Taxonomy & naming
Fundulosoma thierryi was described by Ernst Ahl in 1924, with the type locality recorded from the Mangu District of northern Togo, specifically the area between the villages of Kadjamba and Bogo-Moba south to Panpamba and Nacjaba. The genus Fundulosoma is monotypic — thierryi is the only valid species it contains — and it sits within the family Nothobranchiidae, the African nothobranchid killifishes that include the diverse annual and non-annual genera of sub-Saharan Africa. Eschmeyer's Catalog of Fishes maintains the valid combination as Fundulosoma thierryi Ahl, 1924.
The species has a somewhat tangled aquarium history that complicates the literature. Hobbyist records document persistent confusion with Fundulopanchax walkeri (formerly placed in Aphyosemion), a West African killifish of superficially similar colouration but different reproductive biology. Multiple aquarium strains are documented — carrying locality codes such as Ghana 94/1, Mali, K'palimé TOGO 1, and Ada GH 06/5 — and the American Killifish Association's library records at least 25 issues of the JAKA journal addressing the species across the period 1969–2015, reflecting its long presence in the hobby and the sustained interest it has attracted from specialists. The name Nothobranchius thierryi is treated as a synonym of this species in Eschmeyer's Catalog of Fishes.
Morphology
Fundulosoma thierryi is a very small fish. FishBase records a maximum total length of 1.5 in, and British Killifish Association notes that males in breeding condition rarely exceed 1.5 in (approximately 1.25 inches). Sexual dimorphism is marked, as is typical in African annual killifishes: males are more intensely coloured, with lateral flanks patterned in blues, reds, and iridescent markings characteristic of the Nothobranchiidae, while females are considerably plainer and often brownish-olive, a cryptic colouration suited to life among leaf litter and aquatic debris at the pool floor.
The body form is compact and fusiform, adapted to life in shallow, still, seasonally variable water. The fins are moderately sized; males display more elongated and ornamented dorsal and caudal fins. Eggs are roughly 0.5 in in diameter, non-adhesive, with few short filaments, and lack the reticulated membrane surface seen in some other nothobranchid species. Males can produce eggs (i.e. become sexually active) from as small as 0.5 in total length — a remarkable precocity consistent with the annual life strategy — but productivity declines sharply after approximately 10–12 weeks of age in captivity.
Habitat
Across its range Fundulosoma thierryi inhabits temporary pools, seasonal swamps, and small semi-permanent standing waters embedded in West African savanna and Sahel-margin landscapes. The pools form with the onset of the rainy season and contract or disappear entirely in the dry season, imposing the annual cycle of filling, reproduction, desiccation, and re-filling that defines the biology of the species.
Water chemistry data from wild collection sites reflects this savanna setting and varies by locality. FishBase records a generalised range of pH 6.5–7.5 and moderately soft to slightly hard water (dH 8–10), at temperatures of 70–72 °F. However, field data from Tano River sites in Ghana collected by Kluge (1959–60) paint a different picture for at least some populations: 73–81 °F, pH 5.7, and German hardness of only 1.5 — very soft, mildly acidic conditions more typical of forested-pool chemistry infiltrating into the savanna zone. This variation across collection sites suggests the species tolerates a modest range of water-quality conditions rather than being strictly tied to neutral, moderately hard water across its full distribution.
Feeding
In natural pools Fundulosoma thierryi feeds opportunistically on the small invertebrates and zooplankton that colonise seasonal West African water bodies: chironomid larvae, copepods, ostracods, small aquatic insects, and similar benthic and water-column invertebrates. The small mouth and body size constrain prey to items well under a centimetre.
In the aquarium the species accepts live and frozen small foods without difficulty. Artemia nauplii and small Daphnia are standard staples, along with micro-worms and finely minced frozen foods. Very small prepared micro-pellets may be taken, but live and frozen invertebrate foods produce the best colouration and reproductive condition in males. Because males are territorial and competitive, ensuring that subordinate individuals receive adequate food during regular feeding is worthwhile.
Mating
Fundulosoma thierryi is an annual killifish that practises substrate-spawning — specifically, peat- or mud-diving, the defining reproductive mode of the African nothobranchid annuals. Males are territorial and competitive; females are not. Courtship involves a male displaying his lateral colour pattern at close range before manoeuvring alongside the female to press her toward the substrate surface. Pairing occurs when both fish dive briefly into the soft sediment, releasing eggs and sperm simultaneously within the substrate matrix.
