Taxonomy & naming
Nothobranchius steinforti was described by Rudolf Hans Wildekamp in 1977, based on material collected at a temporary pool near Kimamba in Tanzania's Wami River basin the previous year. It belongs to the large genus Nothobranchius — the East and Southern African annual killifishes — within the family Nothobranchiidae. Eschmeyer's Catalog of Fishes recognises the valid name as Nothobranchius steinforti Wildekamp, 1977.
The species was named in honour of Theo Steinfort, a Dutch aquarist who contributed to the collection or study of the type material. This eponymous naming is a tradition in Nothobranchius taxonomy, where many species carry the names of the hobbyist-collectors who first brought them to science's attention — an acknowledgment of the outsized role dedicated killifish enthusiasts have played in documenting this speciose genus across eastern Africa.
Within the genus, N. steinforti is placed among the East African Nothobranchius of the coastal-drainage assemblage. No subspecies are recognised. The Kimamba T 76-4 strain designation used in hobbyist records encodes the type locality (Kimamba), the taxon initial (T for Tanzania-coast group, in some registries), and the year of collection (76), followed by a collection-event number.
Morphology
Nothobranchius steinforti is a compact, laterally compressed killifish reaching a maximum of 2 in total length (FishBase), typical for an annual Nothobranchius of the East African coast. The body form is robust relative to size, with a blunt head, upturned mouth, and the deep caudal peduncle characteristic of the genus.
As in all Nothobranchius, sexual dichromatism is pronounced. Males are brilliantly coloured, displaying the vivid reds, blues, and iridescent scale-patterning that characterise the genus and drive their popularity with specialist hobbyists. Females are cryptically coloured — plain brown or olive, smaller, and more slender — a typical pattern in annual killifishes where intense male coloration is linked to short-season mate selection under time pressure imposed by the drying pool environment.
The fins of males are typically edged or patterned with contrasting colour, and the caudal fin may show banding or lyre-like extension. Detailed colouration notes from aquarists maintaining the Kimamba T 76-4 strain are sparse in the literature, reflecting how seldom this species has been studied relative to more common Nothobranchius such as N. rachovii or N. furzeri.
Habitat
The species is known only from the upper Wami River drainage in eastern Tanzania, a region of seasonal savanna and agricultural land where rainfall is strongly seasonal. Its habitat consists of shallow ephemeral pools — depressions that fill with the rains and dry completely during the dry season. These pools are typically turbid, with soft sediment substrates of mud, leaf litter, and organic detritus, and may be shaded by grass or low woody vegetation at their margins.
Water conditions in such habitats tend toward the soft and mildly acidic end of the spectrum, warmed by the equatorial sun; hobbyist records and the FishBase temperature range of 75–82 °F reflect conditions typical of lowland East African seasonal pools. The pools may also include flooded rice field margins where agricultural land borders the drainage.
The IUCN records the area of occupancy as just 5 mi², and the species is known from only two nearby sites — the type locality and one additional location documented in surveys. Multiple dedicated searches since the 1976 collection have failed to find living specimens, despite successful collection of other Nothobranchius species in the same general area, suggesting that N. steinforti's specific habitat microhabitat may have been eliminated or degraded beyond use.
Feeding
Like all Nothobranchius, N. steinforti is a carnivore in the wild. The ephemeral pool habitat of East African annual killies supports seasonal pulses of aquatic invertebrates — chironomid larvae, small crustaceans, aquatic insect larvae, worms, and zooplankton — that constitute the bulk of the diet. The upturned mouth is adapted for surface or mid-water feeding on invertebrate prey, and the fast growth rate of annual species means energy intake during the brief wet season is critical for reaching sexual maturity before pool desiccation.
In captivity, N. steinforti accepts live and frozen invertebrate foods: daphnia, artemia (brine shrimp), bloodworm (Chironomus larvae), tubifex, and small whiteworm. Dry prepared foods may be taken by some individuals. Varied, protein-rich feeding supports the rapid growth and conditioning necessary for successful breeding with this species, whose short natural lifespan means captive individuals are often maintained under a compressed schedule of feeding and spawning cycles.
Mating
Nothobranchius steinforti is an annual killifish with a substrate-spawning mating system driven entirely by the impending desiccation of its pool habitat. In the wild, males establish territories and display intensely to females against the compressed backdrop of a wet season that may last only weeks to a few months. The vivid male colouration serves as a fitness signal under this time pressure, and mate choice is correspondingly intense.
