Taxonomy & naming
Characidium interruptum was described by the French ichthyologist Paul Pellegrin in 1909. It sits in the genus Characidium, within the family Crenuchidae (the South American darters, or "sailfin characins" in the broader sense used for the family's blackwater specialists), in the order Characiformes. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) is the governing authority for the valid name and combination; nothing in the cached sources for this species suggests a recent reclassification, so it is treated here under its original genus placement.
Characidium is a large genus of small, elongate, bottom-associated darters distributed across South American streams, and species-level identification within the genus is often difficult without close examination of colour pattern and fin-ray counts. C. interruptum has not been the subject of the kind of dedicated phylogenetic or biogeographic study that some of its congeners have received — a 2016 historical-biogeography paper on Characidium examined five species in the genus but did not include C. interruptum, underlining that this remains a comparatively poorly studied member of the genus.
Morphology
Characidium interruptum is a small fish, reaching a maximum recorded standard length of about 2 in, consistent with the genus as a whole — congeners generally range from roughly 1–3 in SL. Like other Characidium, it has the classic darter body plan: an elongate, slightly compressed body, a flattened ventral profile, and a colour pattern of dark blotches or bars over a paler ground colour that breaks up its outline against a gravel or sand streambed. The genus name itself points to this camouflage-driven build, and "interruptum" for this species likely alludes to an interrupted or broken pattern of markings along the flank, though the cached sources do not confirm the specific etymology of the epithet.
Fin placement in Characidium is functional rather than decorative: the pectoral and pelvic fins are positioned to let the fish prop itself against the substrate and hold station in current, the behaviour that gives the group its "darter" name. Detailed measurements beyond maximum length were not available in the cached sources for this species specifically.
Habitat
Characidium interruptum is native to coastal lowland stream systems of southeastern Brazil. FishBase describes it as a tropical, freshwater, benthopelagic species — that is, a fish that lives on or near the bottom rather than in open water — consistent with the genus's general habit of small, clear-flowing streams and lowland rainforest drainages rather than large rivers or standing water.
Specific temperature and pH data for wild populations of this species were not documented in the cached sources. Given the genus's broader habitat pattern of small, shaded forest streams, keepers should approach water chemistry conservatively (see "In the aquarium") rather than assume extreme blackwater conditions without direct evidence for this particular species.
Feeding
Characidium species are micro-predators rather than grazers or generalist omnivores: in the wild and in the aquarium they target tiny invertebrates — small insects and their larvae, mosquito larvae, and micro-crustaceans such as daphnia and cyclops. This is a genus-level pattern documented for Characidium darters in aquarium literature, and it is consistent with the small mouth and bottom-hunting posture of the group.
In captivity, Characidium darters frequently ignore dry flake food and do best on small live or frozen offerings — bloodworm, brine shrimp, daphnia and cyclops. Keepers should expect to feed accordingly rather than rely on flake as a staple; a fish that appears to be starving on flake alone is very often simply refusing a food type it does not recognise as prey.
Mating
No species-specific courtship description for Characidium interruptum was found in the cached sources. In Crenuchidae generally, the family divides into two very different reproductive strategies: the cave/leaf-spawning sailfin characins (Crenuchus, Poecilocharax), where a male attracts a female to a chosen surface and briefly tends the resulting clutch, and the darters proper (Characidium), which by contrast are documented as open substrate spawners with no site-preparation courtship comparable to the sailfin characins.
Aquarium accounts of the genus describe spawning as most likely to occur after a cool water change that mimics a rain event, with a conditioned group in soft, acidic water becoming active around fine-leaved plants such as Java moss — but this is a genus-level pattern from hobby sources rather than a confirmed observation of C. interruptum itself.
Breeding
Characidium, as a genus, are egg-scatterers rather than nest-guarders: the fish scatter adhesive eggs over hard surfaces or fine-leaved vegetation, and the cached sources describe no documented parental care for the group — a clear contrast with their crenuchid relatives Crenuchus and Poecilocharax, which are cave or leaf spawners with brief male care of the clutch. No breeding account specific to Characidium interruptum was found; the following describes genus-level hobby experience with Characidium darters generally, not confirmed observation of this species.
Where Characidium darters have been bred in captivity, hobbyist reports describe clutches of roughly 150 eggs scattered over moss or similar cover, hatching in about 36–48 hours, with fry starting on infusoria before graduating to newly hatched brine shrimp. Given the absence of species-specific data, prospective breeders of C. interruptum should treat this as a starting point drawn from the wider genus rather than a guarantee of this species' exact behaviour.
In the aquarium
Characidium interruptum is a small fish — to roughly 2 in — well suited to a modest aquarium by South American characin standards, but it should not be mistaken for a passive nano community fish. Characidium darters are active bottom-dwellers and capable jumpers, so a tight-fitting lid is essential, and hobby sources recommend keeping them in a group of five or more: like many small shoaling characins, a lone or thinly-stocked group tends to be flighty and hard to observe, while a proper group settles and shows its natural darting, perching behaviour along the bottom.
Because this is a micro-predator that often refuses flake, feeding needs to include small live or frozen foods rather than relying on staple dry food alone (see "Feeding"). A sand or fine gravel bottom with driftwood, leaf litter and some open perching space suits the genus's bottom-hugging habit. Species-specific water chemistry data for C. interruptum was not found in the cached sources; keepers should provide stable, well-filtered, moderate conditions typical of small Brazilian coastal streams rather than assuming an extreme blackwater setup without confirmed data, and should avoid extrapolating housing needs from the larger, showier serrasalmids and pacus that dominate this section of the atlas — this is a small, unobtrusive darter, not a predatory centrepiece fish.
Conservation
Characidium interruptum has not been assessed by the IUCN Red List and is therefore listed as Not Evaluated. This is common among small, range-restricted stream fish from Brazil's coastal lowlands, many of which have never been the subject of a formal conservation assessment despite localised habitat pressure from urbanisation, agriculture and stream degradation along the southeastern Brazilian coast.
No species-specific threat information was available in the cached sources. As with many under-studied Characidium species, the absence of an assessment reflects a lack of data rather than confirmed security, and coastal lowland stream habitat in this part of Brazil is subject to ongoing development pressure generally.