Taxonomy & naming
Aphyosemion zygaima was described by Jörg-Volker Huber in 1981. Eschmeyer's Catalog of Fishes (CAS) treats Huber, 1981 as the valid authority for the species, placing it in the large genus Aphyosemion within the family Nothobranchiidae — the African rivulines. The parenthetical or non-parenthetical presentation of the authority follows the original combination; the name has not been moved to another genus since its description.
Within Aphyosemion the species belongs to the diverse assemblage of West and Central African forest and savanna killifishes, a group whose internal classification has been revised repeatedly as molecular phylogenetics has resolved relationships among the roughly 80–90 described species in the genus. The specific epithet zygaima has not been widely parsed in the available literature; its derivation remains unclear from current secondary sources, and no confident etymology is presented here.
Morphology
FishBase records a maximum total length of 2 in for Aphyosemion zygaima, placing it in the small-to-medium size range typical of the genus. Like most Aphyosemion, the body is moderately elongate and laterally compressed, tapering to a rounded or slightly pointed caudal fin. Males of killifishes in this genus typically carry more vivid colouration than females, often displaying iridescent blue, green, or red patterning on the flanks and fins; females are generally more cryptic, with a plainer olive-brown or tan ground colour.
Specific colour pattern data for A. zygaima from the literature are sparse in the secondary sources available, and a detailed description of fin-ray counts, squamation, and sexually dimorphic markings awaits a formal morphological review of material from the type locality.
Habitat
The only documented locality for Aphyosemion zygaima is a savanna brook near Midouli in southern Congo (Republic of Congo). This stream drains savanna country — open grassland or woodland rather than closed-canopy rainforest — and FishBase records the species as inhabiting permanent water, distinguishing it from annual Aphyosemion congeners that live in seasonally drying pools.
Savanna streams in this part of Central Africa are typically shallow, clear to lightly tannin-stained, slow-flowing or still, and underlain by sand or leaf litter. Water chemistry in such systems tends toward soft and mildly acidic conditions. General data for plant-spawning Aphyosemion in the West–Central African region suggest temperatures of roughly 68–81 °F and general hardness in the range of 80–200 ppm; site-specific measurements for the Midouli brook are not recorded in the available sources.
Feeding
Aphyosemion zygaima is presumed to be a small invertebrate predator in the wild, consistent with feeding behaviour documented across Aphyosemion. In their natural savanna-stream habitat, members of the genus take aquatic and terrestrial insects, small crustaceans, worms, and zooplankton at and near the water surface and in the mid-water column.
In captivity, hobbyists familiar with the genus report that small live or frozen foods — daphnia, artemia nauplii, bloodworm (chironomid larvae), and micro-worms — are accepted readily. Dry foods can be offered as a supplement but should not form the bulk of the diet for a fish adapted to a protein-rich live-prey diet in the wild.
Mating
Aphyosemion zygaima is a non-annual killifish and a plant-spawner. Males court females with lateral displays, spreading their fins to present the full extent of their colouration. Unlike the dramatic leap-and-dive spawning posture of annual soil-burying killies, plant-spawning Aphyosemion pairs assume a side-by-side position among fine-leaved aquatic vegetation, roots, or fibrous spawning mops, depositing a small number of adhesive eggs at each spawning event over an extended period of days or weeks.
The eggs adhere to the plant material or mop fibres and are left in place, unguarded. The pair do not form a prolonged bond; the male may court and spawn with multiple females. This mode of reproduction — continuous low-fecundity spawning across permanent water — is the biological opposite of the high-fecundity burst spawning and obligate diapause of annual species.
Breeding
Hobbyists keeping Aphyosemion zygaima under the collection code CMBB 89-01 report that the species can be bred successfully given appropriate environmental conditions, and that it is 'easy to breed' once those conditions are met. Eggs are deposited adhesively on fine-leaved plants or synthetic spawning mops and incubate in water with no diapause requirement — the embryos develop continuously in the aquatic environment over a period of roughly two to three weeks depending on temperature.
Fry are comparatively large at hatching relative to annual killifish larvae and can take baby brine shrimp nauplii or micro-worms from the first day of free-swimming. Because the adults are continuous spawners over weeks, eggs at different stages of development may be present simultaneously; breeders typically check spawning mops every few days to collect and separately incubate eggs, protecting them from adult predation. Water for incubation and fry-rearing should be soft and slightly acidic, kept clean by small regular water changes.
In the aquarium
Aphyosemion zygaima is a specialist's fish — uncommon in the hobby and available almost exclusively through killifish society networks and dedicated breeders rather than the general trade. The CMBB 89-01 collection strain is the reference line circulating among enthusiasts. Its small size (to 2 in TL) makes it suitable for a modestly sized aquarium of 10–15 US gal, decorated with fine-leaved plants, floating vegetation, and driftwood or botanicals to provide the tannin-stained, low-light conditions it prefers.
Water should be soft and slightly acidic — consistent with the general Aphyosemion plant-spawner parameters of 68–81 °F and 80–200 ppm general hardness. The species is reported as 'difficult to maintain' by FishBase, suggesting it may be sensitive to water quality lapses or to water that is too hard or alkaline. A well-established, stable aquarium with gentle filtration and regular small water changes is advisable. Males may spar but serious injury is uncommon in an adequately planted tank; a ratio of one male to two or more females reduces inter-male aggression.
Conservation
The IUCN Red List assessed Aphyosemion zygaima as Data Deficient (DD) in 2009, a status that reflects the absence of meaningful population data rather than a documented stable population. The species is known from a single locality — a savanna brook near Midouli in southern Congo — and has apparently not been recollected or surveyed systematically since the original description. A species with a range this restricted is inherently vulnerable: any single localised threat (stream diversion, agricultural run-off, drought intensification under climate change, or the introduction of mosquitofish Gambusia or other exotic species) could extirpate the entire known population.
The savanna streams of southern Congo have not been the subject of comprehensive conservation planning for killifishes. Continued habitat degradation from expanding agriculture and land clearance in the region represents a plausible background threat. Until targeted surveys confirm the survival and extent of the Midouli population, the DD listing offers no real conservation guidance. Killifish societies maintain captive populations under collection codes such as CMBB 89-01, providing insurance against wild extinction — a conservation role that is particularly significant for single-locality endemic species such as this one.