Taxonomy & naming
Ctenopoma nebulosum was described by J.S. Norris and G.G. Teugels in 1990. Eschmeyer's Catalog of Fishes records the valid name as Ctenopoma nebulosum Norris & Teugels, 1990. The species belongs to the genus Ctenopoma Peters, 1844 — the African climbing perches or African bushfishes — a group of labyrinth fishes (family Anabantidae) distributed across sub-Saharan Africa. Norris subsequently treated the West African anabantids in his 2003 contribution to Faune des poissons d'eaux douces et saumâtres de l'Afrique de l'Ouest, which remains the primary regional reference for the species.
The specific epithet nebulosum derives from the Latin nebulosus, meaning cloudy, misty, or mottled — a direct reference to the species' mottled, dark-brown flanking pattern. The genus name Ctenopoma combines the Greek ktenos (comb) and poma (lid or cover), alluding to the serrated or toothed margin of the preoperculum that characterises the group. Within Ctenopoma, the genus has historically been divided informally into species groups based on body shape, squamation, and dentition; C. nebulosum belongs to the West African assemblage rather than the more diverse Central African radiation.
Morphology
Ctenopoma nebulosum is a moderately sized anabantid, with FishBase recording a maximum standard length of approximately 4 in in males and 3.5 in in females. The body form is typical of the genus: laterally compressed, moderately deep, with a blunt snout and jaws described as weakly protrusible. The overall profile gives the fish a slightly humpbacked silhouette when viewed from the side, and the ctenoid scales across the flanks contribute to the rough, comb-like texture characteristic of the genus.
The coloration is cryptic and mottled: the ground colour is a dark brown to olive-brown, overlaid with irregular darker blotches and cloudy banding on the flanks — the pattern that inspired the species name. A dark caudal spot is present at the base of the tail. The pelvic fins are darkly pigmented. This disruptive pattern serves as camouflage in heavily vegetated, tannic, and turbid river margins. As in other labyrinth fishes, C. nebulosum possesses a suprabranchial organ (labyrinth organ) that allows it to breathe atmospheric oxygen directly, though the organ is described as relatively simple compared to some other anabantids. Sexual dimorphism is modest; males reach a somewhat larger maximum size than females.
Habitat
Ctenopoma nebulosum is endemic to southeast Nigeria. The IUCN assessment places it in the Sombreiro, Isiokpo, Chokoche, Imo, and Kwa Ibo rivers, as well as the New Calabar river system, all within or adjacent to the Niger Delta. FishBase additionally records it from the Lower Cross River. The species occupies freshwater wetlands, including rivers and streams, permanent freshwater pools, and seasonal freshwater marshes — typical of the shallow, heavily vegetated, often turbid habitats that characterise the Niger Delta's freshwater zones.
As a labyrinth fish, C. nebulosum is well suited to warm, low-flow or stagnant water where dissolved oxygen can be low. FishBase records a temperature of 75 °F for the species; the Niger Delta lowland environment is equatorial and warm year-round. The species is described as benthopelagic — associated with the lower and mid-water column near cover — rather than a dedicated open-water swimmer. Dense marginal and aquatic vegetation, submerged root systems, and organic substrate likely provide both shelter and foraging microhabitats. Given the IUCN's reported extent of occurrence (EOO 2,983–12,523 mi²) and extremely restricted area of occupancy (AOO 17 mi²), the species has a very small effective range even within the Niger Delta.
Feeding
No detailed dietary studies of Ctenopoma nebulosum have been published, but its morphology and the feeding ecology of related Ctenopoma species give a reasonable picture. The weakly protrusible jaws and moderately sized mouth are consistent with a generalised ambush or stalking predator of small invertebrates, insect larvae, small crustaceans, and occasionally small fishes. Like many African bushfishes, it likely relies on its cryptic coloration to approach prey rather than active pursuit.
In the aquarium, related Ctenopoma species accept small live and frozen foods — bloodworm, brine shrimp, Daphnia, and similar invertebrate-based foods — and may be persuaded onto quality prepared foods with patience. Small live foods and frozen equivalents typically produce the best results with wild-caught or recently imported specimens.
Mating
Reproductive behaviour in Ctenopoma nebulosum has not been formally documented in the scientific literature. Closely related West African Ctenopoma species are open-water egg-scatterers: the buoyant or semi-buoyant eggs are broadcast into open water with no nest construction and no parental care. This mode — shared with other members of the family Anabantidae — contrasts with the bubble-nest building seen in many Asian labyrinth fishes.
Where Ctenopoma spawning has been observed in captivity (principally in C. acutirostre and other better-known congeners), males display toward females with fin extension and lateral presentation, and spawning occurs in open water with the pair embracing briefly in the manner of anabantids generally, releasing buoyant eggs that rise toward the surface. These eggs float freely and receive no further care from either parent.
Breeding
No captive breeding reports specific to Ctenopoma nebulosum have been published, and the species is rarely encountered in the aquarium trade. Based on the reproductive biology of the genus, eggs would be expected to be buoyant, released in open water, and left to develop unattended. Incubation times at tropical temperatures for related species are typically in the range of one to three days, yielding small, free-swimming fry that initially subsist on yolk.
Given its Endangered status and the pressures on wild populations, captive breeding of this species would carry genuine conservation value, though the scarcity of specimens in the hobby makes this largely theoretical at present. Aquarists fortunate enough to obtain the species should follow general protocols for Ctenopoma: warm, well-filtered but gentle flow, cover-rich aquaria, and conditioning with varied live and frozen foods.
In the aquarium
Ctenopoma nebulosum is extremely rare in the aquarium hobby. It is not regularly exported from Nigeria and has no established captive-bred trade population. The species' Endangered status, restricted range, and the ecological crisis of the Niger Delta make any increase in collection pressure undesirable; aquarists who encounter it should prioritise sourcing any captive-bred specimens that may exist.
For aquarists with access to the species, care would follow the general template for West African Ctenopoma: a species aquarium or a quiet community of similarly sized, non-aggressive fish; plenty of vegetation, driftwood, and cover to satisfy the species' cryptic, sedentary nature; warm, soft-to-moderately-hard water around 75–79 °F; and a diet of small live and frozen invertebrate-based foods. As a labyrinth fish it requires unobstructed access to the water surface to breathe air. Filtration should provide good water quality with gentle flow. The species is unlikely to compete well with bold or aggressive tankmates.
Conservation
Ctenopoma nebulosum is assessed as Endangered (EN) on the IUCN Red List under criteria B1ab(i,ii,iii)+2ab(i,ii,iii), reflecting a small, fragmented, and declining range. The assessment, published in 2020 based on a 2019 evaluation by B.D. Olaosebikan, records an extent of occurrence of 2,983–12,523 mi² and an area of occupancy of just 17 mi², with the species known from only two threat-based locations. This represents a deterioration from its previous 2010 assessment of Vulnerable.
The threats are severe and characteristic of the Niger Delta: wholesale deforestation of riverine buffer zones, oil exploration and extraction with attendant pollution from industrial effluents and spills, and broader ecosystem conversion and degradation across one of the world's most ecologically stressed river deltas. The population trend is unknown. The species is taken for local food consumption and the domestic aquarium trade, though at what level is unquantified. At the time of assessment it occurred in no protected areas and was subject to no active conservation plan. The combination of a tiny effective range, ongoing habitat loss, and institutional gaps in protection makes C. nebulosum one of the more acutely at-risk anabantid fishes in West Africa.