Taxonomy & naming
Characidium cricarense was described in 2019 by Malanski, Sarmento-Soares, Silva-Malanski, Lopes, Ingenito & Buckup as one of several new darter characins split out of the eastern Brazilian Atlantic Rainforest coastal basins. It belongs to the family Crenuchidae — the South American darters — within the order Characiformes, and to the genus Characidium, whose members are small, elongate, bottom-associated fishes readily distinguished from open-water tetras by their habit of perching on the substrate and darting rather than shoaling in the water column.
The species is placed within the Characidium alipioi species group, a cluster of very similar coastal-basin darters that molecular and phylogeographic work (built on DNA barcodes from dozens of specimens across the region) helped resolve into distinct, basin-restricted species. The specific epithet cricarense refers to the rio Cricaré, the type river for the species; the type locality is the Cachoeira do Inferno rapids on the rio Cricaré near São Mateus, Espírito Santo, Brazil. As with many recently split coastal darters, older literature and databases may still lump populations now assigned to C. cricarense under a broader, older name — the description paper should be treated as the current authority for this population.
Morphology
Characidium cricarense is a small, fusiform, laterally compact fish typical of the genus, with a slightly flattened belly and a body shape suited to holding position against current on rock and gravel rather than cruising open water. The original description gives a maximum size of 2 in standard length, placing it firmly among the smaller darter characins — a genuinely nano-scale fish as an adult.
Colouration is described as understated rather than showy: the head and dorsum are olive-green to light brownish, the flanks are silvery below a darker lateral stripe, and the overall effect is a slightly translucent, camouflaged fish that blends into sunlit rock and gravel rather than standing out. No sexual dimorphism has been documented for the species — males and females are not reliably distinguished by colour or body shape in the source material.
Habitat
Characidium cricarense is a rapids specialist. It occupies the edges of turbulent, fast-flowing lowland rivers and streams, including rocky waterfalls, in a scatter of coastal basins in southeastern Brazil: the Jucuruçu, Itanhém-Alcobaça, Mucuri, Itaúnas, São Mateus and lower Doce systems, all at low elevation (under roughly 656 ft). Within these rivers it favours shallow stretches, generally less than 5 ft deep, over sandy-to-gravel, unconsolidated substrate where it can hold station against the current.
Specific water chemistry data (temperature, pH, hardness) were not captured in available sources for this species — data sparse. As a fast-water rapids fish from warm, lowland Atlantic Rainforest coastal rivers, conditions are presumably well-oxygenated and circumneutral, but no figures should be assumed without a primary measurement.
Feeding
Detailed dietary data for Characidium cricarense specifically were not available in the sources reviewed — data sparse. Characidium as a genus are micro-predators: small-mouthed, bottom-associated fish that pick at tiny invertebrates, insect larvae and micro-crustaceans among rock and gravel, and that frequently ignore flake or other floating foods entirely in favour of foods that sink and move.
In the absence of species-specific feeding studies, the safest working assumption — consistent with the genus and its rapids habitat — is that C. cricarense forages on aquatic insect larvae and small invertebrates picked from the substrate, rather than taking anything from the surface.
Mating
No courtship or pairing behaviour has been documented specifically for Characidium cricarense — data sparse. General accounts of the genus describe substrate spawning between a male and female over sand or fine gravel, but this has not been confirmed for C. cricarense itself, and no sexual dimorphism that would help identify a pair has been reported for the species.
Breeding
Characidium cricarense has no documented aquarium or field breeding record — it is a 2019 description known primarily from taxonomic and phylogeographic survey work, not husbandry literature, so nothing specific can be said about its reproductive mode with confidence. More broadly, Characidium species are generally reported as egg-scatterers over sand or fine substrate with no parental care, distinct from the cave- and leaf-spawning behaviour with brief male care seen in other crenuchid darters such as Crenuchus and Poecilocharax. Whether that pattern holds for C. cricarense specifically has not been confirmed, and this account does not assert a breeding mode for the species beyond that genus-level context.
In the aquarium
Characidium cricarense is not established in the aquarium hobby — it is a very recently described species restricted to a handful of coastal Brazilian rivers, with no meaningful export or captive-breeding history to draw husbandry advice from. Anyone encountering the species, or the closely related and equally obscure members of the C. alipioi group, should plan around the genus's known needs: a river-current setup with a sandy-to-gravel substrate, strong flow and high oxygenation, since these are rapids-edge fish rather than still-water dwellers. Given the tiny maximum size (under 2.5 in SL), it is very much a nano-scale fish, and any tankmates would need to be equally small and non-aggressive.
Because husbandry data for this exact species is essentially absent, prospective keepers should treat any care advice as inferred from the genus rather than confirmed for C. cricarense, and should not assume it tolerates still or warm, low-oxygen water simply because other Neotropical characins do.
Conservation
The IUCN Red List assessment for Characidium cricarense places it in the Least Concern category, with no specific threats identified at the time of assessment. This reflects a moderate distribution across six coastal river basins in Espírito Santo and neighbouring areas of southeastern Brazil, rather than a single-river endemic status.
That said, the Atlantic Rainforest coastal basins the species inhabits sit within one of Brazil's most heavily deforested and developed regions, and rapids-and-riffle specialists like C. cricarense are generally sensitive to changes in flow, sedimentation and water quality even where a formal threat has not yet been documented. As a fish with essentially no aquarium trade footprint, any future conservation concern for this species would stem from habitat pressure in its native rivers rather than collection for the hobby.