Spawning occurs in daily bouts when a reproductively active pair is present. Because males become sexually active at very small body sizes — as little as 0.5 in — and because productivity wanes substantially after 10–12 weeks in the wild generation, the species compresses mating effort into a very narrow window. This places a premium on early sexual maturity and high spawning frequency during peak condition, consistent with life in a pool that may persist for only a few months before drying.
Breeding
In the wild, fertilised eggs are left buried in the soft sediment — peat, mud, or fine detritus — as the pool dries around them. The eggs enter diapause, the state of arrested embryonic development that allows nothobranchid annual embryos to survive the dry season in the substrate. When rains return and the pool refills, the eggs hatch and the fry begin the next generation's accelerated race to sexual maturity.
In the aquarium, the standard technique mirrors this biology. A soft peat or coir substrate 1–2 in deep is provided in the breeding vessel; the pair spawns into it over days or weeks, after which the medium is removed, gently squeezed to reduce moisture without desiccating the eggs, and stored in a sealed container or plastic bag at room temperature. Wild incubation (eggs remaining in shallow water after pool refill) is reported to take as little as 2–4 weeks; the hobby standard of storing eggs in damp peat under diapause conditions typically yields hatching after 2–3 months of storage. Fry emerge at approximately 0.5 in total length — very small, requiring infusoria or commercial micro-fry food as a first food, graduating to nauplii as they grow. The American Killifish Association library documents the species' captive reproduction in detail across multiple issues of their journal, reflecting decades of hobbyist experience.
In the aquarium
Despite its small size, Fundulosoma thierryi rewards patient husbandry with strong colour displays and tractable breeding behaviour under the correct conditions. A species tank — or a pair or small group kept without other fish — is strongly preferred. Males are territorial with one another, and the species' diminutive size makes it a poor companion for anything larger. A tank of 5.5–10 US gal per pair is adequate.
A dark substrate — fine peat, dark sand, or a coir mixture — is both functionally necessary for breeding and aesthetically appropriate, as it intensifies male colouration. Low, diffuse lighting, floating plants or surface cover such as small Salvinia or Riccia, and leaf litter or coconut shells to provide cover and tannin staining all improve the species' comfort and willingness to display and spawn. Water chemistry should target the softer, slightly acidic to neutral range documented at collection sites: pH 6.0–7.2, temperature 72–79 °F. Good water quality is important — partial water changes are beneficial even though the species originates in pools that accumulate waste products naturally, since captive stocking densities are higher than wild ones.
Aquarium strains are available through killifish societies and specialist breeders, particularly through American Killifish Association (AKA) and British Killifish Association (BKA) networks. The documented locality strains — Ghana 94/1, K'palimé TOGO 1, Ada GH 06/5, and Mali — are maintained separately by collectors who value locality integrity; swapping strains with other hobbyists through club fish lists is the most reliable route to obtaining stock.
Conservation
The IUCN Red List assessment of October 2019, conducted by Diouf, Entsua-Mensah, and Lalèyè and published under version 2025-2, rates Fundulosoma thierryi as Least Concern. The assessment reflects the species' broad range across multiple countries and river basins — Senegal, Gambia, Mali, Burkina Faso (the former Upper Volta drainage), Niger, Ghana, and Togo — and the presence of 13 documented collection localities spanning several independent drainages. A species distributed this widely across West Africa's savanna zone is unlikely to face simultaneous threat across its entire range from any single pressure.
Nonetheless, the life history of an annual killifish tied entirely to temporary pool systems makes populations locally fragile. Seasonal pools are threatened by agricultural drainage, irrigation abstraction reducing wet-season flooding duration, and the conversion of savanna wetlands to arable land. The very short window of adult life and the complete dependence on pool-refill for egg hatching mean that even a modest reduction in the reliability of the wet season — through climate variability or upstream water abstraction — can locally extirpate populations before re-colonisation occurs. The species' ongoing representation in specialist killifish collections worldwide, with separately maintained locality strains preserved ex situ by club members, provides an informal insurance population of conservation value independent of any formal programme.