Taxonomy & naming
Aphyosemion cyanostictum was formally described by Jean-Louis Lambert and Jacques Géry in 1968 on the basis of material collected from the Ivindo drainage in northern Gabon. The valid name is governed by Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong), which places it within Aphyosemion — the largest and most species-rich killifish genus of sub-Saharan Africa, currently running to well over 100 species across West and Central Africa.
The specific epithet cyanostictum is a compound of two Greek roots: kyanos, meaning dark blue or dark-sea blue, and stiktos, meaning spotted or dotted. Together they describe the male's most conspicuous feature: the dense field of brilliant blue-green spots that covers the flanks and unpaired fins. The name is therefore both literal and appropriate — an unusually direct piece of Linnaean naming for a genus whose epithets are otherwise a mix of Latin colour words, geographical references, and dedicatees.
Within the genus, A. cyanostictum sits in the broadly defined 'Cameroon-to-Gabon' clade of Aphyosemion, a species-rich assemblage of non-annual killifish centred on the rainforest basins of Cameroon, Equatorial Guinea, Gabon, and Congo. Population-level differentiation is well recognised by killi hobbyists: aquarium strains carry collection codes such as LEC 93-5 and LEC 93-59 (the LEC prefix indicating the Léon E. Coucke Belgian collection expeditions of 1993), and these codes are tracked carefully by specialist breeders to preserve genetic identity and avoid inadvertent hybridisation between geographically distinct populations.
Morphology
Aphyosemion cyanostictum is a slender, slightly laterally compressed killifish reaching a maximum recorded total length of 2.5 in in males (FishBase); the common length is closer to 1.5 in TL, and females are notably smaller and less elongate. The body form is typical of the non-annual Aphyosemion — attenuated at the caudal peduncle, the dorsal and anal fins positioned posteriorly and broadly overlapping, producing the classic killi silhouette of a fish that seems to be all fin and tail.
Sexual dichromatism is vivid. Males are the showpiece of the species: the base colour is a warm reddish-brown to olive, overlaid with the close-set blue to turquoise spots that give the species its name. The dorsal, anal, and caudal fins are elaborately patterned, typically showing red or orange banding and edge markings against a blue or yellow-green field; fin rays may extend into filaments in mature males. Females are considerably more subdued — the body is a plain brownish or olive with scattered, faint spots, and the fins carry minimal colour; their bodies are also deeper-bellied, particularly when gravid, and the fins are rounded and short compared to the male's extended rays.
The caudal fin of the male may be rounded to weakly lyrate depending on individual genetics and collection locality, and fin shape is one of the markers hobbyists use alongside collection codes to track population identity across generations in captivity.
Habitat
The species is restricted to a narrow geographic band within the Ivindo river drainage system, between the towns of Ovan and Bélinga in northern Gabon, with records also from adjacent parts of the Republic of the Congo. The Ivindo is one of the major right-bank tributaries of the Ogooué — a large blackwater-influenced river that drains much of Gabon's interior — and the streams A. cyanostictum occupies are small, mostly swampy brooks embedded within closed-canopy lowland rainforest.
These forest brooks are defined by minimal direct sunlight, dense overhanging and submerged vegetation, a substrate of leaf litter and root tangles, and water that is extremely soft and acidic. FishBase records a pH range of 5.5–6.5 and hardness up to 12 dH; the aquarium literature (Aquadiction) concurs with GH 2–12 and pH 5.5–6.5. Water temperature at collection sites is typically in the range of 68–73 °F, though FishBase lists the species' thermal tolerance as extending to 95 °F — likely reflecting the upper bound of survival in stagnant, seasonally warmed water pockets rather than the preferred temperature of shaded rainforest streams.
Because the Ivindo drainage is fed by permanent rainfall within the Congo Basin's wet-forest belt, these streams are non-seasonal; they do not dry out annually. This permanence is the ecological basis for the species' non-annual life history: it does not need to complete its lifecycle before its water body evaporates, and adults can live for two to three years in captivity.
Feeding
Aphyosemion cyanostictum is an omnivore in the broad sense that defines most small killifish: it takes whatever invertebrate prey is available at its scale — small aquatic insects, insect larvae, microcrustaceans, and zooplankton — supplemented by incidental plant matter and organic detritus in the forest-floor streams it inhabits.
In the aquarium the species accepts dried foods, though dietary variety is important to maintaining colour and conditioning fish for breeding. Aquadiction lists bloodworms, daphnia, and tubifex as suitable live and frozen staples. Small, frequent feedings reflect the feeding ecology of a forest-brook predator hunting micro-prey; large or infrequent meals are less appropriate for a fish of this size and disposition. Live Drosophila can be a useful conditioning food for a species that, like many Aphyosemion, readily takes surface-available prey.
