Taxonomy & naming
Serrapinnus aster was described by Luiz Roberto Malabarba and Daniel Jerep in 2014 in a revision of the genus Serrapinnus from the Rio Tocantins-Araguaia basin. The work treated three new species, of which S. aster is one. The holotype, MZUSP 115012 (1 in SL), is deposited at the Museu de Zoologia da Universidade de São Paulo. Eschmeyer's Catalog of Fishes recognises the valid name as Serrapinnus aster Malabarba & Jerep, 2014.
The genus Serrapinnus belongs to the family Characidae and comprises small, slender characids distributed across South American river systems. The specific epithet aster is Latin and Greek for star, most likely alluding to the distinctive semicircular arrangement of the ventral procurrent caudal-fin rays, a derived character unique to males of this species within the genus.
Morphology
Adults reach a maximum of approximately 1.5 in standard length, placing S. aster among the smaller members of its genus. The body is slender and laterally compressed in the typical Serrapinnus fashion, with eight branched dorsal-fin rays. Premaxillary dentition consists of 7–9 cusps on each tooth, a count shared with several congeners but useful in combination with other characters.
The most immediately striking feature is the male-specific modification of the ventral procurrent caudal-fin rays, which are enlarged and scimitar-shaped, curving into a broad semicircle. No other species of Serrapinnus in the Tocantins drainage shares this character, making it a reliable field mark for males. A dark lateral stripe runs from the posterior margin of the orbit through the flank to the median caudal rays, a feature common across many small characids but consistent in this species.
Habitat
Serrapinnus aster is known from tributaries of the Rio Tocantins basin in Brazil, one of the major river systems of the Brazilian interior that drains northward into the Amazon estuary. The original description places it in this drainage basin alongside two other newly described congeners, suggesting a degree of ecological radiation within the system.
FishBase records the species as freshwater and benthopelagic, indicating it occupies the water column from near the bottom upward in lentic or lotic environments. No detailed water-chemistry parameters were published in the original species description's abstract. General conditions inferred from the Rio Tocantins basin — a tropical, seasonally variable system — suggest warm, soft-to-moderately-hard freshwater with a trophic level of 2.6 (FishBase), consistent with invertivore-leaning omnivory.
Feeding
With a trophic level of 2.6 recorded by FishBase, Serrapinnus aster feeds low on the food chain as a small invertivore or omnivore. Small aquatic invertebrates, microcrustaceans, and organic detritus likely comprise the bulk of the natural diet, as is typical for small characids of similar body size in South American river systems.
No dedicated feeding study for this species is known. By analogy with its congeners and the broader Serrapinnus assemblage, it is expected to be an active, opportunistic feeder that takes whatever small items are available in the water column and near the substrate.
Mating
No specific mating observations have been published for Serrapinnus aster. As a characid, it almost certainly practices egg-scattering open spawning without parental care, the reproductive mode that prevails across the family. Males of this species possess the sexually dimorphic scimitar-shaped ventral procurrent caudal-fin rays, suggesting that these structures play a role in courtship or spawning behaviour, though their precise function has not been formally described.
By comparison with other small characids, courtship likely involves male display behaviour in which the modified caudal structures are exposed to rival males or prospective females. Spawning probably occurs among fine-leaved aquatic vegetation or over the substrate, with adhesive or semi-adhesive eggs deposited in small batches.
Breeding
No captive breeding accounts for Serrapinnus aster have been published, reflecting its absence from the mainstream aquarium trade. The species was described only in 2014 and has not been imported commercially to any documented extent.
As a small, open-water egg scatterer in the Characidae, breeding requirements are expected to follow the general small-characid pattern: slightly soft, warm water, fine-leaved plants or spawning mops as egg substrate, and removal of adults after spawning to prevent egg predation. Fry would require very small initial foods. Until dedicated observations become available, husbandry inferences remain extrapolations from the family.
In the aquarium
Serrapinnus aster does not appear to be established in the aquarium trade. No commercial importers or hobbyist care guides are known for this species, which was described only in 2014 and remains a scientific rarity. Any specimens that do enter the trade would most likely originate from targeted collection expeditions in the Rio Tocantins drainage rather than commercial breeding operations.
Should the species become available, general Serrapinnus husbandry would apply: a small species suited to a planted nano or species tank, soft and slightly acidic tropical water around 75–82 °F, kept in groups so that the males' modified caudal structures can be observed during social interactions, and fed a varied diet of small live and frozen invertebrates alongside quality micro-pellets or flake. Its small size (1.5 in) and likely peaceful temperament make it compatible with other small, non-aggressive fish.
Conservation
FishBase records Serrapinnus aster as Least Concern based on the 2018 assessment cycle, reflecting that the species does not currently meet the thresholds for a threatened category. The Rio Tocantins basin, where the species occurs, is a large and still substantially intact river system, though it faces pressure from hydroelectric development — the Tucuruí dam and its reservoir represent the most significant alteration in the lower basin — and ongoing deforestation in the cerrado and Amazon transition zone.
Because S. aster was described only in 2014 and detailed distributional surveys within the basin are incomplete, the full extent of its range and any subpopulation structure are not well characterised. Continued monitoring of the Tocantins tributary fauna and the long-term effects of basin-scale hydrological change on small, possibly range-restricted characid species will be important for keeping the conservation status current.