Taxonomy & naming
Psectrogaster amazonica was described by Carl H. Eigenmann and Rosa Smith Eigenmann in 1889. It belongs to the family Curimatidae within the order Characiformes — a large Neotropical family of small-to-medium, toothless or near-toothless detritivorous characins that includes the curimatas and their relatives, distinct from the Serrasalmidae (piranhas, pacus, silver dollars) and from the true Hemiodontidae, though all three groups share river-shoaling, largely herbivorous-to-detritivorous habits and get lumped together in hobby writing as "minor characins."
The genus Psectrogaster currently holds a handful of valid species distinguished mainly by fine details of squamation, fin-ray counts and mouth position; identification within the genus is a specialist task and not something reliably done from aquarium-trade photographs. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) is the standing authority for the valid name and genus placement used here; nothing in the available sources suggests P. amazonica has been moved out of Psectrogaster since its original description.
Morphology
Psectrogaster amazonica is a compact, laterally compressed, silvery characin reaching a documented maximum of 7.5 in standard length — a genuinely modest adult size, well short of the pacus and true piranhas that share its family-level neighbourhood in aquarium marketing. Like other curimatids it has a small, subterminal or slightly downturned mouth suited to grazing detritus and biofilm off the substrate rather than seizing prey, and a deep but streamlined body built for shoaling in open water over the riverbed.
Detailed published data on colouration, fin-ray counts and sexual differences specific to this species are sparse in the available sources; the genus as a whole is typified by an unremarkable silver body with little of the bold patterning seen in more popular aquarium characins, which is consistent with its role as a food fish rather than an ornamental one.
Habitat
The species is native to the Amazon River basin, including the Tocantins River in northeastern Brazil, and extends into the Orinoco and Essequibo basins, giving it a broad South American range across several major river systems. It is described as benthopelagic, living and feeding near the riverbed while remaining capable of moving up into open water, and it forms large shoals — a behaviour consistent with a fish that is both a significant grazer of the riverbed community and, in turn, an important prey and fishery resource.
Specific water-chemistry data (temperature range, pH, hardness) for P. amazonica were not found in the available sources. As an Amazon-basin river fish it can be expected to experience the region's typically warm, seasonally fluctuating conditions, but no site-specific figures should be asserted without a direct source.
Feeding
Psectrogaster amazonica is detritivorous, feeding on organic detritus, benthic organisms and periphyton scraped from submerged surfaces — the classic curimatid diet that makes this family such effective recyclers of organic material in Amazonian river systems. A related congener, P. essequibensis, has been documented with a degree of dietary flexibility, taking algae and zooplankton alongside detritus, which suggests the genus is not a strict single-food specialist even though detritus and periphyton dominate.
No aquarium feeding data exist for this species, since it is not established in the hobby; any statement about aquarium diet would be speculation rather than sourced fact, so none is offered here.
Mating
No courtship or spawning-behaviour data for Psectrogaster amazonica were found in the available sources. Curimatids in general are understood to be open-water or riverine spawners tied to the seasonal flood cycle typical of Amazonian fish, but nothing specific to this species' courtship, pairing or sexual dimorphism has been documented in the sources consulted, and none should be invented here.
Breeding
There is no documented aquarium or captive-breeding record for Psectrogaster amazonica. The species is fished commercially and for subsistence across its Amazonian range — it is described as common and abundant in the Tocantins River fishery — rather than propagated; like many curimatids it almost certainly spawns in open water in step with the seasonal rise of its home rivers, but the specific breeding mode, fecundity and parental care (if any) are not documented in the sources available for this article.
Given the total absence of aquarium-breeding reports, this is a species where the honest answer is that captive reproduction has not been achieved or recorded, not a fish with a known scatter-spawning routine that can simply be described from the genus in general.
In the aquarium
Psectrogaster amazonica is not an aquarium fish in any practical sense — it does not appear in the ornamental trade, and the sources available describe it purely as a food/fishery species harvested from the Tocantins River and elsewhere in the Amazon basin. A keeper is very unlikely to ever encounter it for sale, and no aquarium care guidance (tank size, water parameters, tankmates) has been published for it.
What can be said with confidence is scale-appropriate: at a maximum of about 7.5 in SL and a natural shoaling, benthopelagic lifestyle, any hypothetical captive setting would need to replicate a large, open-swimming group over soft substrate rather than the planted or decorated aquascape typical of true ornamental characins — but this remains inference from its biology, not documented husbandry, and should be read that way.
Conservation
Psectrogaster amazonica has not been formally assessed by the IUCN Red List and is classified here as Not Evaluated. It is described as common and abundant within the Tocantins River fishery in Brazil, which suggests a healthy, harvestable population at least in that part of its range, but no basin-wide population trend or threat assessment is available in the sources consulted.
As with many Amazonian food fish taken from a broad, multi-basin range (Amazon, Tocantins, Orinoco, Essequibo), the general long-term pressures on the region's rivers — damming, deforestation-linked sedimentation and fishery pressure — are relevant background, but nothing in the available sources indicates this species is currently considered at risk.