Taxonomy & naming
Elachocharax pulcher was described by the American ichthyologist George S. Myers in 1927. It belongs to the family Crenuchidae — the South American darters — within the order Characiformes, and specifically to the subfamily Characidiinae, the group of small, benthic, non-schooling characins that includes Characidium, Melanocharacidium and the other Elachocharax species. The genus Elachocharax itself comprises a handful of tiny, slender darter-characins from Amazonian and Orinoco blackwater and clearwater creeks, distinguished from the closely related Characidium by details of scalation, fin placement and their especially reduced adult size.
Crenuchidae as a whole is often confused with mainstream tetras (Characidae) because both sit within Characiformes, but the darters have a fundamentally different body plan and behaviour — a cylindrical, elongated body, a underslung or subterminal mouth, and pelvic and pectoral fins built for perching and short bursts rather than continuous shoaling swimming. Elachocharax pulcher — the species epithet pulcher is Latin for "beautiful" — is traded under names like "black pygmy darter characin," reflecting its diminutive size and dark, patterned flanks rather than any close relationship to the showier sailfin characins (Crenuchus, Poecilocharax) elsewhere in the same family.
Morphology
Elachocharax pulcher is genuinely tiny: FishBase records a maximum published length of just 1 in standard length, making it one of the smallest described characins in the Amazon basin. The body is slender and elongated, cylindrical rather than laterally compressed, with a small, slightly underslung mouth suited to picking tiny food items from the substrate and leaf litter rather than seizing prey in open water.
Colouration is understated but distinctive at close range: a dark lateral stripe or series of blotches runs the length of the body over a translucent to pale ground colour, giving the fish camouflage against sand and leaf-litter substrates in its native creeks. Like other darters, it lacks the deep body and continuous dorsal profile of a typical shoaling tetra; the fins are comparatively small, built for the short, dart-and-rest movements that give the group its common name rather than for sustained cruising. No reliable external difference between the sexes has been documented for this species.
Habitat
Elachocharax pulcher is native to South America, recorded from the Amazon basin and the upper Orinoco River basin, with a specific collection locality cited from the Rio Nanay in Peru and another cited from the Rio Apaporis in Colombia. Within that range it occupies slow-flowing, shallow forest creeks with sandy or leaf-litter substrates, submerged wood and dense marginal cover — habitat it shares with other tiny darters, pencilfish and dwarf characins rather than the open river channels used by larger characiforms.
Water across its range runs warm and soft to moderately soft, and distinctly on the acidic side: FishBase gives a pH range of roughly 5.4–6.8 and a temperature range of about 75–86 °F, and at least one locality (Rio Apaporis) is cited with a naturally acidic blackwater pH near 6.1. These are classic Amazonian blackwater-to-clearwater forest-stream conditions — tannin-stained, low in dissolved minerals, and structurally complex with leaf litter and root tangles that the fish uses for cover and, per hobby accounts, for spawning.
Feeding
Elachocharax pulcher is a micro-predator, not a grazer or general omnivore in the way many small tetras are. In the wild it almost certainly targets tiny invertebrates — small insect larvae, micro-crustaceans and similar leaf-litter and sediment infauna — consistent with its small, subterminal mouth and its habit of perching and darting rather than actively cruising for food. Hobby sources describe it as an omnivorous micropredator that will accept small frozen foods but does best with live food supplementation, and it is noted as a shy feeder that can be easily outcompeted for food by faster or more assertive tankmates.
In the aquarium this translates into a fish that frequently ignores flake and even many prepared foods, particularly early on. Small live or frozen live-analogue foods — microworm, baby brine shrimp, cyclops, chopped daphnia — are the reliable way to condition it, offered where the fish naturally forages (near the substrate and leaf litter) rather than at the surface.
Mating
Detailed courtship behaviour for Elachocharax pulcher itself has not been documented in the sources available here. Within Crenuchidae more broadly, the darter subfamily Characidiinae is known for pairing rather than mass-spawning behaviour, with a male and female associating briefly around cover — leaf litter, root tangles or fine substrate — rather than the elaborate cave-guarding courtship seen in the family's sailfin characins (Crenuchus, Poecilocharax).
One hobby source notes that this species has been observed spawning in the root systems of floating or terrestrial plants such as Philodendron, suggesting the pair seeks out fine root structure as a spawning substrate rather than open sand or a cleared site. No reliable external sexual dimorphism has been documented for the species; data on this point is sparse and should not be assumed.
Breeding
Elachocharax pulcher is not one of the parental-care sailfin characins of its family — it is a darter in the Characidiinae, the subfamily typified by egg-scattering over fine substrate or fine root structure with no meaningful parental care, in contrast to the brief male cave-guarding seen in Crenuchus and Poecilocharax. The one specific breeding note available places spawning among the fine root systems of floating or terrestrial plants (Philodendron roots are cited), which fits the pattern of a small darter scattering adhesive eggs into cover rather than defending an open nest site.
This is not a species with an established, well-documented aquarium breeding history in the way larger, longer-kept tetras are; data on clutch size, incubation time and fry-rearing specifics is sparse in the sources available here, and breeding reports in the hobby appear to be occasional rather than routine. A heavily planted, slow-flow blackwater setup with fine root structure and leaf litter is the best-documented starting point for anyone attempting it.
In the aquarium
Elachocharax pulcher is a genuine nano species and should be sized and stocked accordingly: a minimum tank size of around 15 US gallons (roughly 15 US gal) is cited by specialist retailers, set up with sand or fine substrate, leaf litter, driftwood and dense planting to replicate its slow-flowing forest-creek habitat. Soft, acidic water in the roughly pH 6.0–7.4 and 75–82 °F range (with FishBase citing a slightly wider 5.4–6.8 pH and 75–86 °F range from wild data) suits it best, and gentle flow rather than strong current matches its natural habitat.
Because it is shy, slow-feeding and very small, this is not a fish for a boisterous community tank — it is easily outcompeted for food and can be intimidated by larger or faster tankmates. Recommended companions are other small, peaceful nano species that share its blackwater preferences, such as Nannostomus pencilfish, Carnegiella hatchetfish, small Hyphessobrycon like H. amandae, and dwarf Corydoras such as C. pygmaeus — fish that will not out-compete it at feeding time. Given its size and shyness, a species tank or a quiet, carefully chosen nano community is the more reliable way to keep it long-term, and live or frozen micro-foods should be offered to ensure it is actually getting fed.
Conservation
The IUCN Red List assesses Elachocharax pulcher as Least Concern, an assessment dated 19 October 2020. This reflects its wide distribution across Amazon and upper Orinoco basin forest streams and the absence of documented major threats specific to the species, rather than any detailed population survey data — as with many small, cryptic Amazonian forest-stream fish, dedicated population monitoring is limited.
The species is collected for the ornamental trade from wild populations, including cited localities in the Rio Nanay (Peru) and Rio Apaporis (Colombia), which places it among the many small blackwater nano fish whose aquarium supply depends on wild collection rather than commercial breeding. Broader pressures on Amazonian and Orinoco forest-stream habitat — deforestation, water-quality change and habitat disturbance — are relevant long-term watch items for this and similar micro-endemic darters, even though the species is not currently classified as threatened.