Taxonomy & naming
Characidium steindachneri was described by the American ichthyologist Edward Drinker Cope in 1878. It belongs to the family Crenuchidae — the South American darters, which also includes the sailfin characins Crenuchus and Poecilocharax — within the order Characiformes. GBIF's species record confirms the taxonomy and the 1878 authorship without noting any subsequent synonymy or genus reassignment for this species.
Characidium is the largest genus in Crenuchidae, comprising dozens of small, cryptically patterned, bottom-associated species that are frequently confused with one another in the aquarium trade and sold simply as "darter tetra" or "characidium" without a species-level identification. As with many small Neotropical Characidium, field identification of C. steindachneri rests on subtle differences in barring, spotting and fin pigmentation that are easy to lose in casual photographs, so trade specimens should be treated with some caution regarding exact species identity.
Morphology
Characidium steindachneri has the elongate, torpedo-shaped body typical of the genus, built for perching and short bursts of movement along the substrate rather than sustained open-water swimming. FishBase gives a maximum published length of 1.5 in standard length for males and unsexed individuals — a genuinely nano-sized fish — though aquarium reports (Aquarium Glaser) describe specimens reaching roughly 2–3 in, a discrepancy that likely reflects standard-length versus total-length measurement, or larger farmed and well-fed captive fish compared with the wild material FishBase's figure is drawn from.
The pelvic and pectoral fins are enlarged relative to a typical mid-water characin, an adaptation that lets the fish prop itself against wood, stone and leaf litter between darts — the resting, perch-and-dash posture that defines darter behaviour and gives the genus its common name.
Habitat
The species is native to the Amazon and Orinoco river basins, including freshwater drainages of Guyana in northern South America. Within that range it occupies flowing to slow-moving lowland streams and river-margin habitat with a mix of sand, gravel, submerged wood and leaf litter, the structured substrate its perching behaviour depends on.
FishBase records tropical freshwater conditions of roughly 72–77 °F and pH 6.0–6.8 — mildly acidic, moderately soft water rather than extreme blackwater. As a bottom-oriented fish it is closely tied to structure and substrate quality; open, bare-bottomed water offers it neither cover nor foraging opportunity.
Feeding
FishBase describes Characidium steindachneri as omnivorous, with stomach contents dominated by chironomid (midge) larvae and other aquatic insect larvae — the profile of a small, opportunistic invertebrate hunter rather than a grazer or a fish that will readily take flake. This matches the broader pattern for darter characins: they are micro-predators that pick prey items off the substrate and out of leaf litter rather than filter-feeding or schooling up to a food source.
In the aquarium, FishBase notes the species accepts frozen bloodworm, brine shrimp, Daphnia and Cyclops. Practical Fishkeeping's darter-characin care guide likewise emphasises that small live and frozen foods are strongly preferred over dry foods, and that keepers should expect to offer these regularly rather than rely on flake alone.
Mating
Detailed courtship behaviour for Characidium steindachneri is not well documented in the sources available. FishBase notes only that breeding in captivity is possible, without describing courtship display, pairing behaviour or external sexual dimorphism in any detail for this species.
Given the gap in the record, this account does not speculate about courtship specifics. Aquarists attempting to breed the species should expect to observe and document behaviour firsthand rather than rely on an established protocol.
Breeding
As with other Characidium darters, C. steindachneri is understood to be an egg-scatterer over the substrate rather than a nest-builder, cave-spawner or livebearer — consistent with the broader pattern for the genus, in which pairs scatter adhesive or semi-adhesive eggs among fine leaf litter or plant roots with no ongoing parental care. FishBase confirms that captive breeding has been achieved but explicitly notes that detailed breeding protocols are not well documented for this species.
This is a genuine data gap rather than an oversight: unlike the cave-and-leaf-spawning sailfin characins (Crenuchus, Poecilocharax), which have a comparatively well-described breeding routine with brief male care, Characidium species in general — and C. steindachneri specifically — lack a widely published, repeatable home-breeding account. Prospective breeders should treat any attempt as exploratory.
In the aquarium
Characidium steindachneri suits a small to modest species or quiet community tank furnished with fine sand or smooth gravel, driftwood and leaf litter, and enough open substrate for its characteristic perch-and-dart movement. Aquarium Glaser describes the species swimming and resting in tight groups with an engaging, almost dog-like schooling behaviour, so it is best kept as a group of several individuals rather than alone. Practical Fishkeeping's darter-characin guide recommends a calm, lightly stocked setup, since these are not aggressive competitors at feeding time and can be outcompeted by faster, bolder tankmates.
Water should track the mildly acidic, moderately soft conditions FishBase records — roughly 72–77 °F and pH 6.0–6.8 — and, because the species is a genuine micro-predator rather than a flake-eater, keepers should plan to offer small live or frozen foods (bloodworm, brine shrimp, Daphnia, Cyclops, microworm-type foods) regularly rather than depend on prepared dry food. Given its small adult size, it is very much a nano-fish project and should not be housed with tankmates large enough to see it as prey.
Conservation
Characidium steindachneri has not been formally assessed by the IUCN Red List; its status is Not Evaluated. This is common among the many small, widely distributed Characidium species of the Amazon and Orinoco basins, which individually attract little targeted conservation research despite the broader, well-documented pressures facing Amazonian freshwater habitats — deforestation, sedimentation and hydrological change from damming.
No population trend, harvest data or specific threat information for this species was found in the sources consulted. In the absence of an assessment, this account does not speculate about the species' conservation status beyond noting that it remains formally unevaluated.