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Nothobranchius rachovii is a small annual African killifish known for its brilliant colours and its life cycle adapted to seasonal pools. Native to Mozambique, it inhabits temporary depressions that fill during the rainy season and dry out during the dry season. This strategy explains its rapid growth, early maturity and production of eggs able to survive for months in damp substrate. In an aquarium, this fish is best suited to aquarists who enjoy observation, breeding and careful water management. Males are especially colourful, while females remain more subdued. Very common in the specialist aquarium trade, it still requires attentive care, stable conditions and suitable food.

General species description

Nothobranchius rachovii is an annual killifish belonging to the family Nothobranchiidae. Its life follows the rhythm of rainfall: adults quickly colonize newly filled pools, reproduce within a short period, and die when the water evaporates. The eggs remain buried in the substrate and hatch after the pool is refilled, when moisture and temperature become suitable. This unusual biology requires a different approach from that used for permanent tropical fish. In aquariums, it is usually kept in groups, with particular attention to water quality, oxygenation and prevention of jumping. The male may defend a small territory near the bottom, but the species is not an aggressive predator toward similarly sized fish. Its main appeal is the observation of its annual life cycle, spawning behaviour and rapid development of colour. A species-only setup is often the simplest and safest option.

Geographical origin and habitat

Country of reference: Mozambique. The species is associated with the lower basin of the Pungwe River, in a region of floodplains and temporary depressions. It occurs in shallow pools formed during the rainy season rather than in permanent streams. These habitats may be isolated from one another, and their water level changes greatly throughout the year. The water is generally still and may be lightly stained by organic matter from the surrounding soil. The bottom consists of mud, fine sand and plant debris, while grasses or seasonal plants grow around the edges. The water is usually shallow, ranging from a few centimetres to less than half a metre. In an aquarium, gentle filtration, a dark substrate and open areas near the bottom recreate its habitat better than strong circulation. A temperature of 22 to 28 °C and a pH of approximately 6.0 to 7.5 are generally suitable.

Precise location and local name

Historic populations are associated with the lower Pungwe floodplain, around Beira in central Mozambique. This region includes marshy areas and temporary pools linked to cycles of flooding and falling water levels. Nothobranchius rachovii does not have a widely established Mozambican local name in the commonly used aquarium literature. The most frequent aquarium vernacular name is “Rachov’s killifish” or “Rachov killie.” As with many annual killifish, the exact origin of a strain is important: two populations may differ in colour, size or egg-dormancy period. To preserve the value of separate lineages, fish from different localities should be maintained separately and their origin should be recorded. This also helps prevent accidental mixing during breeding and makes it easier to track geographical strains. Clear records are especially useful when exchanging eggs or young fish with other killifish keepers.

Appearance and physical characteristics

The body of Nothobranchius rachovii is elongated, laterally compressed and covered with small scales. The adult male generally displays spectacular colours, combining red, orange, blue and metallic reflections. The dorsal, anal and caudal fins are well developed and may show contrasting edges. The female is smaller or slimmer in appearance and has a greyish brown to beige colour, with much less colourful fins. The difference between the sexes becomes visible at a fairly young age, making it easy to assemble a breeding group. Maximum adult size is about 7 cm, although males usually appear larger because of their fins and colour. Its streamlined body and broad fins are suited to movement in shallow, calm water. Colour becomes stronger with a good diet, moderate lighting, a dark substrate and stable social conditions. Males may chase and challenge one another, particularly around spawning sites. The male’s intense coloration is the species’ most distinctive aquarium feature.

General diet

In nature, Nothobranchius rachovii mainly feeds on small prey available in temporary pools, including insect larvae, tiny crustaceans, worms and other aquatic invertebrates. It is a carnivorous-leaning fish that responds especially well to moving foods. In an aquarium, offer brine shrimp, daphnia, bloodworms and other suitably sized frozen or live foods. Young fish benefit from very small prey such as newly hatched brine shrimp, offered in several small meals. Carnivorous pellets may be accepted, but they should not be the only food at the beginning. A varied diet supports growth, colour and reproduction. Remove uneaten food to protect water quality, since protein-rich meals break down quickly in a small aquarium. A moderate ration offered once or twice daily suits healthy adults. The priority is food that is high in protein and sufficiently varied, with live or frozen foods used regularly when possible.

Essential data

• Native river: Pungwe River
• Local name used: No widely established Mozambican local name; Rachov’s killifish in aquaria
• Origin of the scientific name: The generic name refers to a false gill; the specific epithet honours Arthur Rachow
• Full-name etymology: Nothobranchius comes from the Greek nothos, false, and branchion, gill; rachovii is formed from the name Rachow
• Common/vernacular names: Rachov’s killifish, Rachov killie, Rachow’s notho
• Family: Nothobranchiidae
• Subfamily: Nothobranchiinae
• Name pronunciation: no-tho-BRAN-kee-us ra-KHO-vee-eye
• Discovery: Ernst Ahl, 1926
• Maximum adult size: About 7 cm
• Water temperature and pH: 22 to 28 °C; pH 6.0 to 7.5
• Watercourse appearance and surrounding vegetation: Shallow temporary pools with still water, muddy or sandy bottoms, grasses and seasonal vegetation
• Typical tank mates: Best kept in a species-only group with conspecifics
• Temperament and behaviour: Active, territorial during spawning and generally peaceful outside male competition
• Water depth: Approximately 10 to 40 cm in seasonal pools
• Sexual dimorphism: Male much more colourful and often larger; female beige-grey and more subdued
• Bottom structure and flow: Mud, fine sand and plant debris; stagnant or very slow-moving water

In your aquarium

Success with Nothobranchius rachovii depends on a covered, well-oxygenated aquarium with gentle circulation, a dark substrate and plant cover. Keeping several females per male helps reduce the pressure caused by courtship and chasing. Breeding requires a suitable spawning medium, such as peat or a dedicated spawning container, so eggs can be collected without mixing them with waste. Water quality should be monitored closely, and the fish should receive a varied diet while overly fast or aggressive tank mates are avoided. By respecting its annual rhythm and dietary needs, aquarists can enjoy a colourful, active fish that is especially rewarding to breed.