Taxonomy & naming
Jupiaba elassonaktis was described by Pereira & Lucinda in 2007 from material collected at Peixe, in the Rio Tocantins immediately downstream of the UHE Peixe-Angical dam site in the state of Tocantins, Brazil. The holotype is catalogued as MCP 41465, and the standard length of the holotype is 1.5 in. The species is placed in the genus Jupiaba, a diverse Amazonian and Guiana Shield characid genus whose members share a suite of characters including a distinctive body shape and dentition.
The genus name Jupiaba derives from an indigenous Brazilian word associated with the region where the ichthyologist Angela Zanata — who described several new fishes from the area — was born and worked. The specific epithet elassonaktis is from the Greek, indicating a distinguishing feature of the fin rays; the precise derivation refers to the reduced or fewer fin-ray count that characterises this species relative to close relatives within the genus. Catalog of Fishes records the valid name as Jupiaba elassonaktis Pereira & Lucinda, 2007.
Morphology
Jupiaba elassonaktis is a small, slender characid with a maximum recorded standard length of 1.5 in. The body profile along the anal-fin base is notably posterodorsally slanted, and the caudal peduncle is nearly straight to very slightly concave — features that help distinguish this species from other Jupiaba in the Tocantins basin.
The ground colour is pale yellow, with the dorsum of the head shading to light grey. The colour pattern includes two humeral spots: the first is dark brown and vertically elongate, positioned at approximately the fifth to sixth lateral-line scales; the second spot is very diffuse. The overall impression is of a subtly marked, translucent small tetra, unremarkable in coloration compared with many hobbyist characids but distinctive to the specialist through its body proportions and spot placement.
Habitat
Jupiaba elassonaktis is endemic to the Rio Tocantins drainage of central Brazil. The type locality — downstream of the UHE Peixe-Angical dam in the municipality of Peixe, Tocantins state — lies within a large tropical river system that drains the cerrado and transition forests of central Brazil before joining the lower Amazon via the Tocantins-Araguaia system.
The habitat at the type locality is clear-water riverine environment typical of the middle and lower Tocantins and its tributaries, where water is clear to lightly stained, relatively warm, and associated with submerged structures, roots, and aquatic vegetation in shallow margins. Biogeographic studies of Amazonian characins note that Jupiaba and allied tetras frequent such clear-water igarapés and river margins, sheltering among plants and submerged debris.
Feeding
No published dietary analysis specific to Jupiaba elassonaktis is available. As with most small characids in the genus Jupiaba, the species is expected to be an opportunistic omnivore, taking small invertebrates, insect larvae, microcrustaceans, and plant or algal material in proportion to availability in its riverine habitat.
In the aquarium, small Jupiaba species generally accept standard prepared foods — fine-grade flake and micro-pellets — alongside live or frozen invertebrates such as Daphnia, baby brine shrimp, and micro-worm. A varied diet is advisable for conditioning and maintaining health, though detailed captive husbandry data for this particular species remain sparse.
Mating
No direct observations of mating behaviour have been published for Jupiaba elassonaktis. Based on the biology of the broader genus and small characids generally, the species is presumed to be an egg-scattering open spawner with no parental care, in which males court females among fine-leaved aquatic vegetation or over open substrate, releasing adhesive or semi-adhesive eggs.
Small characids of Jupiaba and related genera in the Tocantins basin are typically fast-moving, alert fish that use structure and vegetation for cover, and spawning is likely triggered by seasonal cues — rising water temperatures and photoperiod — that correspond to the beginning of the rainy season in the cerrado biome. No courtship display or mating behaviour unique to this species has been described.
Breeding
Captive breeding of Jupiaba elassonaktis has not been documented in the literature or in accessible hobby sources. Based on the reproductive biology typical of Jupiaba and allied small characids, breeding would involve egg-scattering over fine-leaved plants or spawning substrate, producing small adhesive eggs that receive no parental attention; adults are likely to consume eggs if not separated.
Given the absence of captive breeding records, specific parameters for temperature, water chemistry, or incubation period cannot be given with confidence. Hobbyists attempting to breed this species would be advised to follow the general approach used for small Amazonian characids: slightly warm, soft-to-neutral clear water, fine-leaved planting or spawning mops, and prompt removal of adults or eggs after spawning.
In the aquarium
Jupiaba elassonaktis is rarely encountered in the aquarium hobby, and essentially no captive husbandry literature exists for it. The species has not appeared as a standard trade item, and its care requirements must be inferred from the biology of the genus and the conditions of its natural habitat in the clear-water sections of the Rio Tocantins system.
As a small, active characid from clear tropical rivers, it would likely do best in a well-filtered aquarium with moderate flow, open swimming space, and some planted structure for cover. Water conditions in the middle range for tropical tetras — around 75–82 °F, pH near neutral, low to moderate hardness — should be appropriate. A group of six or more individuals would suit the species' schooling nature, with peaceful tankmates of similar size. Its lack of hobbyist colour and minimal trade presence mean it remains a specialist's fish for those interested in the Tocantins ichthyofauna specifically.
Conservation
Jupiaba elassonaktis is assessed as Least Concern (LC) on the IUCN Red List, with the assessment dated 07 November 2018. The Least Concern designation reflects that, within the large Rio Tocantins basin, the species does not currently meet the thresholds for a threatened category.
Nonetheless, the Tocantins is one of Brazil's most heavily impounded river systems; the UHE Peixe-Angical dam, immediately upstream of the type locality, is one of several large hydroelectric projects that have fragmented the river, altered flow regimes, and reduced the extent of clear-water habitat available to small characids. Long-term monitoring of the species and the broader Tocantins tetra fauna would be prudent given ongoing infrastructure development in the basin.