Taxonomy & naming
Nothobranchius seegersi was described by Rudolf Hans Wildekamp in 1994, placing it within the large African annual killifish genus Nothobranchius. The genus belongs to the family Nothobranchiidae, the African killifishes, a clade of teleosts defined by their annual life history in seasonally desiccating habitats across sub-Saharan Africa. Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) treats Nothobranchius seegersi Wildekamp, 1994 as the valid combination.
Subsequent collection records from the Wulua River drainage have confirmed the species' presence in the Malagarasi basin and provided additional material for study. The Biodiversity Heritage Library preserves notes on specimens collected from ephemeral water bodies in this drainage, and a 2011 contribution by Valdesalici and Kardashev in the Bonn zoological Bulletin (60: 89–93) further documented the species from the region. The type locality is a small, shallow pond — approximately 3 × 16 ft in extent and no more than 10 in deep — set in open woodland, without aquatic vegetation.
Morphology
Nothobranchius seegersi is a compact annual killifish. FishBase records a maximum standard length of 2.5 in for males (and unsexed individuals), with females somewhat smaller at around 2 in SL — proportions typical of mid-sized Nothobranchius. The body is laterally compressed, relatively deep through the anterior trunk, and tapers to a rounded caudal fin, the body plan common to the genus.
Males display the vivid, sexually selected colouration characteristic of East African Nothobranchius: patterned flanks with iridescent scales and contrasting fin markings. Females are considerably plainer, showing the typical cryptic olive-to-brown background colouration that affords camouflage in the turbid, brown, sediment-rich water the species inhabits in nature. Sexual dichromatism is pronounced and conspicuous, making the sexes easy to distinguish at a glance — a feature common to the genus and important for identifying pairs in the aquarium.
Habitat
Nothobranchius seegersi is endemic to the Malagarasi River basin in central Tanzania, where it inhabits ephemeral pools in the Wulua and Mungu river drainages. The Malagarasi is one of Tanzania's major westward-flowing river systems, draining into Lake Tanganyika. The seasonal pools occupied by N. seegersi are shallow, small, and typically turbid; WildNothos describes the water as brown and very turbid — conditions created by the soft, organically rich substrate disturbed by rainfall and the activity of the fish themselves.
The FishBase record for the type locality gives indicative water parameters of 72 °F, pH 7, and a hardness of approximately 5 dH — relatively soft and close to neutral, reflecting the character of Tanzanian savanna and open-woodland drainage waters. The pools have no aquatic vegetation, consistent with the species' substrate-spawning biology, and the surrounding habitat is open woodland. These pools fill during the wet season, contract and disappear entirely in the dry season, and refill the following year — the defining ecological rhythm to which the entire life cycle of the species is precisely adapted.
Feeding
Like other Nothobranchius, N. seegersi is a carnivore in the wild, feeding opportunistically on small invertebrates available in its shallow, seasonal pool habitat. These prey items typically include aquatic insect larvae (chironomid midges, mosquito larvae), small crustaceans, worms, and other zooplankton — the invertebrate fauna that colonises and proliferates rapidly in newly flooded pools.
In the aquarium the species accepts a wide range of live and frozen foods without difficulty. Small live foods such as Artemia nauplii, Daphnia, microworms, and mosquito larvae are ideal conditioning foods and trigger natural foraging behaviour. Frozen bloodworm, Cyclops, and similar items are readily taken. Providing variety in the diet supports colouration and breeding condition, particularly in males. Being a small fish with a small gape, prey items should be sized accordingly.
Mating
Nothobranchius seegersi is an annual killifish whose mating system is built around the imperative of producing drought-resistant eggs before the pool dries out. Males are brightly coloured and actively court females with lateral displays, spreading their fins to show the full extent of their patterning. Competition between males for access to females is intense — a consequence of the compressed breeding season and the tight spatial confines of a small seasonal pool.
When a pair has formed, the male drives the female toward the substrate. Spawning is a brief, rapid event in which both fish dive into the soft mud or peat of the pool bottom, with the eggs deposited and fertilised within the substrate itself. This substrate-diving behaviour is the defining feature of peat-spawning annuals within Nothobranchius and the mechanism by which eggs are placed where they can survive desiccation. Multiple spawning dives occur across the breeding season, with females depositing small numbers of eggs per dive.
Breeding
The breeding biology of N. seegersi follows the annual template shared by all members of the genus. Fertilised eggs are left buried in the substrate of the seasonal pool. As the dry season advances and the pool contracts and ultimately disappears, the eggs remain dormant in the now-dry soil, protected by a tough chorion. The embryos enter diapause — a state of suspended development — and can remain viable in dry storage for weeks or months depending on species and conditions, hatching rapidly when the pool refills at the start of the next wet season. Adults do not survive the dry season; the population persists entirely as eggs in the soil.
In the aquarium, this life cycle is replicated by spawning the fish on a layer of peat moss or coconut coir substrate. After a suitable spawning period, the moist peat is collected, gently squeezed to remove excess water, and stored in a sealed plastic bag or container at room temperature — typically for two to four months, though storage duration can be adjusted based on embryo development checks. Re-wetting the peat triggers hatching. Fry are immediately free-swimming and large enough to accept freshly hatched Artemia nauplii from the first day. Growth is fast; males begin to show colour within a few weeks, and the fish can reach sexual maturity in under three months, reflecting the short wild life cycle.
In the aquarium
Nothobranchius seegersi is kept primarily by specialist killifish hobbyists, particularly those with an interest in African annual species. It is not a demanding fish in terms of water chemistry, given its origin in soft, slightly acidic to neutral waters, but it does require the specific husbandry that all annual Nothobranchius demand: a peat or coir spawning substrate, periodic removal and dry-storage of eggs, and the patience to manage the annual cycle of spawning and incubation.
Because wild fish live less than a year, aquarium specimens age quickly and should be set up for spawning promptly. A small, well-filtered tank (10–15 US gal is adequate for a pair or trio) with a dark substrate, some floating plants or surface cover to reduce light intensity and aggression, and a suitably deep layer of peat or coir for spawning is the standard setup. Temperature should be maintained around 72–79 °F. Males can be aggressive with one another, so pairs or trios (one male, two females) are preferable to groups of multiple males in confined quarters. The British Killifish Association and the American Killifish Association both maintain hobbyist resources and egg-distribution networks for annual species including N. seegersi.
Conservation
The IUCN Red List assesses Nothobranchius seegersi as Vulnerable under criterion B1ab(iii), assessed by Nagy and Watters in 2019. The B1 criterion reflects a restricted extent of occurrence — the species is known from a limited number of locations in the Wulua and Mungu river drainages of the Malagarasi basin in central Tanzania — and the 'ab(iii)' qualifier indicates that the area, extent, or quality of habitat is inferred to be in continuing decline.
The threats facing N. seegersi are those common to small-pool annual killies across East Africa: drainage and conversion of seasonal wetlands for agriculture, alteration of catchment hydrology through deforestation and land clearance that changes the flooding and drying regime on which the species depends, and potential impacts from introduced fish. Because the entire population at any location persists only as eggs in the soil during the dry season, any disturbance that physically destroys the substrate — ploughing, road construction, livestock trampling — at the wrong moment can eliminate a local population entirely. The species' restricted range and the ephemeral, highly localised nature of its habitat make it particularly vulnerable to even small-scale land-use changes.