Taxonomy & naming
Microctenopoma nanum was originally described by Albert Günther in 1896 as a member of the genus Ctenopoma, the broad catch-all for African anabantoids then in use. The species was later reassigned to Microctenopoma Norris & Teugels, 1990, a genus erected to accommodate the smaller, more slender West and Central African bushfishes that differ from the larger Ctenopoma in proportions, squamation, and reproductive behaviour. Eschmeyer's Catalog of Fishes (CAS) records the current valid name as Microctenopoma nanum (Günther, 1896), with the parenthetical authority reflecting the generic transfer from Ctenopoma.
The species belongs to the family Anabantidae — the climbing perches and true bushfishes — whose members all possess the labyrinth organ, a folded suprabranchial chamber that allows the fish to extract oxygen directly from atmospheric air. Within Microctenopoma, M. nanum is distinguished from congeners by a combination of characters: a narrow interorbital width, distinct and even vertical bars on the flanks that persist at all body sizes, serration of the subopercle in adult individuals, a squared-off caudal fin, and the absence of orange colouration on breeding males — a reliable field mark separating it from related species that flush orange during courtship.
Morphology
Microctenopoma nanum is a small, moderately elongate anabantoid reaching approximately 2.5 in standard length, with occasional individuals reported to 3 in. The body is somewhat laterally compressed and fusiform, bearing the ctenoid (rough-edged) scales that give the genus its name — Microctenopoma meaning 'small comb-cover,' referring to the serrated opercle. The dorsal fin carries 13–18 spines and the anal fin 6–10 spines; both are relatively long-based, and the caudal fin is distinctly squared rather than rounded or forked.
The colour pattern is the species' most useful identification feature: a series of vertical dark bars of roughly even width and spacing runs along the flank against a brownish or olive-grey background, and these bars remain visible at all life stages rather than fading as the fish matures. Males are somewhat larger and more intensely coloured than females, with colours brightening during spawning activity, though they do not develop the orange flush seen in some congeners. The suprabranchial labyrinth organ is visible anatomically as an elaborately folded accessory respiratory structure that gives the fish a slightly raised profile just behind the head.
Habitat
Microctenopoma nanum occupies freshwater habitats across a broad swath of Central and West Africa, recorded from the Congo River basin in the Central African Republic, Republic of Congo, and Democratic Republic of the Congo, and along the Lower Guinea coastline from the Sanaga River drainage in Cameroon south to the Chiloango River system near the Angola–DRC border. This range encompasses some of the largest river systems in Africa and a diversity of hydrological settings.
Within this range the species is typically found in slow-flowing or still marginal habitats: quiet backwaters, flooded vegetation, heavily overgrown stream banks, and swampy forest margins where dissolved oxygen is naturally low and surface access for aerial respiration is unimpeded. Water temperatures in these equatorial lowland systems typically fall between 17 and 75 °F, with soft to moderately hard, slightly acidic to neutral water — pH 6.0–7.5 and general hardness up to about 15 dH. Dense aquatic and emergent vegetation is a consistent habitat feature; the species is benthopelagic, spending time both near the bottom and in the water column among plant stems.
Feeding
Microctenopoma nanum is a carnivore in the wild, taking small aquatic invertebrates — insect larvae, small crustaceans, worms, and similar prey — that it locates among vegetation and near the substrate. Like other anabantoids it is a visual predator that hunts by sight in the upper reaches of the water column and amid plant cover.
In captivity the species has a preference for live and frozen foods and may initially ignore or refuse dry foods entirely. Bloodworms, mosquito larvae, daphnia, and brine shrimp are reliable staples; some individuals can be gradually conditioned to accept high-quality micro-pellets, but varied live and frozen offerings produce the best colour, condition, and willingness to spawn. Feeding small quantities twice daily matches the fish's natural foraging pattern and reduces the risk of polluting the calm, low-turnover water it prefers.
Mating
Microctenopoma nanum is a substrate spawner rather than a bubble-nester: courtship and egg deposition take place at or near the substrate or among floating plant material, without the male constructing or tending a foam nest. Spawning typically occurs in the evening, and the act itself is brief. The male courts the female with colour displays and fin spreading, intensifying his barred pattern, then the pair come together over the spawning site for egg deposition.
Sexual dimorphism is modest but present: males are larger and more vividly coloured, and their intensity increases during courtship, whereas females are somewhat plainer and, when ripe, show a fuller abdomen. Unlike some congeners, breeding males of M. nanum do not develop orange colouration — the barred flanks remain the dominant visual signal throughout courtship.
Breeding
Spawning in Microctenopoma nanum takes place in the evening over a substrate or among floating plant material. The eggs are small and buoyant, rising to the surface where they may adhere to floating vegetation; there is little or no parental care reported after egg deposition, which distinguishes this species from congeners that guard eggs in a bubble nest. Eggs hatch in approximately 24 hours under warm conditions, and the fry become free-swimming within a further two to three days.
For the aquarist, a dedicated breeding setup is advisable: a small, heavily planted tank with gentle, minimal filtration, a tight-fitting lid (both to maintain the humid air column the labyrinth organ requires and to prevent the buoyant eggs from being disturbed by surface turbulence), and water in the warmer part of the species' range, around 72–75 °F. After the adults spawn they should be removed or the eggs transferred, as the adults offer no protection and may consume the eggs. First foods for the fry are infusoria and similarly fine fare in the first week, followed by microworms and newly hatched brine shrimp as the fry grow. Sexual maturity is reached at roughly two years of age; the species can live up to five years under good conditions.
In the aquarium
Microctenopoma nanum is a rewarding but somewhat specialised aquarium subject. It is peaceful and can be kept with other small, non-aggressive species — fine-bodied tetras, small rasboras, corydoras, and similar calm tankmates — but its preference for live food and still or very gently moving water means it is less suited to a busy community tank than hardier species. A tank of 23.5–31.5 in in length with dense planting, floating plants to diffuse light and provide surface cover, and a gentle sponge filter is close to ideal.
Water should be soft to moderately hard (GH 5–15) and slightly acidic to neutral (pH 6.0–7.5), with temperatures in the 63–75 °F range — the species tolerates the cooler end of this range well, which sets it apart from strictly tropical gouramis. Because it is a labyrinth fish, the space between the water surface and the tank lid must be kept warm and humid; a cold draught onto the labyrinth organ can cause respiratory damage. The species is not strongly territorial but pairs or small groups are best, as single individuals may become shy. Its tendency to ignore dry foods means the keeper should plan on maintaining live or frozen food cultures. Lifespan with good care is up to five years.
Conservation
Microctenopoma nanum is assessed as Least Concern (LC) on the IUCN Red List, an assessment reflecting its broad natural range across the Congo basin and Lower Guinea coastal drainages rather than any inherent resilience to habitat change. A wide geographic distribution across multiple large river systems reduces the risk of range-wide decline from localised pressures, and no major population-level threats have been identified in the available literature.
Nonetheless, Congo basin freshwater habitats face growing pressures from deforestation, small-scale agriculture expanding into riparian zones, and artisanal and industrial extraction activities that affect water quality and flow regimes across the region. As a small anabantoid that relies on calm, well-vegetated marginal habitats, M. nanum could be locally affected by vegetation removal and water-body modification even where the species is not formally considered at risk. The aquarium trade does harvest small numbers from the wild, but tank-bred individuals are available and represent the preferred source for aquarists. The LC assessment was last reviewed in 2009.