Taxonomy & naming
Nothobranchius polli was described by Rudolf H. Wildekamp in 1978 from material collected at the Dilungu swamp in the Lufira River drainage, Katanga Province, DR Congo (holotype MRAC 192399, a male of 1 in SL). Eschmeyer's Catalog of Fishes (Fricke, Eschmeyer & Fong) records the valid name as Nothobranchius polli Wildekamp, 1978 within the family Nothobranchiidae.
The species belongs to the subgenus Zononothobranchius and is placed in the N. brieni species group — a cluster of annual killifishes largely confined to the Congolese plateau and its surrounding drainages. A notable cytogenetic feature sets N. polli apart from its relatives: a karyotype of 2n = 36, NF = 60, which is unique within the genus and has been noted in the scientific literature as a potential character of taxonomic value.
The species was named in honour of Prof. Max Poll (1908–1991), the Belgian ichthyologist at the Royal Museum for Central Africa (Tervuren) who devoted much of his career to describing the freshwater fishes of the Congo Basin and was instrumental in building the type collection from which Wildekamp drew his material.
Morphology
Males reach a maximum recorded size of approximately 1.5 in SL (WildNothos database); FishBase gives a maximum total length of 2.5 in TL. The body is laterally compressed, moderately deep, and typical of the genus in overall build. Sexual dichromatism is pronounced: females are cryptically coloured and substantially less vivid than males.
Male colouration is striking. The body is iridescent light blue with red scale margins forming a fine red reticulation across the flanks. The snout, throat, and dorsal surface of the head carry a warm red flush. The dorsal fin is pale blue with dark red stripes and a light blue distal band. The anal fin is pale blue with red bands and yellow distal portions. The caudal fin is pale blue with red marbling, a brown medial band, a light blue subdistal band, and a black distal margin — a pattern characteristic of species in the Zononothobranchius subgenus. Females lack these ornaments and are a plain brownish-olive.
Habitat
Nothobranchius polli is restricted to the upper Lufira River drainage of Katanga Province, southeastern DR Congo, at elevations between approximately 1,059 and 1,226 ft above sea level. It inhabits the shallow, seasonal freshwater habitats of this high-altitude savanna: water-filled depressions locally called dembos, temporary swamps, ditches, and floodplain pools that exist only during and shortly after the rainy season.
Field measurements recorded by WildNothos observers document water temperatures of 73–82 °F, pH 6.32–7.18, total dissolved solids of 101–193 ppm, and conductivity of 202–386 µS — moderately mineralised, near-neutral to slightly acidic water consistent with open savanna runoff pooling in clay-rich depressions. This is not the blackwater or strongly acidic soft water typical of some West African annual killifishes; the Lufira pools sit at higher elevation and draw from a different geological substrate than the lowland Congo Basin systems.
Because the pools dry completely each year, the species has no permanent wetland habitat anywhere in its known range. Its entire distributional footprint consists of ephemeral features that vanish for months at a time, leaving only buried eggs to carry the population through the dry season.
Feeding
Like other members of the genus, N. polli is a generalist micro-predator in the wild, taking the invertebrate fauna that colonises its seasonal pools shortly after they fill: aquatic insect larvae, small crustaceans, zooplankton, and worms. The species is not documented in the literature as specialised in any particular prey type; its ecology matches the opportunistic feeding behaviour recorded for other Nothobranchius from similar savanna-pool habitats.
In the aquarium, Poll's notho accepts live and frozen small foods readily — artemia nauplii, daphnia, cyclops, chironomid (bloodworm) larvae, and similar invertebrate material. Varied feeding with live or frozen prey maintains condition and colour in males. Prepared foods can be offered but are typically less eagerly accepted.
Mating
Nothobranchius polli is an annual killifish and a substrate-spawner: males court females with lateral displays that showcase the iridescent blue-and-red flank colouration and the banded fins. Pair formation is brief, and spawning takes place at the bottom of the pool.
During spawning the pair dive together into the soft substrate — mud, peat, or detritus — where the male wraps around the female and eggs are deposited directly into the material as the pair wriggle downward. Each spawning act deposits only a small number of eggs, but pairs spawn repeatedly over the course of hours or days. The eggs are left buried in the substrate with no further parental involvement; the adults do not guard or tend the nest. This bottom-spawning mode in soft substrate is characteristic of the annual Nothobranchius and contrasts sharply with the plant-spawning behaviour of non-annual killifishes.
Breeding
The eggs of N. polli undergo obligate diapause: as the pool dries and the adult fish die, the buried eggs enter a state of arrested development that allows them to survive the dry season in the soil. When the rains return and refill the pool, the eggs hatch rapidly and the juvenile fish begin feeding almost immediately — a strategy that compresses the entire productive life of each generation into a single wet season.
In aquarium husbandry, spawning is carried out on peat moss, coir fibre, or a similar soft medium placed in a small container on the tank floor. Pairs are conditioned on live or frozen foods and introduced to the spawning container for periods of one to several weeks. The medium is then removed, lightly squeezed to remove excess water, and stored in a sealed, labelled plastic bag at room temperature. WildNothos records an embryonic development period of three to four months at room temperature for this species before hatching is triggered by re-wetting the medium. Emerging fry are relatively large for the genus and take artemia nauplii immediately. Growth is rapid; fish can reach sexual maturity in as little as eight to ten weeks under warm, well-fed conditions, reflecting the evolutionary pressure to reproduce quickly within a seasonal window.
In the aquarium
Poll's notho is maintained by specialist annual killifish keepers and is not a common aquarium fish. A pair or small group (one male, two or three females) can be housed in a small, well-planted aquarium of 10–15 US gal with a tight-fitting lid and gentle filtration; the males are bold but not notably aggressive toward other small fish that are too large to eat, though multiple males will display and compete. Water temperature of 72–82 °F and pH close to neutral are appropriate given the field data; extremes of temperature or chemistry should be avoided.
The hobby keeps the species primarily through the peat-spawning cycle described above. Because the wild fish are annual and short-lived, captive populations depend entirely on successful diapause management: labelled storage bags with accurate dates, appropriate temperature during storage, and timely re-wetting are the practical skills that separate successful breeders from those who lose populations between generations. The species is traded within the killifish specialist community, primarily through killifish association auctions and member exchanges rather than through general retail channels.
Conservation
The IUCN Red List assessment of Nagy & Watters (2019) places Nothobranchius polli in the Endangered category under criterion B1ab(iii)+2ab(iii), reflecting the species' extremely restricted range — confined to the upper Lufira drainage — and evidence of ongoing decline in the extent and quality of its seasonal wetland habitat. The Lufira basin lies within the Katanga Copperbelt, one of sub-Saharan Africa's most heavily industrialised regions; mining activity, associated infrastructure, and agricultural expansion around Likasi and Kolwezi place direct pressure on the temporary floodplain pools and dembos that constitute the species' entire habitat.
A broader conservation review by Nagy & Watters (2021) found that approximately 72% of the 94 described Nothobranchius species are threatened with extinction — a proportion reflecting the genus's near-universal dependence on seasonal ephemeral wetlands that are disappearing across Africa as land use intensifies. N. polli faces the compounded risk of a very small extent of occurrence and a habitat type that is both inherently fragile (destroyed by any drainage or compaction of the pool floor) and poorly protected within the existing reserve network of Katanga Province.
No captive assurance colony for this species is formally documented in the published literature, though it is maintained by killifish hobbyists. Its long-term survival depends on the persistence of intact seasonal floodplain habitat in the upper Lufira — a landscape under sustained anthropogenic pressure with no current evidence of recovery.