Taxonomy & naming
Nannocharax ansorgii was described by the Belgian-British ichthyologist George Albert Boulenger in 1911. It sits in the genus Nannocharax within the family Distichodontidae — the African characin family that also contains the far larger, deep-bodied Distichodus grazers and the food-fish citharinids — and the Catalog of Fishes (Eschmeyer, California Academy of Sciences) is the reference for the currently valid combination.
Nannocharax is a large, taxonomically active genus of small, elongated, bottom-associated African characins, and species-level identification within it is difficult and easily confused without a specimen in hand; the little available literature on N. ansorgii treats it as a valid, distinct species rather than a synonym. GBIF's taxonomic record confirms the name, the family placement and the 1911 Boulenger authority used here.
Morphology
This is a genuinely small fish: FishBase records a maximum of 1.5 in standard length for males and unsexed individuals, corresponding to roughly 2 in total length — smaller than many popular nano fish. Like other Nannocharax, it has an elongated, slightly flattened-bellied body built for holding station against current rather than for open-water cruising, a feature it shares by convergence with the unrelated South American darter genus Characidium.
Detailed colouration and fin-pattern data were not found in the sources consulted for this article; keepers researching identification should rely on a dealer's confirmed provenance rather than photographs of similar-looking congeners, since the genus is notoriously difficult to sort out visually.
Habitat
Nannocharax ansorgii is native to West and Central Africa, with FishBase distribution records spanning the Senegal, Gambia, Niger and Volta river basins. Within these systems it occupies swiftly flowing sections of stream and river — a darter's habitat, holding position on or near gravel, stone and coarse substrate rather than schooling in mid-water.
FishBase gives tropical water conditions of roughly 72–79 °F and pH 7.0–7.8, meaning this species runs in cooler, closer-to-neutral water than many of the soft, warm, acidic conditions associated with Congo basin characins — a reminder that "African river water" varies considerably by drainage, and that this particular species is not a blackwater fish by the data at hand.
Feeding
FishBase describes Nannocharax ansorgii in the wild as a small carnivore feeding on small insects, supplemented by algae grazed from the substrate it holds station on. This matches the broader pattern in Nannocharax and in the related Seriously Fish profile of N. brevis, which describes the genus as carnivorous and dependent on small live or frozen foods in captivity.
In the aquarium, keepers should plan on small live and frozen invertebrate foods — items like Daphnia, Artemia and finely chopped bloodworm-scale fare — sized for a fish under 2 in, rather than the vegetable-heavy diet appropriate for its much larger Distichodus relatives.
Mating
No courtship or spawning behaviour for Nannocharax ansorgii was found in the sources consulted for this article. Data is sparse for the genus as a whole in aquarium literature, and nothing specific to sexing or pairing this species can be reported without risking invention; this should be treated as an open question rather than a settled account.
Breeding
Breeding has not been established for Nannocharax ansorgii in the sources reviewed here, and the related-genus profile for N. brevis on Seriously Fish specifically notes that Nannocharax species are rarely bred in captivity. Distichodontid characins in general — including the larger Distichodus — are egg-scatterers that are notoriously difficult to spawn in a home tank, and small darter-type Nannocharax appear to follow that same pattern rather than any form of nest-building or parental care.
Given the total absence of documented spawning accounts, prospective keepers should not expect to breed this species and should treat any wild-collected or farmed stock as effectively non-renewable within the hobby.
In the aquarium
Nannocharax ansorgii is sized for a genuinely small setup relative to most characins on this site — a mature adult tops out around 2 in — but its habitat requirements are specific: it is a current-loving, substrate-oriented darter, not a schooling mid-water fish, so it needs flowing water, oxygen-rich conditions, and a gravel or stone substrate to hold station on rather than the dense planting favoured by many small characins. The related N. brevis profile on Seriously Fish reinforces that the genus wants cooler, well-oxygenated, flowing tropical water rather than a static, warm community tank.
This species is essentially unestablished in the aquarium trade: it is rarely offered, has no meaningful captive-breeding record, and is a poor choice for anyone wanting a self-sustaining population. Anyone who does source it should keep expectations modest, prioritise water movement and oxygenation over decor, and avoid mixing it with boisterous tankmates that could outcompete a small, current-holding insectivore for food.
Conservation
Nannocharax ansorgii is assessed by the IUCN Red List as Least Concern, consistent with a species distributed across multiple West African river basins (Senegal, Gambia, Niger, Volta) rather than confined to a single threatened waterway. This is a wide-ranging, currently secure species by the available assessment, not a narrow-range endemic under known pressure.
As with many small, non-commercial African characins, it is not a species with a significant aquarium trade footprint, and broader watch items for its river systems — damming, agricultural runoff and habitat degradation across West African drainages — are general regional concerns rather than documented species-specific threats in the sources reviewed here.