Taxonomy & naming
Characidium lanei was described by the Brazilian ichthyologist Lauro Travassos in 1967. It sits in the genus Characidium within the family Crenuchidae, the darter and sailfin characins, in the order Characiformes. Crenuchidae is a small family split into two very different-looking subgroups: the deep-bodied, often colourful sailfin characins (Crenuchus, Poecilocharax) prized as gentle blackwater nano fish, and the far larger, more numerous darter genus Characidium, whose members are slim, cryptically patterned bottom-perchers found across South American streams from the Andes to the Brazilian coastal ranges.
The species epithet honours John Lane (1905-1963), a Brazilian medical entomologist credited with collecting the type material. Characidium is a taxonomically active genus — many nominal species are difficult to tell apart without close examination of squamation and fin-ray counts — and identification of C. lanei in the field or the trade rests on its coastal-basin distribution and small adult size as much as on colour pattern, which is a fairly typical dusky-barred darter livery shared with several close relatives.
Morphology
Characidium lanei has the classic darter build: an elongated, slender, only mildly compressed body, a straight dorsal profile, and a small, slightly subterminal mouth suited to picking prey items off the substrate rather than pursuing them in open water. The pelvic and anal fins are proportionally robust — the fish rests its weight on them when perched on gravel or wood, in the same way a goby or hillstream loach does, a convergent posture shared across unrelated "darting" fish that live in fast water.
FishBase records a maximum published size of 2.5 in standard length for wild specimens, making this one of the smaller members of an already modestly sized genus. Colouration follows the general Characidium pattern: a pale to olive-brown ground colour broken by a dark lateral stripe or series of blotches running the length of the body, which provides camouflage against mixed gravel and leaf-litter substrates rather than any striking ornamental colour.
Habitat
The species is native to coastal river basins of southeastern Brazil, with records concentrated around the Ribeira de Iguape River system near its type locality. Like other Crenuchidae darters, it is associated with flowing water — streams and river reaches with a rocky or mixed gravel-and-leaf-litter substrate, rather than still lentic habitat — and it is a benthopelagic species, living in close association with the bottom rather than schooling in midwater.
Specific water chemistry data for C. lanei itself is sparse, but the family account for Crenuchidae darter characins generally describes fast-flowing, well-oxygenated water near rapids and riffles, water temperatures around 18-24 degrees C, and a soft to moderately hard, mildly acidic to neutral pH range of roughly 5.6-7.5 — cooler and better-oxygenated conditions than the warm floodplain water associated with many other Neotropical characins, reflecting the family's affinity for flowing headwater and coastal-range streams rather than blackwater or lowland floodplain systems.
Feeding
Characidium lanei is a micro-predator, not an omnivorous grazer or a flake-eating community fish. In the wild it picks tiny invertebrates — aquatic insect larvae, micro-crustaceans and other benthic invertebrates — off the substrate and out of the current, consistent with its perching, ambush-style posture. The Fishipedia trade account notes that aquarium specimens can be trained onto dry foods such as flakes and pellets alongside fresh and frozen items, but this reflects an adaptable captive diet rather than the fish's natural feeding ecology, and newly imported or shy individuals often ignore flake entirely at first.
In the aquarium, small live and frozen foods sized to the fish's small mouth — microworm, baby brine shrimp, chopped bloodworm, small cyclops — are the most reliable way to get a darter feeding well, especially early on. Feeding should be offered where the fish naturally forages, near the substrate and in current, rather than at the surface.
Mating
Detailed courtship behaviour specific to Characidium lanei has not been documented in the available sources. In Crenuchidae more broadly, courtship in Characidium species is described as a pair coming together at the substrate: the pair positions itself side by side near the bottom ahead of spawning, in contrast to the cave- or leaf-guarding courtship seen in the sailfin characins Crenuchus and Poecilocharax. No reliable external sexual dimorphism for C. lanei is recorded in the cache; darters of this genus are generally difficult to sex by eye outside of gravid condition in females.
Breeding
Characidium species, including C. lanei, are egg-scatterers rather than nest-builders or mouthbrooders — this places them apart from their sailfin cousins Crenuchus and Poecilocharax, which are cave- or leaf-spawners with brief male care of the clutch. A spawning pair scatters adhesive eggs over hard substrate at the bottom of fast-flowing water, with no parental care of the eggs or fry documented for the genus.
Captive breeding of C. lanei specifically is not documented in the available sources, and the Fishipedia trade account notes that breeding mode has not been recorded in the aquarium hobby for this species. The wider family account describes captive breeding of darter characins as rare but achievable in river-style setups that replicate strong flow and high oxygenation; fry, where reared, would be expected to need infusoria followed by baby brine shrimp nauplii, as with other small scattering characins. This species should be treated as essentially unbred in the hobby until better records emerge.
In the aquarium
Characidium lanei is a small, current-loving nano fish, and the single most important thing to get right is water movement and oxygenation rather than tank size. Fishipedia's trade account specifically recommends oversized filtration — on the order of 10-20 times the tank volume per hour — to recreate the fast, well-oxygenated flow the species is adapted to; a still, low-flow community tank is the wrong environment for a darter no matter how peaceful it is with tankmates.
Described as peaceful and suitable for a community setting, it does best with a fine gravel or mixed gravel-and-leaf-litter substrate to forage over, driftwood and smooth stones to perch on, and tankmates that will not outcompete it at the bottom for the small live and frozen foods it needs. Because it is a micro-predator that may initially refuse dry food, keepers should be prepared to offer live or frozen foods, especially with newly acquired fish, and should not assume a darter is thriving just because it accepts flake — watch for actual bottom-foraging behaviour and body condition instead.
Conservation
Characidium lanei is assessed by the IUCN Red List as Least Concern, with the assessment dated 7 November 2018. The available sources report no specific population decline or major documented threat for the species. Its range within the coastal river basins of southeastern Brazil, including the Ribeira de Iguape system, places it in a region subject to the general pressures facing Brazilian Atlantic coastal watersheds — deforestation, water-quality change and habitat modification — though none of these are flagged as an active concern for this species in the current assessment.
As with many small, non-flagship characins, C. lanei's conservation profile benefits from a lack of targeted collection pressure: it is not a major aquarium-trade staple, and its Least Concern status most likely reflects a genuinely stable population within a still largely intact set of coastal drainages rather than heavy monitoring.