Taxonomy & naming
Nothobranchius wattersi was formally described by Lothar Seegers in 1983, and Eschmeyer's Catalog of Fishes (CAS) records that valid name and authority. The species is a member of the large genus Nothobranchius — a radiation of around 70 or more annual killies distributed across sub-Saharan Africa, particularly the coastal plain rivers and interior basins of East and southern Africa.
For many years N. wattersi was poorly delimited from N. kirki, and it was commonly referred to in killifish literature and the hobby as N. kirki or as N. aff. kirki. A 2013 review by Ng'oma and colleagues established its taxonomic identity more firmly, placing it on more secure ground as a distinct species and clarifying the characters that separate it from its close relatives.
The specific epithet wattersi honours Brian Watters, a killifish researcher and collector whose fieldwork in Malawi and surrounding regions contributed substantially to knowledge of East African annual killies. The type locality is recorded as temporary roadside pools 6–7 mi east-northeast of Salima, Salima District, Malawi (approximately 13°46'S, 34°33'E), along road S29.
Morphology
FishBase records a maximum standard length of 2 in for N. wattersi, placing it among the small to medium-sized members of the genus. As in all Nothobranchius, there is pronounced sexual dimorphism: males are brilliantly coloured, while females are a cryptic brownish-grey that offers camouflage in the turbid, silt-laden pools they inhabit.
Male colouration in this species follows the intense pattern typical of East African annual killies — a mosaic of iridescent scales producing vivid blues, reds, and/or oranges against dark scale edges, with caudal-fin coloration that varies between populations. The body form is fusiform and stocky, built for rapid bursts in shallow, structurally simple water bodies. The dorsal and anal fins are positioned far back on the body, above and below each other, facilitating the tight spawning embrace used during peat-diving. Females are plainly coloured, rounded in the belly when gravid, and slightly smaller than males at maturity.
Habitat
Nothobranchius wattersi is endemic to Malawi, with its range centred on the floodplain systems associated with the central and southern end of Lake Malawi, the Lake Malombe basin, and the upper Shire River region. It occupies ephemeral pools, swamps, and roadside ditches on floodplains — habitats that exist only during and shortly after the rainy season and dry out completely each year.
The substrate of these pools is characteristically fine black or grey clay-rich soil: silt, mud, and fine sand in combination. This soft, penetrable substrate is critical to the species' reproductive biology, since eggs are buried in the uppermost layers by spawning adults. The overlying water is typically warm, shallow, and relatively exposed to sunlight.
Water parameters recorded by Watters (1991) from sites within the species' range span temperature 79–95 °F and pH 6.5–8.1, with total dissolved solids of 30–280 ppm — a range from soft to moderately hard water. This breadth reflects variation across sites and seasons rather than any single pool's profile; individual pools may be considerably softer or harder depending on local geology and evaporation concentration as the dry season approaches.
Feeding
Nothobranchius wattersi is a carnivore, as is typical for the genus. In the wild, the diet consists primarily of small invertebrates: aquatic insect larvae (chironomids, mosquito larvae), microcrustaceans (cladocerans, copepods), and other zooplankton that bloom in productive ephemeral pools following the rains. The protein-dense invertebrate fauna of newly flooded grassland pools fuels the rapid growth and early sexual maturation that annual killies require to reproduce before their habitat disappears.
In captivity, N. wattersi accepts live and frozen invertebrate foods readily — bloodworm (Chironomus larvae), brine shrimp (Artemia), daphnia, and mosquito larvae are all appropriate and maintain condition well. Varied feeding with appropriately sized live or frozen prey keeps colour and health at their best; like many Nothobranchius, the species can be persuaded to take high-quality small pellets or granules but performs best on predominantly meaty foods.
Mating
As an annual killifish, N. wattersi follows the characteristic Nothobranchius mating pattern centred on competitive male display and substrate-spawning. Males in breeding condition display intensely to females and to one another: lateral spreading of fins, body colouration at its most vivid, and frequent short chases establish dominance hierarchies in the shallow pools. A receptive female is courted with persistent fin-spreading and nudging alongside her.
