Taxonomy & naming
Psectrogaster curviventris was described by Carl H. Eigenmann and William R. Kennedy in 1903. It belongs to the family Curimatidae — the toothless characins, sometimes called curimatas — within the order Characiformes. Curimatidae is one of several families carved out of the old broad "characin" grouping and is distinguished from its relatives by the near-total loss of jaw teeth, an adaptation tied to its members' detritivorous, substrate- and biofilm-grazing feeding mode rather than to predation or browsing on plant matter.
The genus Psectrogaster itself is a small, taxonomically stable group of South American curimatids; the Catalog of Fishes (Eschmeyer, California Academy of Sciences) is the reference point for its currently valid species and this account follows that placement without alteration. Data on this particular species' taxonomic history beyond its original description is sparse in the cached sources, and no synonymy or generic reassignment is asserted here.
Morphology
Psectrogaster curviventris reaches a maximum recorded size of 6.5 in standard length, making it a small to modestly sized member of its family — nowhere near the bulk of its Curimatidae relatives such as Prochilodus, and a useful contrast with the much larger food-fish migrators covered elsewhere in this atlas section. As a curimatid it carries the family's hallmark toothless, protrusible, downward-oriented mouth adapted for grazing detritus and biofilm from submerged surfaces and sediment, rather than the bladed dentition of a piranha or the crushing molariform teeth of a pacu.
Beyond the confirmed maximum length, the cached sources do not provide further morphometric detail (body depth, fin counts, colouration) for this species specifically, so this account does not speculate beyond what curimatids share as a family: a laterally compressed, silvery body typical of open-water and floodplain shoaling characins.
Habitat
Psectrogaster curviventris is native to lowland South American river systems, with documented distribution spanning the Río de la Plata system, the Rio Madeira in the southwestern Amazon basin, the Araguaia-Tocantins basin, and the Paraguay basin. This is a genuinely wide cross-basin range for a single curimatid species, and phylogeographic work on the family places its divergence from a Paraguay-basin ancestor at roughly 1.6 to 4.5 million years ago, spanning the Pliocene and Miocene — consistent with a long-established lowland lineage rather than a recent, narrow-range endemic.
As a lowland river and floodplain species, it is reasonable to expect it in slow-flowing channels, floodplain lakes and similar warm, seasonally fluctuating habitats typical of the Paraná-Paraguay and southwestern Amazonian drainages, though the cached sources do not give specific water-chemistry measurements for this species. No blackwater or extreme-parameter claim is made here in the absence of that data; readers should treat detailed water chemistry as unconfirmed pending better sourcing.
Feeding
Psectrogaster curviventris is a detritivore and biofilm/algae grazer, consistent with the toothless, downturned mouth typical of its family. Curimatids in general feed by sifting fine organic detritus, algae and biofilm from sediment and submerged surfaces rather than by taking live prey, seeds or fruit in the manner of many other Characiformes covered in this atlas.
Beyond the general family-level feeding mode, the cached sources note that detailed dietary data specific to this species is sparse. No aquarium feeding protocol can be given with confidence, since the species has no documented hobby husbandry history (see "In the aquarium").
Mating
No courtship or pairing behaviour has been documented for Psectrogaster curviventris in the cached sources. Data on reproductive behaviour in this species is sparse, and this account does not speculate about courtship, spawning triggers or sexual dimorphism beyond what is confirmed: no external sexual dimorphism is documented for this species.
Breeding
Breeding biology for Psectrogaster curviventris is not documented in the cached sources, and the species is not known to be bred, or even regularly kept, in home aquaria. Rather than assign it a breeding mode by analogy to better-studied relatives, this account states plainly that the mode, fecundity, parental care and developmental timeline are unconfirmed for this species. Wild reproduction almost certainly follows the broad river-floodplain pattern common among Neotropical lowland characins, but no source-backed detail is available to describe it specifically.
In the aquarium
Psectrogaster curviventris has essentially no track record in the aquarium hobby. It does not appear in the trade under a common name, and no husbandry, tankmate or aquascaping guidance specific to this species could be confirmed from the cached sources — a direct FishBase husbandry lookup returned no usable content. Prospective keepers should not treat this as a beginner or readily available species; it is, at best, an occasional incidental catch alongside other South American lowland characins rather than a fish sought out or bred for the trade.
What can be said with confidence, based on its family and modest confirmed size of 6.5 in SL, is that it would be a peaceful, non-aggressive detritivore/grazer suited in principle to a shoal in a large, well-planted or driftwood-furnished South American community setup — but this is an inference from its family biology, not a documented care regime, and should be treated accordingly.
Conservation
Psectrogaster curviventris is assessed by the IUCN Red List as Least Concern. This reflects its unusually wide distribution across multiple major South American drainages — the Río de la Plata system, Rio Madeira, Araguaia-Tocantins and Paraguay basins — which spreads any single localised pressure across a broad total range rather than concentrating risk in one river system.
No species-specific threats are documented in the cached sources. As with many widespread, non-commercial lowland characins, the general pressures facing South American freshwater systems — damming, deforestation-linked sedimentation and water-quality change — are the relevant long-term watch items, even though the species itself is not currently considered threatened.