Taxonomy & naming
Aphyosemion cinnamomeum was formally described by Henning Svane Clausen in 1963. The type locality is a small rainforest stream approximately 44 miles (43 mi) north of Kumba, in the Mungo River basin of western Cameroon, at approximately 5°14′N, 9°24′E. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) treats cinnamomeum as a valid species within Aphyosemion. The species has at various times appeared in the hobby literature under the synonym or close association with Aphyosemion celiae, and killifish studbooks and the AKA/WAK reference library cross-reference the 'K1/K2' strains with cinnamomeum, reflecting some historical ambiguity in the identity of Cameroonian Aphyosemion material. The genus Aphyosemion is placed in the family Nothobranchiidae by modern molecular phylogenies, though older literature and some current hobbyist sources still use the broader Aplocheilidae arrangement.
The specific epithet cinnamomeum is a Latinised form of the Greek kinnámōmon (cinnamon), describing the warm brown-red colouration of the male body — a straightforward descriptive epithet typical of Clausen's naming practice for West African killifishes. The genus name Aphyosemion derives from the Greek aphyē (small fish) and sēmeion (mark or sign), a reference to the often elaborate markings characteristic of the group.
Morphology
Aphyosemion cinnamomeum is a slender, laterally compressed killifish reaching approximately 2.5 in total length (FishBase) or 2.5 in standard length, placing it at the larger end of the small Aphyosemion species. The body form is typical of the genus: a slightly arched dorsal profile, a rounded or slightly pointed snout, a superior mouth angled for surface feeding, and a rounded to slightly lyrate caudal fin.
Males display the warmer, more elaborately patterned colouration that characterises the group. The body base is a warm ochre to cinnamon-brown, overlaid with rows of red to brick-red spots or dashes along the flanks — the pattern that gives the species its name. The unpaired fins are typically edged with blue-green or yellow margins, and the caudal fin may carry extensions at the upper and lower lobes. Females are smaller and more cryptically coloured, lacking the vivid fin patterning of males and showing a plainer brownish body with reduced or absent red speckling — the strongly sexually dimorphic colouration pattern typical of Aphyosemion.
Habitat
The cinnamon killifish is restricted to the upper Mungo River drainage in western Cameroon, a system draining the volcanic highlands and lowland rainforest of the region between the towns of Kumba and Nkongsamba. The type locality is described as a small stream in rainforest, and the species is understood to inhabit shaded forest brooks and stream margins with overhanging vegetation, leaf litter, and tangled root masses.
Water chemistry in these West African forest streams is typically very soft and slightly to moderately acidic. The AKA/WAK reference library records pH 6.2–7.6 for the species (a broader span than is encountered at any single collecting site, reflecting the range of hobbyist-maintained strains rather than a single locality chemistry), hardness 0–7 dH, and temperatures of 75–79 °F. FishBase notes a nominal temperature of 72 °F for the species and a hardness of 0, consistent with very soft, tannin-stained forest water. These are not seasonal pools but permanent or near-permanent forest watercourses — a key fact that explains the species' non-annual reproductive strategy.
Feeding
Like the great majority of Aphyosemion species, A. cinnamomeum is an opportunistic micro-predator in the wild, taking small invertebrates — aquatic insects and their larvae, microcrustaceans, worms, and similar items — from the water column and the surface film. The superior mouth position is well-adapted to intercepting insects that fall or rest on the water surface in shaded forest streams.
In the aquarium the species accepts a wide variety of small live and frozen foods: Daphnia, Artemia (brine shrimp), bloodworm (chironomid larvae), tubifex, and similar items. Dry foods are often accepted by acclimatised specimens, though condition is generally best maintained with a diet that includes significant live or frozen components. As with most killifishes, overfeeding and poor water quality from uneaten food are greater risks than reluctance to feed.
Mating
Aphyosemion cinnamomeum is a non-annual, plant-spawning killifish — it inhabits permanent forest streams and its reproductive mode is entirely distinct from the peat-burying annual strategy of savanna and seasonal-pool species. Males court females with lateral displays, spreading the fins to show their full colour and pattern. Spawning occurs in pairs: the male aligns alongside or beneath the female and the two press together briefly while a single egg is fertilised and deposited on fine-leaved vegetation, a moss clump, or the fibres of a spawning mop near the substrate or mid-water level.
