Taxonomy & naming
Hyphessobrycon peugeoti was described by Luiz Fernando Ingenito, Flávio C. T. Lima, and Paulo Andreas Buckup in 2013 from the middle portions of the Rio Juruena drainage, upper Rio Tapajós basin, Mato Grosso State, Brazil. It is placed in the family Characidae and its valid name is recorded in Eschmeyer's Catalog of Fishes as Hyphessobrycon peugeoti Ingenito, Lima & Buckup, 2013.
Within Hyphessobrycon, the species belongs to a small cluster of red-bodied species characterised by the adult male's elongated, filamentous dorsal fin that reaches toward the caudal-fin base when pressed. This trait is shared with H. heliacus and H. loweae but absent in the closely related H. elachys. The combination of vivid overall red colouration in life and the elongated male dorsal fin distinguishes H. peugeoti from most congeners.
Morphology
Hyphessobrycon peugeoti is a small characid reaching approximately 1.5 in standard length, with aquarium literature suggesting up to around 1.5 in total length. The body is slender and laterally compressed, typical of the genus. In life the species is conspicuously red overall, a colouration that intensifies in adult males.
Sexual dimorphism is well developed. Adult males are distinguished by an elongated, filamentous dorsal fin that reaches the caudal peduncle region when laid flat — a striking trait easily seen in mature fish. Males are also larger, develop a more pronounced caudal peduncle blotch, and show richer red on the flanks and fins. The anal fin margin in males is relatively straight, and anal fin rays are thickened. Females are smaller with plainer proportions and a standard unelaborated dorsal fin. Fin hooks, which occur in many Hyphessobrycon, are absent in this species.
Habitat
The species is known from the middle Rio Juruena drainage, upper Rio Tapajós basin, Mato Grosso State, Brazil. Specimens were collected from shallow areas (less than 3 ft depth) at the start of the dry season, from two main microhabitat types: swampy, deforested stream sections with flow choked by grasses and small shrubs, immediately downstream of preserved native forest near the MT-208 highway; and clear, transparent streams with sandy substrates and sparse aquatic vegetation, in flooded areas adjacent to the main Rio Juruena channel.
The type locality is Córrego at Fazenda São Nicolau, left bank of Rio Juruena, Cotriguaçu municipality. The natural environment is soft and acidic: the Aquadiction source records preferred water parameters of pH 5.5–7.5, low to moderate hardness (GH 4–12), and temperatures of 73–81 °F (75–82 °F). The habitat alternates between swampy, seasonally flooded areas and faster-flowing sandy-bottomed streams, suggesting the species is adapted to a range of low-land stream conditions in the Cerrado–Amazonian transition zone.
Feeding
Hyphessobrycon peugeoti is an omnivore. No detailed stomach-content studies from wild populations are documented in the available literature, but its ecological guild — small, active mid-water characid in tropical South American streams — is consistent with opportunistic feeding on small invertebrates, microcrustaceans, insect larvae, and organic detritus, supplemented by plant material and algae.
In the aquarium the species accepts a wide range of prepared and live foods. A staple of quality micro pellets or fine-grade flake can be varied with frozen or live foods including Daphnia, brine shrimp nauplii, and bloodworm. Including some algae-based or plant-nutrient-containing food in the diet is recommended. Small, frequent feedings suit this small-bodied species better than large single meals.
Mating
Like virtually all Hyphessobrycon, H. peugeoti is an egg-scattering open spawner that deposits adhesive eggs among fine-leaved aquatic plants or other fine substrates without providing parental care. The elongated, filamentous dorsal fin of mature males almost certainly functions as a visual signal in courtship and male–male competition, analogous to the role of elaborate finnage in other characids.
Males in breeding condition are easily identified by the extended dorsal fin and intensified red colouration. Courtship likely involves fin-spreading displays in which the male's elongated dorsal fin is erected to its full extent. No detailed ethological studies specific to this species have been published, but the pattern is consistent with closely related red-bodied Hyphessobrycon with elaborated male finnage.
Breeding
Hyphessobrycon peugeoti is an egg-scatterer with no parental care, and the adults will consume eggs if left with them. In the aquarium, breeding follows the general Hyphessobrycon pattern: conditioned adults spawn over fine-leaved plants, Java moss, or spawning mops, releasing small, adhesive eggs that cling to the substrate.
For best results, condition a small group with varied live and frozen foods and move adults to a dedicated spawning tank with soft, slightly acidic water (pH 6.0–7.0, temperature around 77–79 °F), peat filtration or a dark substrate to reduce light levels, and a dense spawning medium. After spawning, remove adults to prevent egg predation. Eggs hatch within a few days at tropical temperatures; the tiny fry initially need infusoria or commercial micro-fry foods before advancing to newly hatched brine shrimp and finely powdered flake.
In the aquarium
Hyphessobrycon peugeoti is a small, active tetra suitable for well-maintained community aquaria with soft, slightly acidic to neutral water. It is best kept in groups of six or more — the species' natural habitat likely includes shoaling behaviour, and males display their ornamental dorsal fins most impressively against one another. A planted aquarium with open mid-water swimming space, a dark substrate to bring out the red colouration, and gentle to moderate filtration flow suits the species well.
Target water parameters drawn from its natural range are pH 5.5–7.5, low to moderate hardness, and 73–81 °F. The species can adjust to moderately harder water with acclimatisation, making it more flexible than many soft-water Amazonian tetras. Peaceful tankmates of similar size — other small tetras, dwarf rasboras, small corydoras, and diminutive livebearers — are appropriate. Avoid large or boisterous fish that may damage the males' elongated dorsal fins, which are the species' most distinctive feature.
Conservation
Hyphessobrycon peugeoti is assessed as Least Concern (LC) on the IUCN Red List, with the assessment conducted on 07 November 2018 by the Instituto Chico Mendes de Conservação da Biodiversidade (ICMBio) and published in version 2022-1. The justification for the LC designation is the absence of identified significant threats to the species at the time of assessment, despite a population trend recorded as unknown.
The species is restricted to small tributaries of the middle Rio Juruena in the upper Tapajós basin, a region subject to ongoing agricultural expansion, deforestation, and wetland modification in Mato Grosso State. The IUCN assessment notes no verified continuing decline in habitat extent at the time of evaluation, but flags research needs in population size, distribution trends, and life-history parameters. The species is not known to occur in any protected areas, and no conservation programmes targeting it have been identified. Its type locality at Fazenda São Nicolau was the site of a reforestation project associated with the Peugeot family, and the surrounding matrix continues to face land-use pressure characteristic of the Cerrado–Amazon frontier.