Taxonomy & naming
Aphyosemion poliaki was described by the Swiss-Cameroonian naturalist Jean-Louis Amiet in 1991, based on material collected from streams in the Mount Cameroon region of southwestern Cameroon. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) records the valid combination as Aphyosemion poliaki Amiet, 1991. The species belongs to the large African killifish genus Aphyosemion — the most species-rich genus of aplocheiloid killifishes — and is placed within the subgenus Chromaphyosemion, a clade of non-annual Cameroonian and Gabonese killies characterised by vibrant male coloration and plant-spawning reproductive biology.
The species is named in honour of Daniel Poliak, a French aquarist and killifish hobbyist who contributed to the collection and documentation of West African killifish diversity. The American Killifish Association records that Poliak's killifish has appeared in 24 issues of the Journal of the American Killifish Association, reflecting the sustained hobbyist interest the species has attracted since its description. Killi-Data (Huber, 1996) is cited as a key reference for the species' early documentation in the specialist literature.
Morphology
Aphyosemion poliaki is a slender, slightly laterally compressed killifish reaching approximately 2 in total length (FishBase) to around 2.5 in in the largest individuals. The body plan is typical of Chromaphyosemion: elongate, with a subterminal mouth well adapted to surface and mid-water invertebrate prey, a rounded to slightly pointed snout, and fins that in males extend into ornate, colour-saturated displays.
Sexual dimorphism is pronounced. Males display a base coloration of bright yellow to orange, overlaid with a complex pattern of red spots and streaks, while the dorsal, anal, and caudal fins carry bold markings in combinations of red, blue, and black that vary in detail across the species' different collection localities. Females are far more subdued — light grey-brown overall, with smaller, simpler, largely unpatterned fins — a typical pattern in the genus where the female's cryptic coloration provides camouflage during the extended period she spends near the substrate or among fine plant material depositing eggs.
Habitat
Poliak's killifish is endemic to the streams and small forest watercourses of southwestern Cameroon, principally in the foothills and lower slopes of Mount Cameroon and surrounding areas. Documented collection localities include Monea, Buea, Ekona, Mile 33, Tamben, and Bolifamba — all within the humid forest zone of this volcanic massif — and a single additional locality in Ivory Coast (Côte d'Ivoire) extends the known range marginally westward. With 34 recorded collection points, the species' distribution is better-mapped than many congeners, but remains geographically compact.
The native waters are the soft, mildly acidic to near-neutral streams typical of West African lowland forest: shallow, shaded by dense riparian and forest canopy, stained with tannins and humic acids from decaying leaf litter, and flowing slowly or intermittently over sandy or silty substrates. Water temperature in this equatorial zone falls in the range of 68–75 °F (FishBase), with little seasonal fluctuation. The streams draining Mount Cameroon's heavily watered western slopes receive among the highest rainfall in Africa, sustaining year-round flow that underpins the non-annual reproductive strategy of this species — unlike their dry-savanna relatives, Chromaphyosemion killies do not need to encode a diapause into their eggs because their home waters persist.
Feeding
Like most members of the genus, Aphyosemion poliaki is an omnivore that strongly favours small animal prey. In the wild it forages on aquatic and terrestrial invertebrates — insect larvae, small crustaceans, and zooplankton — taken at or near the water surface and in the water column, consistent with the subterminal mouth and active mid-water hunting posture of Chromaphyosemion species.
In captivity the species does best on a varied diet weighted toward live and frozen meaty foods. Brine shrimp (Artemia), daphnia, bloodworms (Chironomid larvae), and small insect larvae are all accepted and promote good condition, intense male coloration, and regular spawning readiness. A high-quality micro-pellet or granule can supplement the diet but should not dominate it; killies maintained exclusively on dry food frequently show reduced spawning drive and dulled coloration.
Mating
Aphyosemion poliaki is a non-annual killifish and a plant-spawner — its reproductive mode is fundamentally different from the soil-burying annuals of the savanna and Sahel. Rather than depositing desiccation-resistant eggs in substrate that will dry out completely, pairs of A. poliaki spawn continuously over weeks and months, pressing individual adhesive eggs onto fine-leaved plants, moss, floating spawning mops, or fine roots near the surface or mid-water column. There is no diapause requirement; eggs develop directly in water.
