Taxonomy & naming
Nannocharax procatopus was described by the Belgian-based ichthyologist George Albert Boulenger in 1920. It sits in the genus Nannocharax, a large assemblage of small, slender, bottom-associated African characins placed in the family Distichodontidae — the same family that contains the far larger and more heavily traded Distichodus species and the deep-bodied, algae-grazing citharinids are its close relatives at the family level, classified in the neighbouring family Citharinidae. Despite the shared family lineage, Nannocharax is built and behaves nothing like the plant-shredding Distichodus: it is a small, cryptic, substrate-picking fish rather than an open-water grazer.
The genus name Nannocharax combines the Greek nannos ("dwarf") with charax, the classical root shared by many characin genus names; procatopus is a Latinised epithet whose exact derivation is not recorded in the sources consulted here, though it echoes the unrelated killifish genus name Procatopus, likely reflecting a superficial resemblance Boulenger noted between the two groups rather than any close relationship. As with many small, poorly studied Congo basin characins, N. procatopus is rarely revised and its taxonomic history is thin in easily accessible literature; the species remains valid under the Catalog of Fishes.
Morphology
Nannocharax procatopus is a small, elongated, somewhat flattened-bellied characin reaching a maximum recorded length of about 3 in total length in males and unsexed specimens, with a more typical adult size around 2.5 in TL — and aquarium specimens are usually reported near 2.5 in. The body is dark brown overlaid with a scatter of lighter spots along the flanks, a cryptic pattern consistent with its habit of resting and foraging low in the water column over sediment and leaf litter rather than swimming in open water.
Like other Nannocharax, the body plan is more elongated and less laterally compressed than the deep-bodied Distichodus, and the mouth is small and subterminal, suited to picking small food items off surfaces rather than grazing or biting plant matter. No reliable account of external sexual dimorphism has been documented for this species.
Habitat
Nannocharax procatopus is native to the middle Congo River basin in Central Africa, with records spanning the Dja River in the Sangha drainage of Cameroon, the Luachimo River (a Kasai tributary) in Angola, and the Kasai, Uélé, Ruki, Aruwimi, Itimbiri and Lindi-Tshopo systems and the Wagenia Falls area in the Democratic Republic of the Congo. It is a freshwater, demersal species, living on or near the bottom of these river systems.
Water across this range is warm and only mildly acidic to neutral: FishBase records a pH range of roughly 7.0 to 7.5 and a tropical temperature range of about 68–75 °F. That combination — moderate pH close to neutral rather than the deeply acidic blackwater associated with some Congo tributaries, paired with relatively cool tropical temperatures for a characin — should guide aquarium water chemistry more than assumptions drawn from South American characins.
Feeding
In the wild, Nannocharax procatopus feeds on small insects and algae picked from the substrate and surfaces within its river habitat, consistent with its benthic, bottom-oriented lifestyle. It is not a plant-shredding grazer in the manner of its larger Distichodus relatives; its diet leans toward small invertebrate prey supplemented with algal material.
In the aquarium, hobby sources report that it takes live and frozen foods such as bloodworms and Daphnia readily, but does not take dry flake or pellet food well. A keeper wanting to maintain this species should plan on a live/frozen-food-based diet with some algae or vegetable matter available, rather than relying on prepared foods.
Mating
No courtship behaviour has been documented for Nannocharax procatopus in the sources available. Sexual dimorphism is not reliably described either — hobby accounts note it as unknown — so there is currently no established way to visually distinguish males from females in this species.
Breeding
Breeding in Nannocharax procatopus is not documented in captivity. Like most small African Distichodontidae, it appears to be an egg-scattering species by family-wide pattern, but no spawning account, egg description, or fry-rearing report exists in the sources reviewed here, and the species has essentially no track record of being bred in the hobby. Prospective keepers should treat any home-breeding attempt as unexplored territory rather than something with an established protocol.
In the aquarium
Nannocharax procatopus is a small, peaceful, gregarious fish reported to reach around 2.5 in in aquarium conditions, making it suitable for a modestly sized species or community tank rather than anything oversized. It should be kept in a group rather than alone: hobby accounts describe it as shy and prone to stress when kept singly or without cover, and a settled group is calmer than isolated individuals.
Given its native water — moderate pH near neutral (roughly 7.0–7.5) and cooler tropical temperatures (about 68–75 °F) rather than warm, soft blackwater — the tank should offer a soft substrate, leaf litter or fine sediment for foraging, subdued lighting and plenty of cover from wood or plants to reduce stress. Because it reportedly refuses dry food, keepers need to commit to regular live or frozen foods such as bloodworms and Daphnia. This is not a fish that has been widely tested in home aquaria, so its long-term care requirements are less well established than for many popular characins.
Conservation
Nannocharax procatopus is assessed by the IUCN Red List as Least Concern, consistent with a wide distribution across multiple river systems in the middle Congo basin spanning Cameroon, Angola and the Democratic Republic of the Congo. No specific population threats are flagged in the sources reviewed here.
As with many small, non-commercial Congo basin characins, this species is not a significant target of the aquarium trade or commercial fisheries, and its conservation outlook is tied more broadly to the health of the Congo basin's river systems — habitat degradation, deforestation and water-quality pressures affecting the wider region — than to any species-specific threat.