Spawning is a continuous, low-rate process rather than a single mass-release event. A pair in good condition may deposit a small number of eggs each day over an extended period. The eggs are adhesive and semi-transparent, attached to the spawning medium by a short filament. Males may become aggressive toward females if kept in cramped conditions or if a single male is given no other target; providing two females per male is standard hobbyist practice. The AKA/WAK reference library notes that eggs can be incubated at a ratio of approximately 3:1 (water:egg volume in small containers), reflecting the peat-free water-incubation approach standard for non-annual Aphyosemion.
Breeding
Eggs of A. cinnamomeum are incubated in water rather than stored dry in peat moss — the defining difference from annual killifish care. The AKA/WAK reference records an incubation period of 12–22 days depending on temperature, with warmer water accelerating development. Eggs are collected periodically from the spawning mop or plant clumps and transferred to shallow containers or small jars of aged water for hatching. Fungused eggs should be removed promptly to prevent spread.
Fry are relatively large at hatching by Aphyosemion standards and are able to take freshly hatched Artemia nauplii or microworm immediately — a significant advantage over the smallest killifish species. Growth is moderate; the AKA/WAK reference notes that 5–6 months are required to reach sexual maturity. Separating fry by size as they grow prevents cannibalism. Water quality for fry is critical: small, frequent partial water changes with aged, dechlorinated water of similar chemistry maintain health and growth rate. The BKA/KCF forum archives record historical breeding reports consistent with the plant-spawner approach described here.
In the aquarium
The cinnamon killifish is considered a relatively straightforward species for the killifish hobby, described in the AKA/WAK reference as fairly easy to keep and breed. A pair or trio (one male, two females) can be maintained in a small, well-planted aquarium of 10–15 US gal, with a tight-fitting lid essential to prevent the jumping typical of killifishes. Dense plantings of fine-leaved species (Java moss, hornwort, floating plants) provide cover, reduce male aggression, and serve as natural spawning sites.
Water conditions should approximate the soft, slightly acidic parameters of the native forest streams: pH around 6.2–7.0, hardness below 7 dH, and temperature 72–79 °F. The species does not require extreme blackwater conditions but benefits from peat filtration or the addition of leaf litter to soften and acidify the water gently. Lighting should be subdued; bright lighting stresses the fish and reduces colour expression. Tankmates, if used at all, should be small and peaceful — other small West African killifishes or dwarf Corydoras are the most compatible choices. Larger or more boisterous fish will outcompete and stress this species.
As an Endangered endemic with a restricted wild range, aquarium-maintained populations carry genuine conservation value. Studbook programmes and specialist killifish societies (the AKA in North America, the BKA in the UK) maintain strains and can provide source fish for hobbyists interested in the species — obtaining fish through these networks rather than wild-caught imports reduces pressure on the natural population.
Conservation
The IUCN Red List assesses Aphyosemion cinnamomeum as Endangered (EN), a status that reflects both its genuinely restricted range and the ongoing degradation of the rainforest habitat it depends upon. The species is known from the upper Mungo River drainage of western Cameroon — a geographically small area in which agricultural expansion, small-scale logging, and forest clearance for subsistence farming have reduced and fragmented the shaded forest streams that provide the cool, soft, tannin-stained water these fish require.
The IUCN taxon record carries the identifier 61374 on the Red List. Unlike many killifish threatened by seasonal-pool drainage or spring pumping, the cinnamon killifish faces the slower but equally effective pressure of forest loss — loss of canopy reduces shading, raises water temperatures, alters hydrology, and allows erosion to silt over the stream substrates. Western Cameroon (the Cross–Sanaga–Bioko Forest ecoregion) is recognised as a globally significant biodiversity hotspot and a centre of endemism for freshwater fishes, but forest protection in the region is limited and enforcement is inconsistent.
The species is present in the killifish hobby and is maintained in hobbyist collections in Europe and North America, providing a buffer against wild-population decline. Coordination through specialist societies to maintain genetically diverse captive populations and limit collection pressure on wild fish is the principal current conservation measure available outside of in-country habitat protection.