Taxonomy & naming
Nannocharax signifer was described by Moritz in 2010, one of a wave of small West African Nannocharax species resolved from the genus in the early 2000s and 2010s as ichthyologists worked through the region's poorly sampled rivers. It sits in the family Distichodontidae within the order Characiformes, alongside the much larger and better-known Distichodus species and the deep-bodied, algae-grazing citharinids (Citharinus), though Nannocharax itself is a genus of small-bodied, elongate, bottom-associated characins quite unlike either of those relatives in size or habit.
The type locality is the Ouémé River basin in Benin, and GBIF and FishBase both treat N. signifer as a currently valid, distinct species within the genus. The specific epithet signifer is Latin for "standard-bearer" or "flag-bearer," a fitting label for a fish distinguished chiefly by a red-orange marking on the leading edge of its dorsal fin — its "flag." Beyond the original 2010 description, published literature specific to this species is sparse, which is typical for recently described, narrow-range Nannocharax.
Morphology
Nannocharax signifer is a small, slender-bodied characin reaching a maximum recorded length of about 2 in standard length — a genuinely tiny fish even by the modest standards of its genus. Like other Nannocharax, it has an elongate, somewhat cylindrical body built for hugging current-swept substrate rather than an open-water build, with a subterminal mouth suited to picking small prey items off rock and gravel.
The feature that gives the species its name and its best field mark is a red-orange patch on the anterior portion of the dorsal fin, which distinguishes it from other West African Nannocharax species in the same river systems. Beyond that marking and its diminutive size, detailed morphological description is largely confined to the original 2010 taxonomic paper; no separate account of colouration variation, fin formulae or other anatomical detail is available in the cached record.
Habitat
The species is known from the Ouémé River basin in Benin, a tropical West African river system. Recorded habitat is swift-flowing river sections over rocky substrate with marginal vegetation — the kind of well-oxygenated, current-swept water typical of many small benthic Nannocharax across West Africa, rather than the still, blackwater floodplain habitats associated with some other African characins.
Water conditions reported for the Ouémé basin run warm, around 82–84 °F, with a near-neutral pH of roughly 7.0–7.4. That combination — warm, well-aerated, moderately hard, swiftly flowing water — should guide any aquarium approximation of the species' native conditions, since it departs from the softer, more acidic water often assumed for African characins as a group.
Feeding
No diet study specific to Nannocharax signifer has been captured in the record, but the genus as a whole is well characterised as benthic invertivores: fish that pick small invertebrates off the substrate rather than grazing algae or plant material the way their much larger Distichodus relatives do. Related Nannocharax species take small live and frozen foods such as bloodworm and Daphnia readily, and most individuals in the genus are reluctant to accept dry flake or pellet food, at least initially.
Given its tiny adult size and benthic, current-loving habitat, N. signifer almost certainly follows this same pattern — a small-invertebrate specialist rather than an omnivore or herbivore, in clear contrast to the plant-shredding diet that defines its larger distichodontid cousins.
Mating
No courtship behaviour, sexual dimorphism or pairing pattern has been documented for Nannocharax signifer in the available record. The genus generally is not well studied for reproductive behaviour, and this recently described, narrow-range species has, as far as the record shows, not been the subject of any dedicated observation of courtship in the wild or in captivity. Data is sparse; nothing here should be treated as established until a real source documents it.
Breeding
Breeding has not been documented for Nannocharax signifer, and the wider genus offers little precedent: related small Nannocharax species are reported as not yet bred in the hobby, and the closely related, larger Distichodus and citharinid members of the family Distichodontidae are themselves egg-scatterers that are rarely bred at home, with Distichodus in particular considered very difficult to spawn in aquaria. There is no indication of nest-building, parental care or any other specialised reproductive mode in this genus.
Given the total absence of species-specific breeding records, the honest position is that N. signifer's reproductive biology in both the wild and captivity is effectively unknown. Any aquarist attempting to breed it would be working without an established protocol to follow.
In the aquarium
Nannocharax signifer's tiny adult size — under 2.5 in — makes it suitable for modestly sized aquaria, unlike many of its Distichodontidae relatives that demand very large tanks and shred live plants. Related Nannocharax species are described as vaguely territorial toward their own kind but generally peaceful in a group, and they do best with plenty of hiding spots, current, and a rocky, well-oxygenated setup that echoes the swift-flowing sections of the Ouémé basin rather than a still, planted community tank. No fin-nipping aggression has been documented for the genus, and related species are reported as compatible with other peaceful community fish.
A tank replicating the species' recorded native water — warm, around 82–84 °F, near-neutral pH — with a rocky substrate, flow, and small live or frozen invertebrate foods (bloodworm, Daphnia) is the best-supported approach. As with many recently described, narrow-range African characins, N. signifer is essentially unknown in the aquarium trade, and captive-husbandry experience specific to the species has not been documented.
Conservation
Nannocharax signifer has not been evaluated by the IUCN Red List, so it currently carries no formal conservation status. This is unsurprising for a small, recently described (2010), narrow-range species known from a single West African river basin; many such fish simply have not yet been assessed.
As a species apparently confined to the Ouémé River basin in Benin, N. signifer would be vulnerable to any localised pressure on that system — water abstraction, pollution, damming or habitat degradation — but no assessment of population trend or specific threats has been published. Given the narrow known range, ongoing monitoring of West African river systems like the Ouémé is the relevant long-term consideration, even though the species is not currently flagged as threatened.