Taxonomy & naming
Steindachnerina bimaculata was described by the Austrian ichthyologist Franz Steindachner in 1876 as Curimatus bimaculatus, one of many curimatid species he named from Brazilian material during the nineteenth century. It was later transferred to the genus Steindachnerina, a group of small, toothless characins in the family Curimatidae — the curimatas — within the order Characiformes. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) is the governing authority for the valid combination Steindachnerina bimaculata (Steindachner, 1876); this account uses that current genus placement throughout.
The species epithet bimaculata comes from Latin bi- ("twice" or "two") and maculata ("spotted"), referring to a pair of dark spots on the body — specifically at the base of the middle caudal-fin rays and at the base of the dorsal fin. Curimatidae as a family is easy to overlook next to the showier Serrasalmidae piranhas and pacus covered elsewhere in this atlas: its members lack functional jaw teeth entirely, an adaptation tied to their detritus- and algae-based diet rather than to predation or plant-browsing.
Morphology
Steindachnerina bimaculata is a modestly sized, laterally compressed, silvery characin reaching a maximum recorded length of about 7 in standard length — a genuinely small fish by the standards of this atlas's piranha, pacu and wolf-fish entries, and one that poses no risk of outgrowing a reasonably sized aquarium. Like other curimatids it has no functional teeth in the jaws, a family-level trait that reflects its grazing, non-predatory feeding strategy rather than any reduction from a piranha-like ancestor.
The two dark spots referenced in its name — one at the base of the middle caudal-fin rays, another at the base of the dorsal fin — are the most reliable field marks distinguishing it from the many superficially similar Curimatidae and Prochilodontidae species that share its range. Body colouration otherwise follows the typical curimatid pattern: a silvery-white flank with a faint dorsal sheen, unremarkable and cryptic rather than showy, which is consistent with its role as an inconspicuous shoaling grazer rather than a display fish.
Habitat
The species is native to the Amazon River basin and the lower Orinoco River basin, with documented records from Brazil, including lakes near Manaus in the state of Amazonas. As a benthopelagic species it occupies the water column just above the bottom in these lowland Amazonian systems — floodplain lakes, river channels and connected backwaters — habitats that undergo the large seasonal water-level swings typical of Amazonian hydrology.
Dedicated water-chemistry data specific to S. bimaculata was not found in research for this article. Related Curimatidae are broadly documented from warm, soft, mildly acidic Amazonian water in roughly the 75–81 °F and pH 5.5–6.8 range, and it is reasonable to expect S. bimaculata to occupy similar conditions given its shared range and family, but this should be read as an inference from relatives rather than a confirmed data point for this species specifically.
Feeding
Steindachnerina bimaculata has no functional jaw teeth, the defining trait of Curimatidae, and this rules out any predatory or fin-nipping feeding mode. Like other members of its genus and family, it is best understood as an omnivorous grazer that works algae, biofilm and organic detritus off submerged surfaces and substrate rather than pursuing live prey or browsing on plant tissue the way a silver dollar does.
No species-specific aquarium feeding account was found in the sources available for this article, but genus-level care information for Steindachnerina indicates these fish readily accept sinking pellets, flake food and frozen foods in captivity, in addition to grazing naturally on algae and biofilm within the tank. A varied diet weighted toward vegetable and detritus-type foods, rather than a high-protein carnivore diet, is the sensible default for this species pending more specific data.
Mating
No courtship or pairing behaviour has been documented for Steindachnerina bimaculata in the sources available for this article. Nothing specific is known about how mature individuals recognise, court or select mates, and no external sexual dimorphism has been reported — this account does not speculate beyond what is documented.
Breeding
Breeding biology for Steindachnerina bimaculata is not documented. No spawning mode, no aquarium breeding reports and no parental-care behaviour were found in the research for this article, and it should not be assumed to follow any particular pattern from elsewhere in this atlas's characin coverage — it is neither a nest-guarding piranha, nor a farm-bred migratory food fish, nor a confirmed open-water egg-scatterer on direct evidence. The species appears, on current information, essentially unbred in the hobby. Prospective keepers should treat this as an open question rather than assume standard curimatid or generic characin spawning behaviour applies.
In the aquarium
Given a modest adult size of roughly 6.5 in, Steindachnerina bimaculata does not present the tank-outgrowing problems of this atlas's pacus or wolf fish, and a well-established, spacious Amazonian community aquarium should comfortably accommodate it. As a benthopelagic grazer it likely appreciates a mature tank with some algae and biofilm present to forage on, alongside prepared sinking foods, and — following general practice for small shoaling Curimatidae — is best kept in a group rather than alone, though a specific minimum group size for this species was not found in the available sources.
This is not a fish with documentary-driven myths to correct, unlike the piranhas and pacus covered elsewhere in this atlas; it is simply an under-documented, low-profile species. Prospective keepers should expect limited species-specific guidance and treat any care regimen as adapted from its genus and family rather than as confirmed practice for this exact species.
Conservation
Steindachnerina bimaculata has not been assessed by the IUCN Red List and is treated here as Not Evaluated. This is unsurprising for a small, non-commercial curimatid restricted to Amazon and lower Orinoco basin habitats that have not been the subject of targeted population studies. No specific threats to the species were identified in the sources available for this article.
As with many obscure, single-region characins in this atlas, the honest conservation status is simply that not enough is known to assign a meaningful category — a data gap rather than an indication of either safety or risk. Broader Amazonian pressures such as damming, deforestation-linked sedimentation and water-quality change remain relevant long-term watch items for the basin as a whole, as they are for its better-studied relatives.