Taxonomy & naming
Erythrocharax altipinnis was described by Netto-Ferreira, Birindelli, de Sousa, Mariguela & Oliveira in 2013 in a study combining morphological and molecular phylogenetic data. The type locality is the Serra do Cachimbo region of the state of Pará, Brazil — an elevated sandstone plateau in southern Pará that drains to headwater streams of the Tapajós and Xingu systems. The Catalog of Fishes (Eschmeyer, CAS) records the valid name as Erythrocharax altipinnis with the above five-author authority.
The genus Erythrocharax was established in the same work and currently contains this species alone. The authors placed it within Characidae on the basis of both morphological synapomorphies and molecular data, but its precise phylogenetic position within the family remains an active area of inquiry given the notoriously complex internal relationships of Characidae. The species is distinguished from all other characid genera by a suite of unique characters including the form of its jaw dentition and pelvic-girdle morphology, which prompted erection of the new genus rather than assignment to any existing one.
Morphology
Erythrocharax altipinnis is a miniature fish: the maximum recorded standard length is 1 in, placing it at the extreme small end of Characidae and among the tiniest tetras globally. The body is fusiform and laterally compressed in cross-section, the general body form typical of small streamline characins.
Several features mark the species immediately. A conspicuous dark midlateral stripe runs from the opercle all the way to the tip of the caudal fin — an unusually long extent for such a stripe. The adipose fin and caudal fin are bright red in life, a striking contrast with the darker body stripe and the silvery flanks. Males develop notably elongate first rays on the dorsal fin, the character captured in the specific epithet. Meristically, the species shows 11 dorsal soft rays, 24 to 26 anal soft rays, and 34 vertebrae. The jaw teeth are described as pedunculate, notably expanded, and distally compressed in both jaws — a morphology unlike that of most other small characids and one of the primary diagnostic characters that defined the new genus.
Habitat
The known range of Erythrocharax altipinnis is restricted to the Serra do Cachimbo, a sandstone plateau in southern Pará, Brazil. The plateau sits at moderate elevation and is the source of headwater streams draining into the Tapajós and Xingu river systems. These headwater environments are typically clear, low-conductivity, soft and acidic waters characteristic of Amazonian blackwater and clearwater drainages, though specific water-chemistry data for the collection sites of this species have not been published.
The species is classified by FishBase as freshwater, benthopelagic, and tropical. Given the plateau setting and the character of Amazonian highland headwaters generally, the habitat is likely shallow, fast-flowing stream riffle or pool habitat with sandy or rocky substrate, sparse or absent rooted macrophytes, and leaf litter. Precise ecological data — substrate preference, microhabitat use, depth range — remain unpublished as of the time of this writing. The restricted type locality and absence of records elsewhere suggest the species may be a narrow endemic, though survey effort in the Serra do Cachimbo is limited.
Feeding
No dietary study of Erythrocharax altipinnis has been published. The species is listed by FishBase in the same broad trophic category as other small characids of comparable body form, implying opportunistic feeding on small invertebrates — aquatic insect larvae, microcrustaceans, and terrestrial invertebrates falling to the water's surface — as would be expected for a small-bodied, benthopelagic characin in Amazonian headwater streams.
The unusual dentition (pedunculate, distally compressed teeth) may reflect dietary specialization beyond the generalist invertivore pattern typical of the size class, but without gut-content studies this remains speculative. Until field ecological work is conducted, it is not possible to characterize the natural diet more precisely.
Mating
No observations of mating behavior in Erythrocharax altipinnis have been published. As a member of Characidae, and particularly given its small size and general morphology, the species most probably follows the egg-scattering, open-water or plant-associated spawning mode typical of the family: males court females without elaborate nest-building, eggs are scattered among fine-leaved vegetation or substrate, and no parental care is provided.
The elongate anterior dorsal-fin rays present in males are a sexually dimorphic character and likely play a role in display or mate assessment, as elongated fin elements frequently do in small characins. Whether males compete actively or display to females in a manner analogous to other characid species with fin ornamentation is unknown.
Breeding
Breeding of Erythrocharax altipinnis in captivity has not been documented in the published literature or in the hobbyist record accessible to date. Extrapolating from the biology of comparably sized Amazonian microcharacins, spawning would most likely involve adhesive or semi-adhesive eggs deposited among fine-leaved plants or over the substrate, with incubation times in the range of two to four days at tropical temperatures. Adults would not be expected to provide any parental care, and would likely consume eggs if not separated.
Data on clutch size, fry development, and rearing requirements are entirely absent. Given the species' minute adult size, the fry would be exceptionally small and would require the finest of first foods — infusoria or commercial liquid fry preparations — before advancing to newly hatched brine shrimp nauplii. This is largely inference from the biology of related miniature tetras; direct breeding records for this species are needed.
In the aquarium
Erythrocharax altipinnis is essentially unknown in the aquarium hobby. It has not, as far as is documented, entered the ornamental trade in any significant quantity, and no husbandry accounts have been published. Its small size (under 1 in SL) and attractive coloration — red adipose and caudal fins, bold dark lateral stripe — would in principle make it appealing to specialists in microfish and nano aquaria, but until the species is collected, exported, and bred in captivity, practical care information cannot be given.
By analogy with other small, headwater Amazonian characins, soft, slightly acidic, warm water (approximately 75–82 °F) with subdued lighting, fine-leaved plants or leaf litter, and a diet of small live or frozen invertebrates would represent a reasonable starting framework. Any hobbyist working with wild-caught specimens of this species would be contributing genuinely new information to the record.
Conservation
Erythrocharax altipinnis has not been assessed by the IUCN Red List as of the time of this writing. Its conservation status is therefore Not Evaluated (NE). The species is known from the Serra do Cachimbo in Pará, Brazil — a plateau that harbors a number of endemic and range-restricted organisms. The region falls within Brazil's Legal Amazon, where habitat pressures including deforestation, agricultural expansion, and mining activities are ongoing.
The narrow type locality and apparent endemism to a single plateau system are characteristics that frequently correlate with vulnerability in small-bodied freshwater fishes, but without population surveys, range assessments, or habitat-condition data specific to this species, no quantitative conservation assessment is possible. A formal IUCN evaluation would require targeted survey work in the Serra do Cachimbo drainages to establish range limits and population status.