48–53 perforated lateral-line scales (versus 30–45 in related species); a conspicuous large spot on the caudal peduncle; one or two vertically elongated humeral spots; and a single maxillary tooth. Branched anal-fin ray counts are 22–27. Males bear bony hooks on the dorsal, anal, pelvic, and pectoral fins — a form of sexual dimorphism widespread in characids and thought to function in spawning contact. Females lack these hooks and tend to be more robust-bodied when gravid. Overall colouration is silvery with the humeral and caudal-peduncle spots providing the most visible markings; the species does not display striking colour contrasts.
Habitat
The species is known from the rio Tocantins drainage, one of the great river systems of central and northern Brazil, draining a large portion of the central Brazilian plateau (Planalto Central) into the lower Amazon catchment. The type locality — ribeirão Arara in Goiás — is a small tributary of the rio Maranhão, itself a major headwater tributary of the Tocantins. Additional collecting localities recorded in the original description include sites in Pará, Tocantins state, and Mato Grosso, indicating that A. elachylepis is distributed across much of the upper and middle Tocantins system.
Like most Astyanax species, it probably occupies a range of clear to moderately turbid freshwater habitats including small streams, larger river channels, and associated pools and backwaters. Detailed ecological data specific to this species are sparse in the published record; the water conditions typical of the Tocantins headwater tributaries in Goiás are generally warm and somewhat acidic to circumneutral, reflecting the cerrado (Brazilian savanna) and cerradão landscapes of the basin.
Feeding
No specific dietary studies of Astyanax elachylepis are recorded in the available literature. By analogy with the genus as a whole — which is among the best-studied groups of neotropical characids in terms of feeding ecology — the species is almost certainly an opportunistic omnivore. Astyanax species broadly consume aquatic and terrestrial invertebrates, small fishes, algae, plant matter, and detritus in proportions that shift with habitat, season, and food availability.
In aquaria, fish of this size and genus typically accept prepared foods (flake and small pellets) as well as live and frozen invertebrates such as Daphnia, bloodworm, and brine shrimp. Offering variety supports condition and colouration, though A. elachylepis is not currently a recognised aquarium fish and specific husbandry accounts are lacking.
Mating
Astyanax elachylepis has not been studied in a spawning context in the published record, but the genus is uniformly characterised as open, egg-scattering spawners without parental care. The presence of bony hooks on the fins of males — documented in the original description for dorsal, anal, pelvic, and pectoral fins — is consistent with the hypothesis, widely discussed for hook-bearing characids, that these structures facilitate contact between males and females during spawning, possibly aiding clasping or physical synchronisation of gamete release.
In related Astyanax species, males court females with short chases and lateral displays, and spawning occurs with the pair in close contact, often among vegetation or in open water, with eggs released in small batches rather than a single large clutch. Seasonal cues linked to water level and temperature are likely important in the natural environment, as is common across South American characids tied to the cerrado's wet–dry cycle.
Breeding
No captive breeding accounts for Astyanax elachylepis appear in the hobby or scientific literature; it is not established in the aquarium trade. By genus-level extrapolation, it would be expected to spawn in the manner typical of Astyanax: egg-scattering over fine-leaved plants or open substrate, producing small adhesive or semi-adhesive eggs, with no parental investment and adults that will consume eggs if not separated.
For experimentally minded aquarists working with wild-caught or research specimens, conditions appropriate to cerrado-drainage Astyanax — warm water (75–82 °F), neutral to slightly acidic pH, and fine-leaved plant cover or spawning mops — would represent a reasonable starting point. Incubation in characids of this size typically spans 24–48 hours at breeding temperatures, with free-swimming fry requiring infusoria or equivalent small first foods before advancing to nauplii.
In the aquarium
Astyanax elachylepis is not currently present in the mainstream aquarium trade. No established husbandry accounts, captive-bred populations, or commercial sources are known. The species appears to be collected only incidentally by scientific expeditions within the Tocantins drainage and has not attracted the hobby interest that attaches to more colourful or behaviourally distinctive characids.
Should specimens become available — for example to researchers or specialist breeders — the care requirements would likely mirror those of other mid-sized Astyanax: a roomy aquarium with open swimming space and some planted cover, temperature in the mid-20s Celsius, neutral to slightly soft and acidic water chemistry, a varied omnivore diet, and the company of conspecifics or similar-sized peaceful tankmates. It is not a species an aquarist is likely to encounter through normal retail channels.
Conservation
Astyanax elachylepis has not been formally assessed by the IUCN Red List and carries no conservation category. The rio Tocantins drainage, while large, is subject to significant anthropogenic pressure: construction of the Tucuruí Dam and subsequent hydroelectric development have substantially altered flow regimes and sediment dynamics in portions of the basin, and deforestation of cerrado and riparian vegetation continues to affect tributary water quality and connectivity.
The species' occurrence across multiple states within a large river drainage — Goiás, Tocantins, Pará, and Mato Grosso — suggests it is not narrowly restricted in range, which is a relatively positive indicator compared with endemic species confined to single tributaries. However, without a dedicated IUCN assessment, population trends remain unquantified. As a small characid without commercial fishery or prominent hobby value, it is unlikely to attract targeted monitoring in the near term, and its conservation status depends on the broader health of the Tocantins watershed and the cerrado biome.