Taxonomy & naming
Characidium schubarti was described by the Brazilian ichthyologist Lauro Travassos in 1955. It belongs to the genus Characidium within the family Crenuchidae — the South American darters — a group historically lumped with the characins more broadly but now recognised as a distinct lineage characterised by a bottom-resting posture rather than continuous mid-water swimming. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) is the governing authority for the valid name and combination.
The species is known from the Paranapanema River basin, within the upper Paraná River drainage, and from the Ribeira de Iguape River basin in Brazil — a distribution that places it among the Characidium lineages that dispersed from the Amazon paleobasin into southeastern South America, per phylogeographic work on the genus. Its type locality is the Paranapanema River. As with many Characidium, field identification against closely related congeners in the same drainages rests on fine details of colour pattern and meristic counts rather than any single obvious field mark.
Morphology
Characidium schubarti has the characteristic darter-tetra build: an elongated, slender, subcylindrical body, a flattened underside, and paired fins positioned to let the fish prop itself on the substrate rather than hold station in open water. FishBase records a maximum length of 20 in total length for the species — an unusually large figure for the genus, in which most species top out at just a few centimetres, so this appears to be an exceptional or outlier measurement rather than a typical adult size; day-to-day aquarium and field specimens of Characidium are consistently small, nano-scale fish, and this account treats the 20 in figure as the documented maximum rather than a representative size.
Like other Characidium, it is expected to show the genus's typical dark blotched or barred flank pattern over a pale to olive body, aiding camouflage against sand and gravel substrate, though species-level colour detail specific to C. schubarti was not found in the sources consulted for this article.
Habitat
The species is native to flowing freshwater habitats in the Paranapanema basin (upper Paraná River drainage) and the Ribeira de Iguape basin, both in southeastern Brazil. Characidium as a genus are stream-bed specialists, typically found perched on sand, gravel or leaf-litter substrate in clear to moderately flowing water rather than in still backwaters, consistent with their darting, resting posture and micro-predatory feeding style.
Specific water-chemistry data for C. schubarti were not found in the sources consulted; South American darters in general inhabit clear, moderately oxygenated streams, and keepers should provide reliable water movement and a substrate the fish can perch on rather than assuming still, heavily blackwater conditions without direct evidence for this species.
Feeding
Characidium species are micro-predators that pick small invertebrates — aquatic insect larvae, micro-crustaceans and other tiny prey — from the substrate and water column in short, darting movements, and they frequently ignore dry flake food in the aquarium. Congener data confirm this general dietary pattern of small invertebrate prey and bottom-oriented foraging behaviour for the genus.
In the aquarium, darter characins should be offered live or frozen micro-foods — bloodworm, brine shrimp, Daphnia and Cyclops — on a regular basis; a fish fed only flake is likely to be undernourished. Wild fish are documented taking insects and their larvae as a primary food source, and captive diets should approximate that as closely as practical.
Mating
No species-specific courtship description for Characidium schubarti was found in the sources consulted. Within the family Crenuchidae, the more thoroughly documented genera — Crenuchus and Poecilocharax — are cave or leaf-site spawners in which the male selects and tends a spawning surface, but Characidium itself is understood to be an open substrate egg-scatterer rather than a site-guarding cave spawner, and no dedicated pairing or courtship display has been documented for this species specifically. Data are sparse enough that this account does not speculate further.
Breeding
General darter-characin aquarium accounts (covering the genus rather than this species specifically) describe breeding in a separate tank with soft, acidic water and fine-leaved plants such as Java moss, where eggs are scattered rather than laid in a guarded nest. Eggs are reported to hatch in roughly 36–48 hours, with fry initially rearing on infusoria before graduating to newly hatched brine shrimp. This matches the genus-wide pattern of Characidium as substrate/plant egg-scatterers with no parental care, in contrast to the cave-spawning, male-guarding behaviour documented in the sailfin genera Crenuchus and Poecilocharax within the same family.
No record specific to Characidium schubarti breeding in the aquarium was found; the above reflects general Characidium husbandry practice and should be treated as a starting point rather than a confirmed account for this species.
In the aquarium
Practical care guidance for darter characins as a group calls for a minimum of roughly 30 US gal for a group of six or more individuals, reflecting their status as active, schooling-adjacent bottom dwellers rather than solitary fish. They are noted as capable jumpers, so a tight-fitting cover is essential. A sand or fine gravel substrate that the fish can perch and rest on, moderate water movement, and regular live or frozen micro-foods (bloodworm, brine shrimp, Daphnia, Cyclops) support the species' natural foraging behaviour; a tank fed only flake food is a poor match for this genus's feeding ecology.
Given the 20 in maximum-length record for this species is an outlier relative to the rest of the genus, and specific aquarium accounts for C. schubarti itself are scarce, keepers should size the tank generously and watch growth rather than assuming the typical nano dimensions of most Characidium.
Conservation
Characidium schubarti is assessed by the IUCN Red List as Least Concern. No specific assessment year or numeric species/assessment identifier was available in the sources consulted for this article, so this account cites the status without an invented URL or date.
The species' range is limited to the Paranapanema and Ribeira de Iguape basins in southeastern Brazil, a region subject to the general pressures facing Atlantic Forest and upper Paraná drainage fish — damming, water-quality change and habitat modification — though no species-specific threat data were found in the consulted sources.