Taxonomy & naming
Characidium vidali was described by the Brazilian ichthyologist Lauro Travassos in 1967. It belongs to the family Crenuchidae — the South American darters, which also contains the sailfin characins Crenuchus and Poecilocharax — within the order Characiformes. The genus Characidium is large and taxonomically difficult, with many superficially similar, narrow-bodied species distinguished mainly by fine details of banding pattern, scale counts and meristics; Characidium vidali is one of numerous species restricted to small coastal drainages of southeastern Brazil rather than the major Amazon or Paraná systems.
Darter characins like this one are frequently lumped together in the trade under generic names such as "characidium" or "banded darter tetra," and species-level identification of wild-collected fish is often uncertain without voucher specimens. The family name Crenuchidae itself reflects a lineage that behaves more like a benthic darter (in the sense of North American Percidae or Old World gobies) than a typical open-water tetra, which is the key identity point for anyone encountering the genus for the first time.
Morphology
Characidium vidali is a small, elongated, cylindrical fish reaching a documented maximum of about 2.5 in standard length, consistent with the nano scale reported for related species in the genus (C. fasciatum, for example, tops out around 2 in SL). The body is slim rather than laterally compressed like a typical tetra, with a flattened underside well suited to resting on rock and gravel, and fins that are proportionally modest rather than showy.
Colouration in Characidium species generally runs to a base of tan, olive or silvery-brown with a series of dark vertical or blotched bars along the flank — camouflage patterning for a fish that spends most of its time motionless against a mottled substrate rather than a display pattern meant to stand out. Specific published colour-pattern detail for C. vidali beyond this genus-level profile is sparse in the available sources.
Habitat
The species is documented from the northeastern tributaries draining into Guanabara Bay, in Rio de Janeiro state, Brazil — a network of coastal streams distinct from the Amazon and Paraná systems that dominate most South American characin ranges. FishBase classifies it as a freshwater, benthopelagic fish, meaning it lives and forages near the bottom rather than in open water, consistent with the genus's darter habit of perching on submerged stones, wood and leaf litter and making short darting movements between resting points.
Detailed water-chemistry data specific to C. vidali's native streams is not available in the cache; related darter characins from similar coastal Brazilian drainages are typically found in clear, flowing, well-oxygenated water over sand, gravel or rock, and hobby care guidance for the genus (see "In the aquarium") gives a reasonable proxy range.
Feeding
Characidium vidali is a micro-predator. FishBase lists a trophic level of 3.5 for the species, indicating a mid-level carnivore diet, and related Characidium species are documented feeding on chironomid (midge) larvae and other small aquatic and terrestrial insects picked from the substrate. This fits the genus's general profile: darters make short, precise strikes at tiny invertebrates rather than grazing or filter-feeding, and they often ignore dry flake food entirely.
In the aquarium, keepers report that darter characins need small live or frozen foods offered close to the substrate — microworm, baby brine shrimp, chopped bloodworm, daphnia and cyclops are all reported as accepted by the genus — since a fish this size and this feeding style will not compete effectively with faster mid-water tankmates for flake or pellets.
Mating
No species-specific courtship description for Characidium vidali is available in the cache. Across the darter characins (Crenuchidae) as a family, courtship and spawning behaviour is best documented in the sailfin genera Crenuchus and Poecilocharax, which are cave- or leaf-spawners with a brief period of male attendance at the clutch. Characidium itself is reported in aquarium literature as an egg-scatterer, without the cave-guarding behaviour of its sailfin relatives, and detailed pairing or courtship behaviour for this genus is not well documented in the sources available here.
Breeding
Characidium species are generally reported as egg-scatterers, releasing eggs over fine-leaved plants or similar cover rather than building a nest or guarding a clutch — unlike their sailfin relatives Crenuchus and Poecilocharax, which show brief male care at a cave or leaf site. Practical fishkeeping guidance for the genus notes that fine-leaved plants or spawning mops can encourage natural breeding behaviour in aquaria, but detailed, verified breeding accounts specific to Characidium vidali are not available in the current sources — data sparse.
Given the lack of parental-care behaviour documented for Characidium (as distinct from the cave-spawning sailfin genera in the same family), any home breeding attempt should assume no parental care and plan to remove adults from the egg-scatter site to prevent predation on the eggs, following standard practice for scatter-spawning nano characins.
In the aquarium
Characidium vidali suits a small biotope or nano tank rather than a general community aquarium, given its modest maximum size of roughly 2.5 in and its strictly bottom-oriented habits. Practical fishkeeping guidance for the genus recommends keeping darter characins in groups of five or more, since they are shoaling bottom-dwellers that behave more naturally and confidently in numbers; a tank with a mix of open substrate and cover (smooth stones, driftwood, leaf litter) gives them both a hopping ground and retreats.
Hobby sources for the genus report a temperature range of about 72–79 °F and pH 6.0–7.5, which is a reasonable working target absent species-specific water data. Because this is a genuine micro-predator that hunts small invertebrates rather than grazing on flake, keepers should offer small live or frozen foods regularly rather than relying on dry food alone, and should avoid boisterous, fast-feeding tankmates that will out-compete a shy bottom-hopper for food. As a wild-collected coastal Brazilian species rather than a farmed staple, availability in the trade is limited and inconsistent.
Conservation
The IUCN Red List assesses Characidium vidali as Least Concern, with an assessment dated 7 November 2018, though the cache does not include a detailed threat narrative for the species. As a fish restricted to coastal drainages near a major urban and industrial centre — the Guanabara Bay watershed around Rio de Janeiro — habitat degradation, water pollution and urbanisation pressure on these streams are plausible long-term concerns even without a specific published threat assessment, though no such assessment is available in the current sources to confirm this — data sparse.
Because the species is wild-collected rather than commercially farmed for the aquarium trade, any sustained ornamental demand would draw directly on wild populations in a geographically limited range, which is worth noting for keepers even though current IUCN status does not flag the species as threatened.