Taxonomy & naming
Hyphessobrycon pinnistriatus was formally described by Carvalho, Cabeceira & Carvalho in 2017, with the original description published in the Journal of Fish Biology. The type locality is the Rio Teles Pires, a major southern tributary of the Rio Tapajós in Mato Grosso state, Brazil. Eschmeyer's Catalog of Fishes (Catalog of Fishes) records the valid name as Hyphessobrycon pinnistriatus Carvalho, Cabeceira & Carvalho, 2017.
The species is placed in Hyphessobrycon, one of the largest and most species-rich genera in the family Characidae, currently encompassing well over 150 described species of small, often brightly coloured tetras distributed across tropical and subtropical South America. Hyphessobrycon as currently constituted is likely polyphyletic, and ongoing molecular and morphological work continues to redefine its boundaries; but the name stands for this species as described. The genus belongs within Characidae (order Characiformes), the family that encompasses the majority of tetras.
Morphology
Hyphessobrycon pinnistriatus is a small tetra of typical Hyphessobrycon proportions — a moderately deep, laterally compressed body. The original description does not provide a maximum standard length figure in the sources available, placing it in the size range typical of small Hyphessobrycon congeners.
The key diagnostic feature is an oblique black stripe on the anal fin, originating at the base of the second branched anal-fin ray and extending to the distal end of the third branched ray. This fin stripe is the character encoded in the species epithet. H. pinnistriatus also lacks the conspicuous black midlateral stripe on the body seen in many congeners, and its inner premaxillary teeth bear up to seven cusps — a dental character supporting its distinction from related species. Overall, fins are described as hyaline or with scattered chromatophores, giving the fish a relatively translucent appearance aside from the defining anal-fin stripe.
Habitat
The species is known from the Rio Teles Pires drainage in Mato Grosso, Brazil, within the Tapajós-Juruena freshwater ecoregion — an area recognised for high levels of aquatic endemism within the Amazonian hydrological network. Observations from the type locality and associated collections indicate that H. pinnistriatus favours lentic environments (still or very slow-moving water), though it has also been encountered in small schools of five to twenty individuals and occasionally singly in slightly more varied conditions.
The Tapajós basin transitions through cerrado, transition forest, and Amazon rainforest habitats in Mato Grosso, and the slow-water microhabitats the species occupies are typically warm, with soft substrates and aquatic vegetation providing cover and feeding grounds for small characids. Distribution data point to restricted occurrence within Mato Grosso state, consistent with the broader pattern of fine-scale endemism among small tetra species in the central Brazilian river systems.
Feeding
No dedicated dietary study of Hyphessobrycon pinnistriatus has been published in the available literature. Based on its morphology and habitat, it is expected to feed in the manner typical of small Hyphessobrycon: an opportunistic micro-omnivore taking small aquatic invertebrates, insect larvae, microcrustaceans, and organic detritus from the water column and substrate.
In an aquarium setting, small Hyphessobrycon of this type accept a variety of prepared and live foods — fine-grade flake and micro-pellets, nauplii of brine shrimp, Daphnia, and similarly sized live or frozen invertebrates. A varied diet supports good condition and colour in these small tetras.
Mating
No specific mating behaviour observations for Hyphessobrycon pinnistriatus appear in the available literature. As a member of Hyphessobrycon, it is expected to follow the family pattern of egg-scattering open spawning with no parental care. Males likely court females with displays involving fin erection and body flaring; spawning occurs among fine-leaved aquatic plants or other structure where adhesive eggs can settle.
Field observations note H. pinnistriatus forming small schools of five to twenty individuals, occasionally also solitary — a social organisation consistent with the loose schooling seen in many small characids during non-reproductive periods. Sexual dimorphism details are not well documented for this species in the available sources.
Breeding
No captive-breeding account specific to Hyphessobrycon pinnistriatus is available in the sources consulted. The genus generally breeds as egg-scattering, plant-spawning fish: conditioned adults scatter small adhesive eggs among fine-leaved vegetation or spawning mops, after which adults show no parental care and should be separated from the eggs to prevent predation.
Incubation and fry-rearing parameters have not been published for this species specifically. General Hyphessobrycon protocols — warm, soft, slightly acidic breeding water; Java moss or synthetic mops; removal of adults post-spawn; first foods of infusoria or commercial liquid fry food followed by newly hatched brine shrimp nauplii — would be the reasonable starting point for anyone attempting captive propagation.
In the aquarium
Hyphessobrycon pinnistriatus is not established in the ornamental trade and is unlikely to be encountered outside specialist research or rare import collections. Its small size and schooling disposition suggest it would suit a planted nano or small community aquarium in the style used for other small Amazonian tetras — soft, warm, slightly acidic water, subdued lighting, dark substrate, and fine-leaved vegetation or floating cover.
Given that it is known from lentic habitats in the Tapajós basin, water chemistry mimicking soft, low-conductivity Amazonian conditions (temperature approximately 75–82 °F, pH 6.0–7.0) would be appropriate. As with all Hyphessobrycon, it should be kept in a school of at least six individuals. Care data remain sparse given the species' obscurity in the hobby, and husbandry would be based primarily on the requirements of closely related congeners.
Conservation
Hyphessobrycon pinnistriatus has not been assessed by the IUCN Red List; no formal conservation status has been assigned. The species appears to be restricted to the Tapajós-Juruena ecoregion, an area of high aquatic endemism, which raises the possibility that its range is naturally limited.
The Rio Teles Pires drainage faces ongoing pressure from hydroelectric development — the Teles Pires Dam complex on the river affects flow regimes and fish passage in the basin — as well as agricultural expansion across Mato Grosso. The impacts of these pressures on small, potentially range-restricted characids such as H. pinnistriatus are not well documented. Formal assessment of its distribution, population size, and vulnerability to habitat change would be needed to evaluate its conservation status.