Taxonomy & naming
Ctenobrycon multiradiatus was described by Franz Steindachner in 1876, with the type locality given as the Amazon River at Tefé, in the Brazilian state of Amazonas. It belongs to the genus Ctenobrycon within the family Characidae, the largest family of freshwater fishes in the Neotropics. The genus name derives from the Greek kteis (comb) and bryko (to bite), a reference to the comb-like dentition typical of the group.
The species has a complicated taxonomic history. Géry (1977, 2006) considered C. multiradiatus a junior synonym of Ctenobrycon hauxwellianus, a more broadly documented Amazonian tetra. Lima et al. (2003), in their checklist of freshwater fishes of South America, listed it as species inquirenda — a taxon of uncertain or doubtful identity requiring critical re-examination. The IUCN 2023 assessment follows a provisional stance, treating it as valid while acknowledging that its status may change with future revisionary work. Earlier Argentine and Paraguayan records attributed to this species have since been identified as erroneous, stemming from a misread by Ringuelet et al. (1967); the species is now considered endemic to Brazil.
Morphology
No published description of the external morphology of Ctenobrycon multiradiatus in detail is available beyond the original 1876 account. As a member of Ctenobrycon, it is expected to share the genus's characteristic body plan: moderately deep and laterally compressed, with the large eye, terminal mouth, and adipose fin typical of the Characidae. The common name Lambari, shared across many small Brazilian characids, reflects the general tetra-like gestalt rather than any diagnostic feature of this species in particular.
FishBase assigns a trophic level of 2.7 ± 0.2, derived from the closest relatives rather than observed feeding, which indicates a position low in the food web consistent with invertivory or omnivory typical of small characids. Data on meristics, colouration, and maximum length are not available in the published literature as of the most recent IUCN assessment.
Habitat
The type locality of Ctenobrycon multiradiatus is the Amazon River in the vicinity of Tefé, Amazonas state, Brazil — a broad, sediment-laden river reach in the central Amazon basin. Beyond this geographical point, the IUCN assessment notes that no published information on the species' habitat preferences or ecological requirements exists. It is presumed to occupy freshwater river and wetland environments consistent with the central Amazon floodplain system, which is characterised by warm temperatures, low to neutral pH in blackwater and whitewater zones, and seasonal inundation cycles that shape the availability of food and cover.
The complete absence of ecological records means that claims about specific microhabitat preferences, water chemistry tolerances, or seasonal movements would be speculative. The species has not been collected or documented in the field in any systematic survey since the original type collection.
Feeding
No published records of the diet of Ctenobrycon multiradiatus exist. FishBase assigns a trophic level of 2.7 based on congeners, suggesting a diet of small invertebrates and plant or algal material — the typical feeding guild of small omnivorous characids in Amazonian waters. Members of Ctenobrycon are generally considered opportunistic feeders in the water column, taking invertebrates, detritus, and vegetable matter as available.
In the absence of field data, any more specific account of this species' feeding ecology cannot be given without crossing into inference or fabrication. Aquarium dietary notes are likewise absent from the literature, as the species does not appear to be in cultivation.
Mating
No observations of the reproductive behaviour of Ctenobrycon multiradiatus have been published. By analogy with other small characids in the family Characidae, it is reasonable to expect egg-scattering open spawning without parental care — the predominant reproductive strategy in the family — with adhesive or semi-adhesive eggs deposited among fine-leaved aquatic vegetation or over substrate. Whether any courtship rituals, sexual dichromatism, or other mating-related behaviours distinguish this species from its relatives is unknown.
Given the extreme scarcity of collections and the absence of any aquarium record, the reproductive biology of this species remains entirely undocumented.
Breeding
Ctenobrycon multiradiatus has not been documented in captive breeding programmes and does not appear in hobbyist literature or aquarium trade records. No information on clutch size, incubation period, fry development, or rearing requirements is available. The genus Ctenobrycon as a whole is rarely maintained in the aquarium hobby relative to the more familiar characid genera, and this species in particular appears to have never entered cultivation in any documented way.
If the species were ever to become available for study, the standard Characidae breeding template — fine-leaved plants or spawning mops, slightly acidic to neutral soft water for conditioning, and removal of adults after spawning to prevent egg predation — would offer a reasonable starting framework, drawn from what is known of closely related taxa.
In the aquarium
Ctenobrycon multiradiatus is not an aquarium fish in any practical sense. It does not appear in the trade, has not been documented in hobbyist collections, and carries virtually no profile in hobby literature. The IUCN assessment confirms that no published records of its ecology or natural history exist, which makes it impossible to provide meaningful care guidance.
For aquarists interested in the genus, Ctenobrycon hauxwellianus — the species most often treated as encompassing C. multiradiatus by synonymy — is occasionally encountered and offers the nearest reference point. Ctenobrycon species in general are peaceful, schooling tetras suited to community aquaria with warm, soft-to-moderately-hard water and a varied diet, but these characteristics should be understood as genus-level generalisations, not species-specific data for C. multiradiatus.
Conservation
The IUCN Red List assessed Ctenobrycon multiradiatus as Data Deficient (DD) in 2023 (assessor: Perez, A.; assessment date: 15 January 2021). The Data Deficient rating reflects a complete absence of population data, ecology records, and threat information rather than a demonstration of security: the species is known from a single locality, and it is unknown whether it persists there or at what abundance.
The assessment identifies the confirmed range as the Amazon River at Tefé, Amazonas state, Brazil only. Records from Argentina (Formosa province) and Paraguay have been identified as erroneous, attributed to a read error in Ringuelet et al. (1967), as documented by Koerber (2011). The population trend is listed as unknown. Until targeted field surveys are carried out at and around the type locality and the species' taxonomic standing is resolved — either confirming it as a valid species distinct from C. hauxwellianus or formally sinking it into synonymy — its conservation status and actual risk level cannot be determined.