Mating
Aphyosemion cyanostictum is a non-annual killifish and a plant and mop spawner — a fundamental point that separates it from the seasonal, peat-spawning annual killies that are often the public face of the family. Because its home streams persist year-round, the species has no evolutionary pressure to pack its entire lifecycle into a race against desiccation; instead, it spawns continuously over extended periods, depositing adhesive eggs individually on fine-leaved plants, moss, roots, or the fibres of an artificial spawning mop.
Male courtship in Aphyosemion is an elaborate visual display: the male fans his fins to their full extent — maximising the spectacle of his blue spots and coloured fin margins — and pursues the female through vegetation, nudging and orienting beside her. Spawning occurs in brief, repeated pairings, with the pair pressing together near the substrate or among vegetation and releasing a single egg at a time, held by a sticky thread to the spawning medium. The male is described by killi hobbyists as shy and slow to mature, and breeding groups of one male to two or three females are recommended to reduce pressure on the female while keeping the male engaged.
The eggs are incubated in water — they receive no parental attention after laying, and neither parent broods or guards. Egg development proceeds at ambient temperature over a period of weeks, without the diapause or delayed hatching that characterises annual species.
Breeding
Breeding A. cyanostictum requires the aquarist to replicate the chemistry of its narrow native habitat: the water must be very soft (GH 2–6 is ideal) and acidic (pH 5.5–6.5), and temperature should be kept at the cooler end of its range, around 68–73 °F. Hard or alkaline water suppresses spawning and increases mortality of both eggs and fry, and many failed attempts in captivity trace back to inappropriate chemistry rather than behavioural problems.
Spawning mops of dark wool or Java moss clumps are the practical spawning media of choice. Eggs are collected by removing the mop and either incubating eggs in a shallow tray of soft, slightly acidic water at the same temperature, or leaving them on the mop in a separate container. Eggs can take three to four weeks to hatch. Fry survival is reported as poor without careful management: the Killi.co.uk specialist database notes that fry need protection and that moss provides useful cover. Initial foods are infusoria or commercial fry powder, graduating to freshly hatched brine shrimp nauplii as the fry grow. Adults live up to approximately three years in captivity (Aquadiction), giving the keeper a comparatively long window to work with established breeders.
Aquadiction records egg production of 20–50 eggs per day over several weeks — a substantial total output for a fish of this size — though the combination of poor fry survival and demanding water requirements places the species firmly in the specialist rather than the general hobbyist category.
In the aquarium
Aphyosemion cyanostictum is classed as a difficult aquarium species (Killi.co.uk), and that rating is earned. The primary constraint is water chemistry: it will not thrive, let alone spawn, in the hard or moderately hard tapwater that is the baseline in most parts of Europe and North America. Successful keepers work with RO water remineralised to very low hardness, or with naturally soft source water, and manage pH carefully in the lower-acidic range. A tight-fitting lid is essential — like all killifish, it is an accomplished jumper.
The species is peaceful and diminutive, and must not be housed with fish large enough to prey on it. A well-planted species tank with soft lighting, a dark substrate, and floating or fine-leaved plants that recreate the visual environment of its forest-brook home is both functionally appropriate and aesthetically fitting: the male's colours are most fully expressed under subdued, diffused light against a dark background, where the blue spots and fin markings appear to glow. Small groups — one male to two or three females — are the standard recommendation, with cover available for subordinate females.
FishBase notes the species as 'very difficult to maintain in the aquarium', a characterisation that has kept it largely a specialist fish despite its extraordinary colour. For a killi enthusiast equipped to provide the right conditions, however, it represents one of the more rewarding small African species in the genus: long-lived compared to the annuals, active and displayable, and available in documented collection-locality strains from the major killi clubs and hobbyist networks.
Conservation
The IUCN Red List assessed Aphyosemion cyanostictum as Least Concern (LC) in February 2009, the assessment recorded in both the IUCN database and cross-referenced in FishBase (Ref. 130435, Version 2025-2). The LC rating reflects the species' range within a region of Gabon that remains substantially forested — the Ivindo drainage, including the area around Bélinga, retains extensive closed-canopy rainforest cover, and logging pressure in much of northern Gabon's interior has historically been lighter than in West Africa's more accessible coastal forests.
Nonetheless, A. cyanostictum's restricted range within a single drainage system — confined to the relatively narrow corridor between Ovan and Bélinga — means it has little buffer against habitat deterioration. Mining activity in the Bélinga area (centred on iron ore deposits) has been a source of concern for conservationists in Gabon since the 2000s, with potential for road-building, stream sedimentation, and runoff to affect the soft-bottomed, chemistry-sensitive streams the species occupies. Deforestation and changes to the hydrology of small rainforest streams are the proximate threats most likely to affect a forest killifish of this type.
The aquarium hobby maintains viable captive populations of the documented collection strains (LEC 93-5, LEC 93-59), and the killifish specialist community's culture of strain-coded breeding and exchange provides a degree of ex-situ insurance — though the long-term value of that insurance depends on hobbyist populations remaining genetically managed rather than mixed.