Taxonomy & naming
Aphyosemion erythron was described by Sonnenberg in 2007. It belongs to the large and species-rich genus Aphyosemion, the most diverse assemblage of African killifishes, placed within the family Nothobranchiidae. The Catalog of Fishes (Eschmeyer, Fricke & van der Laan) records Sonnenberg, 2007 as the valid authority for this name.
The specific epithet erythron is derived from the Greek erythros, meaning red, a direct reference to the regular rows of red dots that decorate the flanks and the red dotting of the fins — features that, together with the species' small size, make it readily identifiable in the hand. The name Chromaphyosemion erytheron is treated as a synonym of this species in Eschmeyer's Catalog of Fishes.
Morphology
Aphyosemion erythron is a slender, laterally compressed killifish with a maximum recorded standard length of 1 in (FishBase), making it one of the smaller members of its genus. The colour pattern is the defining feature: a pale to yellowish or greenish base on the flank is overlaid with regular rows of red or red-orange dots, and the unpaired fins carry red dotting as well.
Sexual dimorphism is typical for the genus. Males are more vividly patterned, with brighter red markings and more elaborate finnage. Females are plainer, generally brownish to olive, with reduced or absent red dots on the fins, and display a rounder abdomen when gravid. The modest size and relatively subtle body depth are consistent with a life spent among dense riparian vegetation and leaf litter in shaded forest streams.
Habitat
The species is endemic to southwestern Equatorial Guinea, with confirmed records from the Río Muni, Río Aye, Río Ecucu, and the lower Río Benito drainage systems. These are tropical, lowland, permanent-water habitats — forest streams and small rivers that retain flow year-round, distinguishing the species from seasonal-pool annual killifishes.
Water chemistry in these West African coastal forest streams is characteristically soft and acidic, often tannin-stained from decaying leaf litter. Seriously Fish records a preferred pH of around 6, a temperature of approximately 72 °F, and a hardness of about 5 dGH — conditions representative of the soft, slightly acidic blackwater and clearwater streams typical of the Guinea–Congolian rainforest belt.
Feeding
Like most Aphyosemion species, A. erythron is an opportunistic predator of small invertebrates in the wild, taking micro-crustaceans, insect larvae, small worms, and other zooplankton encountered at or near the water surface and among submerged vegetation.
In the aquarium the species accepts a range of small live and frozen foods readily — Daphnia, Artemia nauplii, bloodworm, and tubifex are all suitable. Dried foods of appropriate size may also be taken, though live and frozen foods are recommended to maintain condition and colouration, particularly in males preparing for spawning.
Mating
Aphyosemion erythron is a non-annual plant-spawner. It does not bury eggs in substrate or undergo diapause; instead, pairs court and spawn repeatedly over extended periods, depositing individual adhesive eggs among fine-leaved plants, moss, roots, or floating spawning mops near the surface or mid-water. This mode is characteristic of Aphyosemion inhabiting permanent water bodies rather than ephemeral seasonal pools.
Courtship involves the male displaying to the female with spread fins, intensifying his colour, and manoeuvring alongside her. When the female is receptive, the pair press together briefly and release a single egg, fertilised externally. The process is repeated over days or weeks, with a well-conditioned pair producing a steady trickle of eggs rather than a single mass-spawning event.
Breeding
Eggs are small, adhesive, and spherical, and are deposited singly into plant material or mop fibres where they incubate in water at ambient temperature — no drying-out period or diapause is involved, in contrast to annual killifish. At around 72 °F, incubation typically takes two to three weeks, after which the fry are free-swimming and large enough to take newly hatched brine shrimp nauplii or micro-worm as a first food.
The recommended approach in the aquarium hobby is to spawn the pair over a floating mop or Java moss, remove the mop every week or two, and incubate eggs in a small container of soft, slightly acidic water at the parent temperature. Parents may consume eggs given the opportunity, so regular collection is advisable. Fry growth is relatively quick and the fish reach sexual maturity in a few months under good conditions.
In the aquarium
Aphyosemion erythron is best housed in a small, well-planted aquarium with soft, slightly acidic water matching its native chemistry — pH around 6, temperature 68–75 °F, and hardness below 10 dGH. A dark substrate and background, along with floating or fine-leaved plants, bring out the best colour in males and reduce stress for both sexes. A secure lid is essential, as Aphyosemion are capable jumpers.
The species is peaceful and can be kept with other small, non-aggressive fish that tolerate similar water conditions, but is most satisfactorily maintained in a species-only or Aphyosemion-focused setup. Keeping one male with two or more females distributes male attention and reduces harassment of individual females. Water quality should be stable; small, regular water changes with properly conditioned soft water maintain health and encourage spawning. The species is primarily of interest to specialist killifish keepers and members of the killifish hobby community.
Conservation
Aphyosemion erythron has not been formally assessed by the IUCN Red List; its conservation status is recorded as Not Evaluated (NE) on FishBase and hobbyist databases. Its known range is restricted to a handful of river drainages in southwestern Equatorial Guinea — a small, single-country endemic with limited distributional security.
Equatorial Guinea's coastal rainforest zone faces ongoing pressure from logging, agricultural expansion, and oil development. Permanent forest streams of the kind that A. erythron inhabits are vulnerable to siltation, riparian clearance, and altered hydrology from catchment disturbance. As a small, geographically restricted endemic dependent on clean, soft-water forest streams, the species would likely qualify for a threatened or near-threatened designation if formally assessed. Aquarium breeding populations exist within the specialist killifish hobby and provide some ex-situ representation, though no captive programme is coordinated at conservation scale.