Taxonomy & naming
Hyphessobrycon wosiackii was described by Moreira & Lima in 2017 as one of two new Hyphessobrycon species from the Central Amazon basin, Brazil, published in Zootaxa 4318(1): 123–134. The type material includes paratypes catalogued as ZUEC 14199, measuring 1–1.5 in standard length. The type locality is Igarapé Juruti Grande, a small tributary within the lower rio Tapajós drainage, Pará state, Brazil.
The genus Hyphessobrycon is one of the largest and most taxonomically complex in the family Characidae, encompassing several hundred species distributed across lowland South America and Central America. Valid-name authority rests with Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong), which records the combination Hyphessobrycon wosiackii Moreira & Lima, 2017. The species name honours a person or locality; the full etymology has not been independently verified from the available cache data.
Morphology
Hyphessobrycon wosiackii is a small tetra reaching approximately 1.5 in standard length, as recorded by FishBase. Like other members of the genus it is a laterally compressed, slender-to-moderately deep-bodied fish with the characteristic Characidae adipose fin and a forked caudal fin.
Detailed morphological data from the original description, including scale counts, fin ray counts, and colour pattern in life or preservation, were not available in the consulted sources. The species is distinguished from congeners by a combination of characters evaluated in the original description; aquarists and researchers seeking diagnostic characters should consult Moreira & Lima (2017) in Zootaxa 4318(1).
Habitat
The species was collected from Igarapé Juruti Grande in the lower rio Tapajós basin, a region characterised by blackwater forest streams over sandy substrates. Specimens were found amongst accumulated leaf litter and sunken roots — the sheltered, slow-flow microhabitats typical of many small Hyphessobrycon in Amazonian forest streams.
Water chemistry data recorded at type localities of closely related Hyphessobrycon from comparable Amazonian blackwater drainages suggests soft, acidic conditions: the Practical Fishkeeping source notes type-locality measurements including pH 6.15, conductivity 36 µS, and temperature 79 °F for a related habitat type. These figures are indicative rather than directly measured at the H. wosiackii type locality, and should be treated as a general guide to the genus in this region.
The rio Tapajós is a clearwater and blackwater system draining southward into the Amazon at Santarém; its lower tributaries and northern Amazon bank streams offer forest-shaded, leaf-littered habitats with low nutrient and mineral loads, consistent with the known ecology of small Hyphessobrycon.
Feeding
FishBase records the diet of Hyphessobrycon wosiackii as including algae and arthropods, consistent with the opportunistic omnivory typical of small characids in Amazonian streams. In forest-stream habitats, small tetras of this type feed on whatever invertebrate prey falls or drifts through: surface-fallen insects, small aquatic invertebrates, and organic detritus.
In the aquarium, like most small Hyphessobrycon, this species would be expected to accept a wide range of foods including good-quality micro-pellets and flake, live and frozen invertebrates such as Daphnia, micro-worm, and newly hatched brine shrimp, and fine crushed foods. Varied feeding supports good condition and colouration.
Mating
No specific mating behaviour has been described in the published literature available for this species. Based on the biology of the genus Hyphessobrycon, H. wosiackii is expected to follow the egg-scattering reproductive strategy common to the group: males pursue females and spawning occurs among fine-leaved vegetation or over substrate, with adhesive or semi-adhesive eggs deposited among plant material or leaf litter.
In typical Hyphessobrycon fashion, there is no pair-bond formation and no parental care; spawning activity tends to occur in the early morning under good conditions, triggered by light changes and feeding stimuli.
Breeding
Breeding records for Hyphessobrycon wosiackii in captivity are not documented in the available sources, reflecting the species' recent description (2017) and limited presence in the ornamental trade. Based on the genus norm, breeding would involve conditioning adults on live and frozen foods, providing fine-leaved plants or spawning mops, and separating eggs promptly as the adults will consume them.
Eggs in Hyphessobrycon are typically small, slightly adhesive, and hatch within 24–48 hours at warm temperatures; fry are initially tiny and require infusoria or very fine commercial fry foods before graduating to newly hatched brine shrimp. Water should be soft and slightly acidic to promote fertility, in line with the blackwater origin of this species.
In the aquarium
Hyphessobrycon wosiackii is not established in the mainstream ornamental trade and is unlikely to be encountered outside specialist tetra collectors or Brazilian hobbyist networks. Were it to become available, it would suit a species aquarium or a well-planted community of small, peaceful Amazonian fishes.
As a blackwater tetra from soft, acidic forest streams, it would be best maintained in soft, slightly acidic water (pH around 6.0–6.8, low conductivity), warm temperature in the mid-to-upper 20s Celsius, subdued lighting, and a decorated tank with leaf litter, driftwood, and fine-leaved plants. A group of six or more individuals would allow the natural shoaling behaviour of the species to be expressed. Tankmates should be small and peaceful — other small tetras, dwarf corydoras, and small rasboras would be appropriate.
Conservation
Hyphessobrycon wosiackii has not been assessed by the IUCN Red List; its conservation status is Not Evaluated (NE). The species is known from the lower rio Tapajós drainage in Pará state, Brazil — a region that faces ongoing pressure from deforestation, agricultural expansion, and associated changes to water quality in Amazonian tributary streams.
While no specific population data are available, the reliance of small blackwater forest-stream tetras on intact forest cover makes them inherently sensitive to catchment disturbance. The lower Tapajós region has experienced significant land-use change in recent decades, and monitoring of cryptic small-fish diversity in these habitats remains limited. Formal assessment would require targeted fieldwork and population surveys.