Taxonomy & naming
Nannocharax elongatus was described by the Belgian-born British ichthyologist George Albert Boulenger in 1900. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) — the standing authority on valid fish names — treats Nannocharax elongatus as a valid species of the Congo River basin, described from the upper Congo between New Antwerp (Makanza) and Boyoma (Stanley) Falls. The West African (Nigeria–Cameroon) populations historically misidentified as N. elongatus were described as a separate species, Nannocharax latifasciatus Coenen & Teugels, 1989, from an affluent of the New Calabar River near Isiokpo, Nigeria.
The genus Nannocharax sits in the family Distichodontidae alongside the much larger, deep-bodied Distichodus and the algae-grazing citharinids, though the resemblance stops at the family level — Nannocharax species are small, elongate, bottom-oriented characins rather than open-water grazers. The epithet elongatus is Latin for "elongated," a reference to the comparatively slender, stretched body form that distinguished Boulenger's specimens from other Nannocharax known at the time.
Morphology
Nannocharax elongatus is a genuinely small fish: FishBase gives a maximum standard length of 2 in for N. latifasciatus, the accepted name covering this population, putting it firmly among the nano characins rather than anywhere near the size of its Distichodus relatives. The body is slender and somewhat cylindrical rather than deep, an adaptation shared across the genus for holding position and hopping along current-swept rocky substrate rather than swimming in open water.
Like other Nannocharax, it likely shows the genus's characteristic countershaded, barred or mottled pattern that breaks up its outline against gravel and stone, though detailed colour and pattern description specific to this population is not available from the cached sources — a gap worth flagging rather than papering over. Fin placement and a slightly subterminal, downward-facing mouth are typical genus traits suited to picking food items off rock surfaces.
Habitat
The type locality is the upper Congo River between New Antwerp (Makanza) and Boyoma (Stanley) Falls, and the species' distribution spans the Congo River basin in Angola, the Central African Republic, the Democratic Republic of Congo and the Republic of Congo — distinct from the West African rivers of Nigeria and Cameroon inhabited by Nannocharax latifasciatus, the species long confused with it. This is a rocky, swiftly flowing river specialist: the genus is characteristically found clinging to and hopping over stony substrate in current rather than in still, vegetated water.
Water across this range is warm, generally clear to lightly tannin-stained, and runs on the soft-to-moderate side of the hardness scale, consistent with a fast-flowing tropical river system rather than a still blackwater swamp. Specific published water-chemistry data for this exact species is sparse; the figures given under Water reflect the pattern documented for the closely related, better-studied Nannocharax brevis and should be read as a genus-level approximation rather than a site-specific measurement.
Feeding
Nannocharax elongatus is best treated as a small insectivore/carnivore rather than a herbivore, in contrast to its plant-shredding Distichodus relatives. Related, better-documented Nannocharax species take small live and frozen foods — bloodworm, Daphnia and similar benthic invertebrates — and forage over rock and root surfaces, picking at epiphyton and small invertebrates rather than grazing plant matter outright. One aquarium-database source on the accepted name N. latifasciatus also notes occasional nibbling at small fish and aquatic plants, but this is a minor, opportunistic behaviour rather than the fish's primary feeding strategy.
In the aquarium, keepers should offer a varied diet of small live or frozen invertebrate foods sized for a fish under 2 in, along with fine sinking foods that let it forage naturally across current-washed decor. Given the limited documentation for this exact species, treat feeding guidance as inferred from the genus rather than confirmed for this population specifically.
Mating
No courtship behaviour specific to Nannocharax elongatus or its accepted synonym N. latifasciatus has been documented in the cached sources. The related, better-studied Nannocharax brevis shows no confirmed breeding account in the hobby either, and the genus as a whole is described as vaguely territorial but generally peaceful when kept in a group with adequate hiding places and visual breaks — behaviour that plausibly extends to courtship interactions, but this is inference from the genus, not an observed account for this species.
Breeding
As with the other Distichodontidae covered on this site, Nannocharax elongatus should be treated as an egg-scattering characin rather than a nest-builder, mouthbrooder or livebearer — but breeding in this species specifically is essentially undocumented. One aquarium-trade source describes the accepted name N. latifasciatus as "easily reproduced" in captivity, but this claim is an outlier against the wider genus pattern, where close relatives such as N. brevis are explicitly reported as not yet bred in the hobby. Given that contradiction and the absence of a detailed spawning account, the honest summary is that breeding protocols for this species are unconfirmed and it should not be assumed to be an easy or reliable captive breeder.
Prospective breeders should expect, at best, a small open-water or scatter-spawning event typical of small riverine characins, with no parental care documented, and should treat any successful spawning as noteworthy rather than routine.
In the aquarium
Nannocharax elongatus is a true nano fish — under 2 in as an adult — and it has essentially no established presence in the aquarium trade; specimens seen under either this name or its accepted synonym N. latifasciatus are uncommon imports rather than a regular commercial staple. A tank for this species should replicate its rocky, current-swept native habitat: a river-style setup with smooth gravel and stone, strong water movement, and driftwood or root structure for cover, rather than a heavily planted, still-water aquascape.
Given its small size and the genus's documented peaceful-but-territorial temperament, it should be kept in a group in a species tank or with other small, calm current-loving fish, never with anything large enough to see it as food. Water should be kept warm and on the soft-to-moderate, mildly acidic-to-neutral side, per the Water figures above. Because so little is documented for this exact species, keepers should treat any care approach as an extrapolation from the wider Nannocharax genus and adjust based on the individual fish's condition.
Conservation
The IUCN Red List currently assesses Nannocharax elongatus as Least Concern. The species — treated by the Catalog of Fishes as a junior synonym of Nannocharax latifasciatus — remains a narrow-range West African river endemic, restricted to a stretch running from the Oshun River in Nigeria to the Cross River in Cameroon, but is not currently considered at elevated risk.
Because this species has essentially no footprint in the aquarium trade, collection pressure from the hobby has never been a meaningful factor in its conservation picture; any environmental pressure on its West African river habitat is not currently significant enough to move the species out of the Least Concern category.