Taxonomy & naming
Hyphessobrycon melazonatus was described by Durbin in 1908, with the type locality recorded as Lagoa do Máximo, Parintins, Amazonas, Brazil. The valid name is governed by Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong), which remains the primary nomenclatural authority for the Characidae.
The species occupies an uncertain position within Hyphessobrycon. According to the IUCN assessment (2018, published 2022), its diagnostic characters are insufficient to distinguish it reliably from congeners, and its taxonomic validity has been questioned. It is considered possibly a senior synonym of Hemigrammus haraldi, a relationship that requires formal taxonomic revision to resolve. The genus Hyphessobrycon is one of the largest and most taxonomically unstable in the Characidae, and species-level boundaries within it have long been contentious. Until a revision addresses H. melazonatus directly, its standing as a valid species remains provisional.
A SciELO paper on new Hyphessobrycon species from the Araguaia basin mentions H. melazonatus in comparative context, noting the ongoing difficulty of distinguishing species within the genus.
Morphology
Hyphessobrycon melazonatus reaches a maximum recorded total length of 1.5 in, placing it among the smaller members of the genus. FishBase assigns a trophic level of 2.9 and characterises the species as benthopelagic, consistent with the typical bottom-to-mid-water foraging behaviour seen in small characids.
Beyond size and general body form, detailed morphological information is sparse in the available literature. The IUCN assessment notes that diagnostic characters are insufficiently distinct from those of congeners, which itself implies that the species conforms to the typical Hyphessobrycon body plan: a small, laterally compressed, silvery to lightly pigmented fish with the usual complement of characid features including an adipose fin and a complete lateral line. No published colour description from living specimens is available in the cached sources, and given that the paralectotype is lost, material for study is extremely limited.
Habitat
The only confirmed locality for Hyphessobrycon melazonatus is Lagoa do Máximo, a permanent freshwater lake near Parintins in Amazonas state, Brazil — a floodplain lake within the Amazon River basin. The IUCN classifies the habitat type as permanent inland wetlands (freshwater lakes), consistent with the broader Amazon floodplain lake system characteristic of the Parintins region.
No detailed habitat parameters such as temperature range, pH, dissolved oxygen, or substrate type have been published specifically for this species or this locality in the cached sources. FishBase notes a tropical, freshwater, benthopelagic lifestyle. Given the species' Amazon basin provenance, warm, seasonally variable floodplain conditions with correspondingly soft, slightly acidic to neutral water are likely, but these parameters cannot be confirmed from available data.
Feeding
Specific dietary data for Hyphessobrycon melazonatus are not documented in the available literature. FishBase records a trophic level of 2.9, which is typical of small omnivorous characids that feed on a mix of small invertebrates, zooplankton, and organic detritus, with limited predation.
By analogy with similarly sized Hyphessobrycon species in comparable Amazonian floodplain habitats, the species likely feeds opportunistically on small aquatic invertebrates, algae, and plant material. In an aquarium context, small-particle prepared foods, live or frozen microfoods such as Daphnia or brine shrimp nauplii, and finely crushed flake would represent appropriate offerings, though the species is not established in the hobby and specific husbandry data are lacking.
Mating
No specific mating or reproductive behaviour has been documented for Hyphessobrycon melazonatus. Based on the general biology of the genus, the species would be expected to follow the egg-scattering pattern characteristic of Hyphessobrycon: open-water or plant-associated spawning in which fertilised eggs settle among fine-leaved vegetation or substrate, with no parental care by either sex.
Males in many Hyphessobrycon species display to females through fin extension and lateral posturing, with courtship occurring in the upper water column or among vegetation. Given the extreme scarcity of specimens and the absence of captive-breeding records, none of these inferences can be confirmed for this species specifically.
Breeding
Hyphessobrycon melazonatus has not been bred in captivity to any documented extent, and no breeding reports appear in the available literature. The species is essentially absent from the ornamental fish trade.
If breeding were attempted, the standard approach for small Hyphessobrycon species would apply: a separate, well-planted breeding tank with soft, slightly acidic water, dim lighting, and fine-leaved plants or synthetic spawning mops to receive adhesive eggs. Adults should be removed after spawning to prevent egg predation. Incubation period and fry requirements are unknown for this species specifically, but newly hatched fry of comparably sized congeners typically require very fine first foods such as infusoria or commercial liquid fry food before advancing to newly hatched brine shrimp.
In the aquarium
Hyphessobrycon melazonatus is not a species encountered in the ornamental fish trade. It is known from a single type locality, has not been collected in recent decades in any documented survey, and remains absent from commercial fish lists. No aquarium husbandry data specific to this species exist.
Were it available, the general care requirements of small Hyphessobrycon would likely apply: a well-planted aquarium, soft to moderately soft acidic water reflecting its Amazonian origin, stable water quality, and a diet of small prepared and live or frozen foods. As with any species of uncertain taxonomic validity, any fish purportedly identified as H. melazonatus would require careful comparison with the published description and, ideally, expert verification.
Conservation
Hyphessobrycon melazonatus is assessed as Data Deficient (DD) on the IUCN Red List, with the most recent assessment completed on 7 November 2018 and published in 2022. The Data Deficient listing reflects not an absence of concern but an absence of information sufficient to make a determination: the species is known only from its lectotype after the paralectotype was lost, no recent confirmed records exist, and its diagnostic characters are considered insufficiently distinct to separate it reliably from congeners. The IUCN notes that taxonomic validity is doubtful pending formal review.
No commercial fisheries use is recorded, and the species is not known to occur within any protected area. It is considered endemic to Brazil (Amazonas state). Given that it has not been collected since the original type series and that the type locality is a floodplain lake in a heavily modified region of the Amazon basin, it is impossible to rule out local extirpation. A taxonomic revision addressing the H. melazonatus — Hemigrammus haraldi question is the most important next step for clarifying both nomenclature and conservation status.