Taxonomy & naming
Rhinopetitia potamorhachia was described in 2014 by André L. Netto-Ferreira, José L. O. Birindelli, Leandro M. Sousa, and Naércio A. Menezes in the Journal of Fish Biology. The valid name, as listed in Eschmeyer's Catalog of Fishes, is Rhinopetitia potamorhachia Netto-Ferreira, Birindelli, Sousa & Menezes, 2014. The type locality is the Rio Teles Pires, a principal tributary of the Rio Tapajós, in the state of Pará, Brazil.
The genus Rhinopetitia was erected by Géry and belongs to the subfamily Stevardiinae within the large family Characidae. A subsequent genus-level revision of Rhinopetitia by Netto-Ferreira and colleagues redescribed the group and added further new species, placing R. potamorhachia alongside R. myersi and the newly described taxa. Rhinopetitia potamorhachia is separated from R. myersi most reliably by its higher premaxillary tooth cusp count of 7–9 (versus 3 in R. myersi), and by the presence of a conspicuous dark midlateral stripe and a humeral blotch that are absent or much weaker in that species.
Morphology
Rhinopetitia potamorhachia is a small fish, reaching a maximum standard length of approximately 2 in in females and 1.5 in in males — typical of the diminutive Stevardiinae body plan shared across many small South American characids. The body is slender and fusiform, as expected of a benthopelagic fish associated with sandy beach margins.
The most diagnostic external features are the dark midlateral stripe running along the flanks and a distinct humeral blotch behind the operculum. These markings set R. potamorhachia apart from R. myersi, which lacks them. Dentition differences are equally important diagnostically: the higher cusp count on the premaxillary teeth (7–9 in R. potamorhachia) is a consistent character used to distinguish this species within genus-level comparisons.
Habitat
The species is known from the Rio Teles Pires, a major right-bank tributary that drains into the Rio Tapajós, itself one of the large clear-water rivers of the Amazon basin system in the state of Pará, Brazil. Additional occurrences have been documented from the Amana National Forest Reserve area in the middle Rio Tapajós, extending the known distribution within that drainage.
FishBase characterises R. potamorhachia as benthopelagic and associates it with sandy beach habitats along stream margins — the shallow, current-exposed sandy edges common along Tapajós-system rivers. The water is tropical freshwater; precise physical and chemical parameters for its specific microhabitats are not well documented in publicly available sources. The type locality within the Rio Teles Pires falls in a region affected by hydroelectric infrastructure development.
Feeding
FishBase records Rhinopetitia potamorhachia as omnivorous, with a trophic level of approximately 2.8 — a value consistent with opportunistic feeding on small invertebrates, organic detritus, and plant material, typical of small characids in sandy-margined streams.
Detailed gut-content studies specific to this species are not available in the public literature. Its benthopelagic habits and small size suggest foraging at or near the substrate and in open water near sandy banks, taking small invertebrates, insect larvae, microcrustaceans, and algal material as they become available.
Mating
No published studies on the reproductive behaviour of Rhinopetitia potamorhachia in the wild are available. As a member of the Stevardiinae — a subfamilial group within Characidae that contains species with diverse reproductive strategies including egg-scattering open spawning and some with insemination — the reproductive mode of this genus has not been characterised in detail in accessible literature.
Based on the general biology of small characids of comparable size and habitat, open egg-scattering spawning with adhesive eggs deposited among fine-leaved vegetation or substrates, and no parental care, represents the most plausible default. Whether the genus shows any of the derived mating features documented in other stevardiine lineages remains undocumented for R. potamorhachia specifically.
Breeding
Rhinopetitia potamorhachia is not established in the aquarium hobby, and no captive breeding accounts have been published or are available in accessible sources. The species is a recently described, little-studied characid from a remote Amazonian drainage, and its captive husbandry remains entirely undocumented.
In the absence of species-specific data, the reproductive biology can only be inferred from the general pattern of small stevardiine characids: egg-scattering spawning over fine-leaved vegetation or sandy substrate, adhesive eggs with no parental care, and relatively small clutches consistent with the fish's small adult size. Any aquarium breeding attempt would require establishing wild-collected stock and working from first principles.
In the aquarium
Rhinopetitia potamorhachia is not present in the ornamental fish trade and has not been maintained in aquaria to any documented extent. It is a scientific specimen species known from museum collections and field surveys rather than a hobby fish. As a small Amazonian characid from sandy clear-water streams, it would theoretically suit a softwater setup mimicking the Tapajós basin environment — warm, slightly acidic to neutral, low-conductivity water with a sandy substrate and moderate current — but this remains speculative.
Aquarists seeking small Stevardiinae species with similar ecological origins are better served by the more established and commercially available members of related genera. Should R. potamorhachia enter the hobby in future, its small adult size of under 2 in SL and inferred peaceful nature would suit a species aquarium or a community of similarly sized, non-competitive South American fishes.
Conservation
Rhinopetitia potamorhachia was assessed as Least Concern (LC) on the IUCN Red List in an assessment dated 18 May 2022, as reported by FishBase. This status reflects the absence of evidence for rapid population decline sufficient to trigger a threatened category rather than a thorough survey of population size or trends; the species is described as poorly documented with limited biological data available.
Of practical conservation concern is the location of the type locality in the Rio Teles Pires, a river that has been the site of significant hydroelectric dam construction. Damming and associated changes to river flow, sediment dynamics, and beach habitats can directly impact benthopelagic sandy-margin species. The extension of the known range to the Amana National Forest Reserve in the middle Rio Tapajós is a positive indicator, as that protected area provides some degree of habitat security for populations within its boundaries.