Taxonomy & naming
Astyanax lineatus was originally described as Tetragonopterus lineatus by Alberto Perugia in 1891, with a type locality of Cáceres (then known as Villa María) on the Río Paraguay in Mato Grosso, Brazil. Eschmeyer's Catalog of Fishes (California Academy of Sciences) records the valid name as Astyanax lineatus (Perugia, 1891), with the authority in parentheses because the species was moved out of its original genus. The specific epithet lineatus — from the Latin for 'lined' or 'striped' — alludes to the lateral banding that characterises the live fish.
Astyanax is one of the largest and most species-rich genera in Characidae, and its limits remain the subject of ongoing ichthyological debate. Several regional revisions have been proposed over the years, and the classification of lineatus relative to allied taxa within the La Plata drainage is not fully resolved. For the purposes of this atlas, the placement follows Eschmeyer's Catalog of Fishes as the authoritative register of valid names.
Morphology
Astyanax lineatus is a slender, silvery characid reaching approximately 4.5 in standard length, as recorded for male and unsexed specimens on FishBase. The body is laterally compressed in the typical Astyanax fashion, moderately deep behind the head and tapering toward a well-forked caudal fin. A dark lateral stripe runs along the midline, referencing the species name, and may intensify under stress or in dim light. The overall coloration is silver with pale ventral surfaces; scattered scales may show a faint iridescent glint under direct light.
The species possesses the small adipose fin present in most characids and bears the family's characteristic small, toothed premaxillary teeth visible at close range. Sexual dimorphism is subtle; as in many Astyanax, females tend toward a rounder, deeper belly profile when gravid, but the sexes are not strikingly different in colour or fin shape outside the breeding season.
Habitat
The species ranges across the La Plata River basin, with confirmed records from Argentina, Bolivia, Brazil, and Paraguay. Within that broad drainage it is associated with smaller river systems, including clear, fast-flowing watercourses of the type documented in Mato Grosso do Sul, Brazil — rivers such as the Rio Sucuri and Rio Formoso where the current is brisk, the substrate sandy, and submerged macrophytes such as Stargrass and Watermilfoil form dense beds.
Water conditions in these biotopes tend toward neutral to mildly alkaline pH, with values around 7.3–7.5 reported and temperatures near 75 °F in the monitored sites. Dissolved oxygen is high due to the current, and water clarity is typically good. The species is benthopelagic in habit, foraging both at the bottom and in mid-water and at the surface depending on food availability, and it relies on vegetated cover for refuge.
Feeding
Astyanax lineatus is a broad omnivore, and a published diet-composition study by Resende et al. (2022) conducted on populations in streams of Mato Grosso do Sul documented a diverse prey spectrum: Chironomidae (midge) larvae, terrestrial insects from multiple orders (Coleoptera, Diptera, Ephemeroptera, Hymenoptera, Orthoptera), detritus and plant remains, filamentous algae, mollusks (Biomphalaria sp.), and even small fish including Poecilia reticulata. The study also found that the species' condition factor reflected the degree of anthropogenic degradation in the streams it inhabits, with less-disturbed sites yielding better-conditioned fish — a detail that illustrates both the species' sensitivity to habitat quality and its dietary opportunism.
In the aquarium the fish accepts a wide range of prepared foods — flake, small pellets, granules — supplemented with live or frozen invertebrates such as Daphnia, bloodworm, and brine shrimp. The natural tendency to feed at multiple levels means it will take food from the surface, mid-column, and substrate with equal readiness.
Mating
Like most small characids, Astyanax lineatus is an open-water egg-scatterer with no parental care. In the wild it is presumed to spawn seasonally in response to rainfall and rising water levels — a common trigger across the La Plata basin — though the specific reproductive phenology of lineatus has not been studied in detail. Males may briefly pursue females in loose spawning chases, but extended courtship displays are not documented for the genus.
In captivity, conditioning a group of adults with high-protein live and frozen foods raises the likelihood of spontaneous spawning. Fish in peak condition will broadcast adhesive or semi-adhesive eggs among fine-leaved plants or over a spawning mop; the adhesive quality varies among Astyanax species, and eggs may settle to the substrate or cling briefly to vegetation. No pair bonding occurs, and both sexes scatter eggs without establishing territories.
Breeding
Breeding Astyanax lineatus follows the general egg-scattering template of the genus. A dedicated spawning tank with a mesh or grating floor (to prevent adults from consuming sinking eggs), or a deep layer of fine-leaved plants such as Java moss, provides egg protection. Water should be soft to moderately hard, slightly acidic to neutral, and warm — temperatures in the range of 75–81 °F promote spawning activity. After conditioning on live foods, the fish can be allowed to spawn as a small group and removed once spawning is observed.
Eggs hatch within 24–48 hours under typical conditions, and the free-swimming fry become active within a few days of hatching. First foods are infusoria, rotifers, or commercial liquid fry food; newly hatched brine shrimp can be introduced once the fry are large enough to handle them, usually within the first week. Growth proceeds at a moderate rate. The adults will consume eggs and fry on contact, so separation is essential to achieving any yield.
In the aquarium
Astyanax lineatus is a manageable, active schooling fish suited to a medium-sized freshwater community aquarium. It does best in a group of six or more individuals — the schooling behaviour becomes more natural and the fish are visibly more settled and bolder than singletons or pairs. A tank of 31.5 in or longer provides adequate swimming space for a small school and allows the fish to display the characteristic fast, darting movements of a river-adapted species.
Water parameters should reflect the neutral, moderately oxygenated conditions of its La Plata River home: pH 7.0–7.8, temperature 72–79 °F, and moderate filtration with some surface agitation. A biotope approach — sandy substrate, dense planting of fine-leaved and broadleaf vegetation, subdued or dappled lighting — shows the fish well and accommodates its natural foraging behaviour. Peaceful community tankmates of similar size and temperament are ideal; avoid slow, long-finned species that may be harassed. The species is undemanding in terms of diet, hardy once established, and readily available where La Plata biotope fish are stocked.
Conservation
Astyanax lineatus has no dedicated formal assessment on the IUCN Red List; FishBase records its status as Least Concern (LC) by inference from its broad distribution and apparent tolerance of a range of conditions across the La Plata basin. That wide range across four countries — Argentina, Bolivia, Brazil, and Paraguay — provides a degree of natural buffering against localised habitat change.
Nevertheless, the research by Resende et al. (2022) illustrates that populations in degraded, heavily anthropogenically modified streams show reduced body condition compared with those in less-disturbed habitats. The La Plata basin faces persistent pressures from agriculture-driven sedimentation, water extraction, channelisation of smaller watercourses, and introduced species, all of which affect the clear, well-vegetated stream habitats that lineatus favours. A formal IUCN assessment for this species would help clarify whether the wide range translates to genuine abundance or whether it masks localised declines in key parts of the range.