Taxonomy & naming
Characidium zebra was described by Carl H. Eigenmann in 1909. It belongs to the genus Characidium, one of the largest genera in the family Crenuchidae — the South American darters and sailfin characins — within the order Characiformes. Crenuchidae was long treated as a subfamily of Characidae, but is now recognised as its own family, and Characidium itself is a large, taxonomically active genus with many superficially similar, banded, substrate-dwelling species that are difficult to tell apart without close examination.
The genus name distinguishes these fish sharply from their much more famous relatives in this atlas section: true piranhas, pacus and silver dollars are open-water shoalers or predators in the family Serrasalmidae, while Characidium are small, elongate, bottom-perching darters more closely allied with the gentle, blackwater sailfin characins (Crenuchus, Poecilocharax) than with anything resembling a piranha. The common name "zebra" refers to the dark transverse banding along the flanks that gives the species its most recognisable field mark.
Morphology
Characidium zebra is a small, elongate, torpedo-shaped fish reaching a maximum recorded standard length of 3 in, making it a modestly sized member of the genus rather than a true nano species. FishBase gives a body depth of roughly 3.9-4.8 times the standard length and a head length of about 4.4-4.8 times the standard length, consistent with the slim, streamlined build typical of Characidium darters.
The species carries a series of dark bands or blotches along the body, the hallmark "zebra" pattern from which it takes its name. FishBase notes the fish is highly mimetic: the intensity and contrast of the banding can vary with the colour of the substrate it is resting on, helping it blend into sand or gravel. Like other Characidium, it lacks the deep, laterally compressed body of a piranha or silver dollar, instead having the low-slung, fusiform shape suited to perching on the bottom rather than cruising in midwater.
Habitat
Characidium zebra is a South American species associated with the Amazon drainage, though the exact sub-drainage of its type locality is not fully documented in the sources reviewed here. Like other members of its genus, it is a fish of flowing water rather than still lagoons or backwaters, and FishBase specifically records it living in groups in the upper reaches of rivers, in rapidly flowing water over sandy or rocky substrate.
That habitat — clear, well-oxygenated, current-swept stream sections with a firm sand-and-stone bed — shapes the species' whole way of life: darters like C. zebra perch directly on the substrate using their paired fins, holding position against the current and making short darting movements rather than swimming continuously, an adaptation well suited to riffle and run habitats rather than slow, silty water.
Feeding
Characidium zebra is an insectivorous micro-predator. FishBase records its diet as feeding mainly on insects dug from the substrate or picked directly off rocks, consistent with the foraging style of a fish that spends most of its time perched on or near the bottom rather than hunting in open water.
As a genuine micro-predator of small invertebrates, C. zebra is a poor candidate for a diet of flake alone, and is likely to ignore or underperform on standard dried foods offered as a sole diet. Aquarists should expect to offer small live or frozen foods — bloodworm, brine shrimp, mosquito larvae, and similar substrate-associated invertebrate prey — to keep the species feeding reliably and in good condition.
Mating
No courtship behaviour specific to Characidium zebra was found in the sources reviewed for this article. In the wider genus Characidium, breeding is generally understood to involve egg-scattering over the substrate without the cave- or leaf-spawning behaviour and brief male care documented in its Crenuchidae relatives Crenuchus and Poecilocharax; pairing and courtship displays in Characidium are not well documented in the literature available here.
External sexual dimorphism was not confirmed for this species in the cached sources; as with many Characidium, gravid females may be somewhat fuller-bodied when carrying eggs, but no reliable colour or fin-based distinction between the sexes is documented here.
Breeding
Data on captive breeding of Characidium zebra specifically is sparse in the sources available for this article. Based on what is documented for the genus, C. zebra is presumed to be an egg-scatterer over sand or fine substrate, without the nest-building or parental care seen in its Crenuchidae relatives Crenuchus and Poecilocharax, and without any resemblance to the substrate-nesting behaviour of true piranhas in this atlas section.
There are no confirmed reports in the reviewed sources of C. zebra being routinely bred in home aquaria; hobbyists should treat this as a species that is occasionally kept but not reliably reproduced in captivity, and expect wild or wild-caught stock to remain the normal route into the trade.
In the aquarium
Characidium zebra suits a modestly sized aquarium relative to most fish covered in this atlas section — AquaPortail recommends a minimum volume of around 15 US gal, and the species is described as easy to maintain given appropriate conditions. As a group-living, current-loving darter, it does best with a sandy or fine-gravel substrate, strong water movement, and good oxygenation that echo its native rapids and upper-river reaches, plus several tankmates of its own kind rather than a single specimen.
Because it is a genuine micro-predator that may refuse flake, keepers should be prepared to offer small live or frozen invertebrate foods rather than relying on dried food alone. It is a peaceful, unassuming bottom-dweller with none of the size, aggression or legal complications associated with piranhas or pacus, but its specific current and substrate needs, and its live-food preference, mean it is not a true "set and forget" community fish for less attentive keepers.
Conservation
Characidium zebra has not been evaluated by the IUCN Red List, and no conservation-focused assessment or population data were found in the sources reviewed for this article. As with many small, stream-dwelling Characidium restricted to particular drainages, the species' broader conservation status is effectively undocumented, which is itself a data gap rather than evidence of stability.
No specific threats to Characidium zebra are documented in the sources available here. In general terms, small rheophilic (current-dependent) characins of the upper Amazon drainage face the same broad pressures as other Neotropical stream fish — deforestation-linked sedimentation, water-quality change and hydrological alteration — but none of these have been specifically tied to this species in the sources reviewed.