Taxonomy & naming
Astyanax novae was described by Carl H. Eigenmann in 1911, with the type locality in the Rio Nova drainage of Goiás (then spelled "Goyaz" in the original description), Brazil. Thirteen of the 26 type specimens were collected from the Rio Nova itself. The valid name as recognised by Eschmeyer's Catalog of Fishes is Astyanax novae Eigenmann, 1911; the authority is not parenthetical, as the species was described directly in Astyanax and has not been moved since.
Astyanax is the largest genus in the family Characidae and one of the most broadly distributed vertebrate genera in the Americas, ranging from Texas in the north through Central America and across most of tropical and subtropical South America. The systematics of the genus are notoriously complex: decades of taxonomic work have repeatedly lumped and split species, and molecular phylogenetic studies continue to revise species limits. A. novae belongs to the vast Brazilian interior radiation of the genus, where many species are ecologically similar small, silver-bodied characins that differ primarily in subtle meristic and morphological details.
Morphology
Astyanax novae is a small-bodied characin reaching a maximum recorded standard length of 1.5 in. Like most members of the genus it is a laterally compressed, fusiform fish with the classic characin body plan: a moderately deep body, a forked tail, a single dorsal fin, and the adipose fin that is a hallmark of the broader characid lineage. The general coloration is silvery, typical of open-water Astyanax.
Distinguishing A. novae from its congeners requires examination of meristic characters — scale counts, fin ray counts, and the number and arrangement of teeth on the premaxilla and dentary. These characters are best assessed from preserved voucher specimens; in life, the species is not readily separable from other small Astyanax in the Tocantins system by appearance alone. Data on live coloration and any distinctive markings are sparse in the available literature.
Habitat
Astyanax novae is native to the Rio Tocantins basin in central Brazil, one of the major river systems draining the Brazilian Cerrado and transitional zones toward Amazonia. The type specimens were collected from the Rio Nova in Goiás state. FishBase classifies the species as benthopelagic and strictly freshwater, consistent with the ecology of the great majority of Astyanax species.
The Rio Tocantins system spans a wide range of habitat types, from clear headwater streams in the Cerrado to larger, turbid lowland channels. Water chemistry across the basin varies considerably; studies of the region report warm tropical temperatures typical of central Brazil (broadly 72–82 °F in riverine habitats), with pH and hardness varying by sub-catchment and season. As a small, open-water characin, A. novae likely uses the mid-water column of clear to moderately turbid streams, seeking vegetated margins and shallow areas for cover and foraging.
Feeding
No species-specific feeding studies for Astyanax novae have been published in the accessible literature. By analogy with other small Astyanax, the diet is probably opportunistically omnivorous: small invertebrates (insect larvae, microcrustaceans, terrestrial insects fallen to the surface), algae, and fine organic matter make up the diets of ecologically similar congeners studied across South America.
In an aquarium context, Astyanax species of this size class generally accept a wide range of small prepared foods — micro-pellets, finely crushed flake — as well as small live and frozen foods such as Daphnia and baby brine shrimp. The species is not a specialist and unlikely to present feeding difficulties for experienced keepers of small South American characins.
Mating
No direct observations of courtship behaviour in Astyanax novae have been recorded in the published literature. Across the genus, mating is typical of small characins: males pursue and display to females in the water column, with no territorial defence of nest sites and no lasting pair bond. Spawning is often triggered by environmental cues — a drop in water temperature, a rise in oxygen, or increased rainfall — conditions that in captivity are mimicked by gradual temperature manipulation and water changes.
Research on Astyanax breeding biology broadly indicates that conditioning females on a fat-rich diet for 10–14 days prior to spawning and gradually raising temperature into the upper range of the species' tolerance (toward 79–82 °F) reliably induces spawning activity in receptive fish. Males typically show active pursuit behaviour and may drive females vigorously in the lead-up to egg release.
Breeding
Astyanax novae, like the genus generally, is presumed to be an egg-scattering open spawner with no parental care. Eggs are released into the water column or scattered among fine-leaved aquatic vegetation and submerged plant matter; the adhesive eggs attach by fine threads to plant surfaces. Adults readily eat their own eggs, and breeders of Astyanax species routinely remove adults immediately after spawning or harvest eggs and spawning substrate to a separate rearing vessel.
Incubation times and fry development data specific to A. novae are not available in the literature surveyed. For the genus in general, eggs hatch within 24–48 hours at tropical temperatures, and the tiny fry become free-swimming within a few days of hatching. First foods are typically infusoria or commercial liquid fry foods, progressing to freshly hatched brine shrimp nauplii as the fry grow. Given the small adult size (1.5 in SL), fry are correspondingly small and require fine-particle feeding for the first weeks of life.
In the aquarium
Astyanax novae is not an established aquarium fish and is essentially absent from the hobby literature and commercial trade. It may occasionally appear in shipments of mixed Astyanax from the Tocantins region, but would be virtually indistinguishable from other small congeners without meristic examination. Keepers interested in the Tocantins fauna are more likely to encounter this species incidentally than to seek it out.
Were it to be kept deliberately, the care requirements would follow those of small Astyanax generally: a well-filtered aquarium with gentle to moderate flow, warm temperatures in the 72–82 °F range, neutral to slightly acidic pH reflecting soft-water Cerrado streams, and a peaceful community of similarly sized South American fish. A planted tank with open swimming space and subdued lighting would suit the species. Given its small adult size, tankmates should be chosen carefully to avoid predation; other small tetras and peaceful dwarf cichlids would be appropriate companions.
Conservation
Astyanax novae is listed as Least Concern (LC) by the IUCN, reflecting its occurrence across the Rio Tocantins basin — one of Brazil's large river systems — and the absence of evidence for a rapid population decline. The Tocantins basin has experienced significant anthropogenic pressure, most notably from large hydroelectric impoundments including the Tucuruí Dam, which created one of the world's largest artificial reservoirs and has altered fish assemblages across the lower and middle basin. However, many small Astyanax are resilient generalists capable of persisting in disturbed and modified habitats, which likely contributes to the Least Concern assessment.
The species has no particular profile in conservation or in the ornamental trade, and no captive-bred population of conservation significance is known. The primary conservation concern for the Tocantins basin more broadly is continued dam construction, agricultural runoff, and deforestation of riparian buffers — pressures that affect the entire fish assemblage rather than any single species specifically.