Spawning itself is a brief, vigorous embrace: the male curves tightly around the female, pressing her against the pool bottom. Together, the pair drive several centimetres into the soft substrate — a behaviour called peat-diving in the hobby — and release a single egg and sperm simultaneously into the sediment. The egg is immediately buried. The pair surface, rest briefly, and repeat the sequence multiple times over a spawning session; each session deposits individual eggs scattered through the uppermost substrate layer rather than a single mass clutch. There is no pair bond and no territorial defence of spawning sites beyond the short duration of each embrace.
Breeding
The eggs of N. wattersi are adapted for survival through months of total desiccation. After the adults deposit eggs in the clay substrate, the pool level drops as the dry season advances; the eggs remain buried in the now-dry sediment in a state of embryonic diapause, their development arrested at one or more developmental checkpoints. This arrested development can last through the entire dry season — several months under natural conditions — until the return of rains re-wets the substrate and triggers hatching.
In the hobby, the standard breeding method replicates this biology closely. Breeders provide a container with several centimetres of soft peat or coir fibre as spawning medium, which the fish rapidly begin to use. After a few weeks of spawning, the peat is removed, gently squeezed to remove most moisture but not dried completely, sealed in a plastic bag or container labelled with the collection date, and stored at room temperature (typically 75–82 °F) for a diapause period. WildNothos data for this species indicates an embryonic development period of approximately 3–5 months in peat at room temperature before hatching rates peak. At the end of the diapause period the peat is re-wetted with soft, aged water; fry hatch within 24–48 hours and require immediate feeding with infusoria or commercial fry food, graduating rapidly to Artemia nauplii. Growth is fast and fish can reach sexual maturity within 6–8 weeks of hatching.
In the aquarium
Nothobranchius wattersi is a rewarding species for the specialist killifish keeper but is not a general community fish. Its small size and brief adult lifespan — wild fish live only a single season, and captive individuals rarely exceed 12–18 months — mean it demands a keeper who understands and embraces the annual lifecycle rather than expecting a long-lived display animal.
A small, species-only tank of 10–15 US gal suits a pair or trio well. Water should be soft to moderately hard (matching the 30–280 ppm TDS range documented in the wild), temperature 75–82 °F, and pH around 6.5–7.5; some additional tannin staining from peat filtration or driftwood is beneficial and reflects natural conditions. Filtration must be gentle — strong currents are inappropriate for a species adapted to still, shallow pools. A dark substrate and subdued lighting bring out male colouration best.
Given the competitive nature of males, it is advisable to keep one male per female or to provide multiple females per male to distribute spawning pressure. Dense low-level planting or floating cover gives females refuge. The keeper should provide a dedicated peat or coir spawning tray at all times for egg collection. Regular water changes and varied feeding maintain peak colour and health in what can otherwise be a short captive life. N. wattersi is best kept and bred by hobbyists already familiar with the annual killifish cycle through experience with other Nothobranchius species.
Conservation
The IUCN Red List assessed Nothobranchius wattersi as Near Threatened (NT) in 2018, based on an assessment by Nagy, Watters, and Tweddle. The Near Threatened designation reflects genuine concern: the species is a single-country endemic confined to a narrow strip of floodplain habitat in central and southern Malawi, and the temporary pool systems it depends on are intrinsically vulnerable to both natural variability and human-driven change.
The principal threats are habitat loss and degradation. Malawi's floodplains face pressure from agricultural expansion, drainage of seasonal wetlands for cultivation, and infrastructure development including road construction that modifies the hydrology of precisely the kind of roadside ditch and low-lying pool habitat in which the type locality was recorded. Water abstraction for irrigation, introduced species such as mosquitofish (Gambusia affinis), and increased sedimentation from catchment deforestation all compound the risk. Because N. wattersi's eggs are confined to the substrate of specific pools, the loss of even a small number of occupied sites can represent a meaningful proportion of the global population.
The species is maintained in hobbyist collections, and the killifish keeping community — through organisations such as the American Killifish Association — has historically played a role in sustaining ex-situ populations of threatened Nothobranchius species whose wild habitats are under acute pressure. Conservation of the species in the long term, however, depends on protecting and restoring the seasonal floodplain wetlands of the Lake Malawi and Lake Malombe drainage that form its only known habitat.