Spawning occurs when a receptive female approaches a displaying male. The pair align side by side and dive together into the soft substrate — mud, peat, or leaf detritus — where a single egg is deposited and fertilised at depth in the sediment with each spawning act. This dive-and-deposit behaviour is repeated multiple times per session; a productive pair may spawn dozens of eggs across a breeding bout. The eggs are left entirely buried, with no further parental attention.
Breeding
The breeding biology of N. steinforti follows the canonical annual Nothobranchius pattern. Eggs buried in the pool substrate enter embryonic diapause — a state of arrested development that allows the embryo to survive the complete desiccation of the pool through the dry season. Development resumes when the pool refills with the next rains, and fry hatch rapidly, growing to sexual maturity in six to ten weeks in the burst of food availability the wet season provides. Wild fish may complete their entire reproductive cycle and die within a single wet season of under a year.
In captivity, hobbyists replicate this cycle using peat moss or coconut coir as a spawning medium. Pairs are placed over the medium for a period of weeks to collect eggs; the medium is then removed, lightly pressed, and stored dry in sealed bags or containers at room temperature. WildNothos documentation indicates an incubation period of three to six months for the Kimamba T 76-4 strain, after which the peat is re-wetted and fry hatch within days. Killi.co.uk hobbyist records describe the species as very difficult to breed successfully — fry survival has been poor in most attempts, nearly all surviving offspring have been female in some lines, and the captive population is maintained by only a small number of specialists. The difficulty underscores the fragility of the sole surviving gene pool.
In the aquarium
Nothobranchius steinforti is a species for the dedicated killifish specialist, not a general aquarium fish. Its extreme rarity in captivity — all stock tracing to a single 1976 collection — means that maintaining the Kimamba T 76-4 strain carries genuine conservation responsibility. The species is listed by killifish organisations and WildNothos as one of several Nothobranchius of conservation concern held in cultured lines, and hobbyist breeders are encouraged to communicate, exchange stock, and coordinate breeding efforts to prevent inbreeding collapse.
FishBase notes the species is very difficult to maintain in the aquarium, a sentiment echoed by killi.co.uk records of poor fry survival and skewed sex ratios. Aquarium water should be soft and acidic, consistent with its eastern Tanzanian pool origin, and temperatures in the range of 75–82 °F are appropriate. A small, well-covered species tank with a peat or coir substrate layer for spawning and minimal tankmates is the standard setup. Water changes must be regular and gentle — small, aged water additions rather than large sudden changes suit the shallow-pool conditions the fish evolved in.
Given the failure of multiple field surveys to locate wild populations, the captive Kimamba T 76-4 strain may represent the entire living population of this species. Hobbyists who maintain it are, in a real sense, acting as a last refuge.
Conservation
The IUCN Red List assessment of 12 January 2019 places Nothobranchius steinforti as Critically Endangered, with the qualifier 'Possibly Extinct in the Wild'. The criterion is B2ab(iii,iv): the area of occupancy is estimated at just 5 mi², there is a single threat-based location, and there is inferred continuing decline in the extent and quality of habitat (criterion iii) and in the number of locations (criterion iv).
The primary identified threat is progressive agricultural expansion and habitat degradation in the upper Wami River area. The shallow ephemeral pools used by annual killifishes are among the most vulnerable freshwater habitats on Earth — easily drained, ploughed, or altered for rice cultivation, cattle watering, or small-scale farming. Even modest changes to pool depth, permanence, or substrate character can disrupt the soil-spawning breeding cycle that annual killies depend on. The IUCN assessment notes that the last confirmed wild collection was in 1976, and that multiple subsequent surveys have failed to find the species despite successfully finding other Nothobranchius in the same general area.
Conservation action for N. steinforti centres almost entirely on the captive hobbyist population. WildNothos, the KFN (Killi-Fisch-Netzwerk), and affiliated killifish clubs maintain records of the Kimamba T 76-4 strain's distribution among breeders and encourage genetic diversification within the available stock. Field surveys of the upper Wami drainage during the wet season, when ephemeral pools are full, would be the critical next step in determining whether any wild population persists — but as of the 2019 assessment, the species' status in the wild remains uncertain and the outlook is grave.