Taxonomy & naming
Nannocharax rubrolabiatus was described in 1995 by Van den Bergh, Teugels, Coenen and Ollevier. It belongs to the genus Nannocharax within the family Distichodontidae, the African characin family that also contains the much larger, plant-grazing Distichodus and the deep-bodied Xenocharax. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) is the standing authority for the valid combination Nannocharax rubrolabiatus, and nothing in the available sources suggests a genus change or synonymy for this species — it remains in Nannocharax, the "dwarf darter" genus of small, cryptic, riffle-dwelling African characins.
The species is known only from the Sanaga River basin in Cameroon, and its description sits within a broader mid-1990s effort by Belgian and Cameroonian ichthyologists to resolve the many superficially similar small Nannocharax species found across West and Central Africa's rocky river systems.
Morphology
Nannocharax rubrolabiatus is a genuinely small fish, reaching a maximum recorded standard length of just 2.5 in — modest even by the standards of its own dwarf-bodied genus, and a world away from the size range of its herbivorous Distichodontidae relatives. Like other Nannocharax, it has an elongated, somewhat flattened body plan suited to holding position against current and hugging the undersides of rocks, marked with dark, saddle-shaped blotches along the back and flanks and horizontally elongate spots along the body.
The species' epithet, rubrolabiatus, describes its most distinctive feature: bright red-coloured lips, a field mark that helps separate it from the numerous other small, dark-saddled Nannocharax species found in Central African rivers. Beyond size, colouration and general body shape, detailed morphometric data for this species is sparse in the sources available.
Habitat
This species is endemic to the Sanaga River basin of Cameroon, a large river system draining into the Gulf of Guinea, and has not been recorded outside it. Within the Sanaga, FishBase describes it inhabiting fast-flowing riffle zones of moderately large rivers roughly 98–164 ft wide, sheltering under rocks on a rocky substrate in strong current exceeding 3 ft/second.
Water conditions at documented sites run 73–77 °F with a near-neutral pH of 6.5–7.5, high dissolved oxygen (6.5–7.5 mg/L) consistent with fast, turbulent flow, and low conductivity (35–45 µS/cm) indicating soft, mineral-poor water. This is a specialised riffle habitat rather than the slow, tannin-stained backwaters associated with many other African characins, and the species' entire known range is a single river basin.
Feeding
Specific dietary data for Nannocharax rubrolabiatus was not found in the available sources. Its genus, however, is broadly characterised as made up of small, benthic "darters" that graze algae, biofilm and associated small invertebrates from rock surfaces in fast-flowing water — a very different feeding strategy from the plant-shredding herbivory of its larger Distichodus cousins or the detritus-and-algae grazing of the deep-bodied citharinids.
Given the strong-current, rocky-riffle habitat it occupies, N. rubrolabiatus most likely forages by picking algae, biofilm and small invertebrates from stone surfaces, in keeping with its close relatives, but this should be treated as inference from genus-level habits rather than a documented fact for this particular species; data is sparse.
Mating
No courtship or spawning behaviour has been documented for Nannocharax rubrolabiatus in the sources available. FishBase explicitly notes that breeding behaviour for this species has not been established, and no hobbyist or aquaculture accounts describing pairing, courtship displays or sexual dimorphism were found. Data is sparse for this and closely related small riffle-dwelling Nannocharax species generally.
Breeding
As with most small African Distichodontidae, Nannocharax rubrolabiatus is presumed to be an egg-scattering species typical of its family, but this has not been confirmed for this species specifically, and no reproductive data — wild or captive — is documented in the available sources. It is not known to have been bred in the aquarium hobby, and the general Nannocharax genus is noted as needing planted, fast-flowing tank conditions with no established captive-breeding record for most of its members.
Given the complete absence of documented breeding data, any specific claim about egg number, incubation time or parental care for this species would be speculation. The honest state of knowledge is simply that N. rubrolabiatus has not been bred in captivity, and its reproductive biology in the wild remains unstudied.
In the aquarium
Nannocharax rubrolabiatus is not established in the aquarium trade and essentially never appears for sale; there is no dedicated care record for this species. Its genus relatives, the small Nannocharax darters, are generally kept as planted-tank fish that need strong water movement, high oxygenation, and rocky or driftwood hardscape with hiding places to feel secure — conditions that mirror the fast, rocky riffles this species occupies in the wild.
Given its tiny adult size of just 2.5 in SL, a keeper attempting this species (should stock ever become available) would need a tank sized modestly but with real current — a powerhead-driven "riffle" biotope rather than a still, planted community tank — plus soft, near-neutral, well-oxygenated water in the 73–77 °F range. Because this is essentially unavailable in the trade and undocumented in captivity, prospective keepers should treat any care information as extrapolated from the genus rather than proven for this species.
Conservation
Nannocharax rubrolabiatus is assessed by the IUCN Red List as Vulnerable (VU). As a single-river endemic restricted to the Sanaga basin in Cameroon, it has an inherently narrow range that leaves it exposed to localised pressures — habitat degradation, water-quality change and any future damming or development within the Sanaga system could disproportionately affect a species with nowhere else to go.
The species is not part of the aquarium trade and faces no meaningful collection pressure; its conservation concern stems entirely from range restriction and habitat vulnerability rather than exploitation. As with many small, single-basin African riffle specialists, continued monitoring of Sanaga River water quality and flow regime is the relevant long-term watch item.