Taxonomy & naming
Hyphessobrycon hexastichos was described by Luiz Roberto Malabarba Bertaco and Flávio Cesar Teixeira Carvalho in 2005. The holotype (MCP 37648) measures 2 in standard length and was collected in the Chapada dos Parecis region of Mato Grosso state, Brazil, which drains into the upper rio Tapajós, a major right-bank tributary of the Amazon. Eschmeyer's Catalog of Fishes recognises Bertaco & Carvalho, 2005 as the valid authority combination.
The species belongs to Hyphessobrycon, the largest and most species-rich genus of small New World characins in the family Characidae. The genus is defined informally rather than by strong synapomorphies, and its limits have been debated since Lima et al. (2003) overhauled Characidae higher classification. H. hexastichos sits within a broadly mid-Amazon to upper-Amazon assemblage of striped small tetras but has not been formally placed in any named species group. Its relationships within the genus remain incompletely resolved.
Morphology
H. hexastichos is a slender, laterally compressed characin reaching roughly 1.5 in in standard length in aquarium specimens, consistent with the holotype of 2 in SL reported from the original description. The body is elongate and pale, with the most distinctive feature being the series of horizontal dark stripes running the length of the flank — the six lines that give the species its name and underpin the common name Six-line Tetra.
Like most Hyphessobrycon, the species shows a small but distinct humeral spot and faint lateral banding that may intensify under stress or during courtship. The caudal fin often shows a dark mid-lobe stripe. Sexual dimorphism is subtle at rest; females in breeding condition are noticeably fuller-bodied than males, as is typical for the genus. No unusual armature or adipose-fin modifications are noted in the original description.
Habitat
The type locality is in the Chapada dos Parecis, a broad plateau in central-western Mato Grosso that reaches elevations of around 1969–2297 ft and is drained by headwater streams of the rio Tapajós system. Stream habitats on the Chapada tend to be clear, relatively fast-moving, and oxygen-rich, with sandy or rocky substrate and fringing gallery forest providing shade and leaf litter.
Water conditions in upper Tapajós drainages are typically soft and mildly acidic to neutral — characteristic of the central Brazilian shield — though the Chapada dos Parecis catchment shows some local variation. The species has been collected from freshwater environments in Brazil and is not known outside the upper Tapajós basin. Its known range is therefore relatively restricted, centred on the highland headwaters rather than the broader lowland Tapajós.
Feeding
Like virtually all members of Hyphessobrycon, H. hexastichos is an opportunistic omnivore in the wild, taking small invertebrates — insect larvae, microcrustaceans, and zooplankton — together with algae and fine organic matter that drift through its stream habitat. The species forages across the water column, though it tends toward the middle layers in quieter water.
In the aquarium it is undemanding and readily accepts dry foods, including good-quality flake and small pellets. Supplemental feeding with frozen or live Daphnia, brine shrimp, and bloodworm improves condition and encourages spawning behaviour. A varied diet reduces the risk of nutritional deficiencies and keeps the striping contrast at its most vivid.
Mating
Hyphessobrycon hexastichos is an egg-scattering open spawner, consistent with the general Hyphessobrycon reproductive mode. Males display to females with lateral posturing and colour intensification, and spawning takes place among fine-leaved vegetation or spawning mops. The adhesive eggs are scattered and attach loosely to plant surfaces or substrate; no parental bond is formed and adults will consume eggs given the opportunity.
Conditioned pairs or small groups are the typical approach in captivity. Soft, slightly acidic water and a temperature in the mid-to-upper range of the species' tolerance tend to stimulate spawning activity. Males in a group display more actively in the presence of rivals, and a slightly skewed sex ratio with more males than females is often recommended to keep display intensity high.
Breeding
Aquarium Glaser reports H. hexastichos as hardy and easily bred in large numbers in captivity, which aligns with broader hobbyist experience and makes it one of the less demanding small tetras to propagate. A separate breeding tank with fine-leaved plants such as Java moss, or a layer of synthetic spawning mops over a mesh that separates adults from the eggs, is the standard approach. Water temperatures of 75–82 °F and a pH in the slightly acidic to neutral range promote spawning.
The adhesive eggs hatch in approximately 24–36 hours at typical breeding temperatures; the larvae are free-swimming and feeding within a few days. First foods should be infusoria or commercial liquid fry foods, with newly hatched brine shrimp introduced as the fry grow. Growth is reasonably rapid and juveniles develop their characteristic striping within the first few weeks. Removing adults immediately after spawning maximises fry survival.
In the aquarium
H. hexastichos is well-suited to smaller community aquaria. Its 1.5 in adult size, peaceful disposition, and undemanding care requirements place it comfortably in tanks from about 15 US gal upward, and it shows best in a group of six or more individuals, where the striped pattern creates a cohesive shoal effect. A planted tank with open swimming lanes and a dark substrate throws the horizontal lines into relief.
Water conditions noted in hobbyist sources span a wide range — pH 6.0–8.0 and temperatures of 75–82 °F — reflecting the species' tolerance and adaptability in captivity, even if its wild habitat likely runs softer. Tankmates should be similarly sized and peaceful; other small tetras, small rasboras, Corydoras catfish, and dwarf cichlids all make compatible companions. The species is reported to be hardy once established, tolerating the minor fluctuations of a well-maintained community tank without difficulty.
Conservation
Hyphessobrycon hexastichos has not been formally assessed by the IUCN Red List, and its conservation status is therefore Not Evaluated (NE). Its known range is restricted to the upper rio Tapajós basin in Mato Grosso, Brazil, which places it within a region experiencing ongoing agricultural expansion — the Chapada dos Parecis plateau is a centre of large-scale soy and cotton farming — with associated pressures on riparian and headwater stream habitats through deforestation, erosion, and chemical run-off.
No targeted conservation assessments or population surveys for this species appear in the published literature accessible at the time of writing. Its apparent tolerance of aquarium conditions and the ease of captive breeding suggest that it could be maintained sustainably through tank-bred stock, which would reduce any collecting pressure on wild populations. A formal IUCN assessment incorporating range data from the original type locality and subsequent collections would help clarify its status.