Male courtship displays are vigorous and visually striking, with the male erecting and fanning his ornamented fins before the female and manoeuvring her toward the chosen spawning site. A single pair or a group of one male and two females can be maintained in a dedicated breeding setup. Because males will pursue females relentlessly, adequate cover — dense plants or additional females to distribute attention — is important to prevent females being harassed to exhaustion.
Breeding
Eggs are deposited singly or in small batches over an extended period — a typical breeding session runs one to two weeks of daily or near-daily egg-laying. Individual eggs are small, adhesive, and transparent to slightly amber-tinted. At typical aquarium temperatures of 72–79 °F, eggs hatch in approximately 10–20 days when incubated directly in water.
Eggs can be collected by picking them from mops or plants by hand, or by moving the spawning mop itself into a shallow container with clean, slightly acidic soft water. An alternative technique noted in the hobby is brief damp-peat storage of eggs for approximately three weeks followed by re-saturation with soft water to trigger a more synchronised hatch — a technique borrowed from annual-killi practice that can be useful for shipping eggs or building up a cohort of same-age fry. Newly hatched fry are small but capable of accepting microworms and freshly hatched Artemia nauplii from the outset. Adults live up to approximately three years under good aquarium conditions, longer than most annual killies.
In the aquarium
Poliak's killifish is a peaceful, small-bodied species suitable for a nano or species aquarium of 10–15 US gal. It is compatible with other small, non-aggressive fishes in a community setting but is typically best displayed in a species tank or alongside similarly sized, non-competitive companions; the males' elaborate fin displays and coloration are easiest to appreciate without bolder species competing for space or food. FishBase notes the species is considered difficult to maintain, likely reflecting its sensitivity to water quality and its specific chemistry requirements rather than any behavioural complexity.
Water should be soft and slightly acidic to neutral: pH 6.0–7.5, general hardness (GH) 5–15, and temperature 72–79 °F. Regular partial water changes are important — killifishes are sensitive to accumulated nitrates and dissolved organic waste. Dense planting with fine-leaved species (Java moss, Ceratopteris, Taxiphyllum) provides both cover and a natural spawning substrate, and floating plants further diffuse the light to mimic the shaded forest streams of Mount Cameroon. The aquarium must be tightly covered: even non-annual killies are accomplished jumpers.
The species is relatively well established in specialist killifish circles and is periodically available through killifish association auctions and fish-room trades, though it does not appear in the mainstream ornamental trade with any regularity. Keeping and breeding this fish outside its native range carries a modest conservation value for a species under pressure in the wild.
Conservation
The IUCN Red List assessed Aphyosemion poliaki as Endangered (EN) in February 2009, under criteria B1ab(iii)+2ab(iii), meaning the species has a restricted extent of occurrence and area of occupancy, and faces continuing decline in the extent or quality of its habitat. The assessment was conducted by Moelants (2010) and remains the current status under IUCN Red List Version 2025-2.
The primary threat is habitat loss and degradation in the Mount Cameroon region. The lower slopes and foothills of this massif — precisely the zone where most A. poliaki collection localities are concentrated — have experienced sustained forest clearance for agriculture, plantation development (particularly oil palm and rubber), and expanding peri-urban settlement associated with Buea and the coastal economic corridor. Forest streams lose shade, water chemistry shifts toward higher temperatures and pH as riparian vegetation is removed, and siltation from erosion degrades the shallow, clear-bottomed habitats the species requires.
Because the species' entire known range occupies a geographically compact area within a single country, any widespread habitat deterioration affects all known populations simultaneously. The Ivory Coast locality extends the range marginally but does not materially change the vulnerability picture. No targeted conservation measures specific to A. poliaki are recorded; the species' survival is contingent on the broader protection of lowland forest habitat on Mount Cameroon's western face, a landscape that remains under considerable development pressure.