Taxonomy & naming
Characidium pteroides was described by Carl H. Eigenmann in 1909, part of a wave of characin descriptions Eigenmann produced from Guiana Shield collections in the early twentieth century. It sits in the genus Characidium within the family Crenuchidae — the darter and sailfin characins — a family whose two subfamilies split sharply in lifestyle: Crenuchinae (Crenuchus, Poecilocharax), the shy, colourful blackwater sailfins prized in the nano-aquarium hobby, and Characidiinae, the much larger group of substrate-perching "darter characins" to which C. pteroides belongs.
The genus Characidium is large and taxonomically active, with species distinguished largely by fine details of colour pattern, scale counts and fin-ray formulae, so field identification within the genus is difficult without a specimen in hand. GBIF and FishBase both list Characidium pteroides Eigenmann, 1909 as the currently accepted combination, with no indication in the available record of a genus-level revision affecting this species; it should not be confused with the aquarium-trade sailfin characins, which are a different subfamily entirely despite sharing the family name.
Morphology
Characidium pteroides is a small, elongate, torpedo-shaped fish — FishBase records a maximum size of just 1 in standard length, making it one of the smaller members of an already diminutive genus. Like other Characidium, it has a slim body, a flattened or subterminal-leaning mouth suited to picking food from the substrate, and the plain, often faintly barred or speckled colouration typical of darter characins, which rely on camouflage against sand and leaf litter rather than display colour.
Detailed morphological description beyond the FishBase summary is sparse in the available record; the species is separated from its many congeners chiefly by meristic and pattern details documented in Eigenmann's original description rather than by any single obvious external field mark.
Habitat
The species is known from the Essequibo River basin in Guyana, on the Guiana Shield of northern South America, where FishBase describes it as a freshwater, benthopelagic fish — living and feeding near the bottom rather than in open water. The type locality is the Essequibo River itself.
Detailed water-chemistry data specific to C. pteroides is not available in the sources consulted; the genus as a whole is associated with clear-to-blackwater Guiana Shield and Amazonian streams with sandy or leaf-littered substrate and cover from wood and low vegetation, consistent with a fish that perches and darts rather than swims in open water.
Feeding
FishBase does not carry species-specific diet data for C. pteroides, but Characidium as a genus are documented micro-predators, taking tiny aquatic and terrestrial invertebrates — insect larvae, small crustaceans and other micro-fauna picked from the substrate and leaf litter — rather than grazing algae or detritus. There is no indication this species departs from that pattern.
In the aquarium, related Characidium are reported to largely ignore dry flake and prefer small live or frozen foods such as bloodworm, mosquito larvae, brine shrimp, daphnia and cyclops; the same is the sound default assumption for C. pteroides absent species-specific data.
Mating
No courtship or spawning behaviour has been documented for Characidium pteroides specifically in the sources available for this account. Related crenuchids show two very different patterns depending on subfamily — Crenuchus and Poecilocharax pair up for cave or leaf-surface spawning with brief male care, while Characidiinae more typically scatter eggs over the substrate — but nothing published ties either pattern to this particular species, so no mating account can be given with confidence.
Breeding
There is no documented aquarium or field breeding record for Characidium pteroides. As a Characidiinae darter rather than a Crenuchinae sailfin, the genus is generally understood to scatter adhesive eggs over sand, gravel or fine plant growth with no parental care, unlike the male-guarded cave spawns reported for its showier relatives Crenuchus and Poecilocharax — but this is an inference from the subfamily's general pattern, not a documented account of this species, and it has not been reported as bred in the hobby.
In the aquarium
Characidium pteroides is not established in the aquarium trade and has no documented care record; general Characidium husbandry, reported for better-known congeners such as C. fasciatum, is the only guide available. Darter characins are strong jumpers and need a tightly covered tank, are best kept in a group of five or more given their naturally gregarious, substrate-perching habit, and do best with a sandy or fine substrate, driftwood, leaf litter and gentle water movement (a sponge-filter outflow is often cited) that mimics a Guiana Shield stream. Given its 1 in adult size, this is unambiguously a nano-tank species, not a community fish for a standard-size aquarium — and given the total absence of trade or captive-care data, it should currently be regarded as effectively unavailable to hobbyists rather than as an aquarium candidate.
Conservation
Characidium pteroides is assessed by the IUCN Red List as Least Concern (2022), consistent with a species restricted to the Essequibo basin that has not been flagged for any specific population decline or habitat threat in the sources reviewed here. As with many small, poorly studied Guiana Shield characins, the absence of documented threats likely reflects limited targeted study of the species as much as it reflects genuine security, and it is not known to be part of the ornamental trade.