Rainbow Killifish

The Rainbow Killifish, Nothobranchius rachovii, also known as the Bluefin Notho, is a small annual killifish in the family Nothobranchiidae, native to temporary floodplain pools in coastal Mozambique. Like other Nothobranchius species, it is adapted to a seasonal boom-and-bust life cycle tied to the filling and drying of shallow rain-fed pools. It is among the most vividly colored killifish species and has long been popular in the aquarium hobby, with several geographic color forms recognized from different localities. The species remains present across suitable temporary-pool habitat within its native coastal Mozambique range.

Identification points for Nothobranchius rachovii:

• Compact, deep-bodied fish, typically 5-6 cm as an adult
• Males display intense iridescent blue-green scale coloring overlaid with a red-orange reticulated (net-like) pattern across the body
• Rounded caudal fin edged in black with a red-orange band; dorsal and anal fins carry similar banded coloration
• Females are plain grey-tan with minimal pattern, showing strong sexual dimorphism typical of Nothobranchius
• Distinguished from the similarly colored Turquoise Killifish by its more rounded fin shape and reticulated, rather than barred, body pattern

Rainbow Killifish inhabit small, shallow, temporary pools that form in coastal floodplain depressions during Mozambique's rainy season and dry out completely in the dry season. These ephemeral habitats are typically warm and turbid, with soft mud substrate into which the species' drought-resistant eggs are buried to survive the dry months. As an obligate annual species, it has no permanent aquatic habitat as an adult, relying entirely on the temporary pool's brief existence to complete its rapid life cycle before conditions become unsuitable.

Rainbow Killifish grow and mature extremely rapidly after hatching, reaching breeding condition within weeks in order to reproduce before their temporary pool evaporates. Adults are active, solitary predators that feed on small aquatic invertebrates such as insect larvae and zooplankton near the surface and mid-water. Males display vivid coloration and compete for females, with spawning occurring repeatedly through the short adult lifespan; fertilized eggs are buried in the mud substrate and enter diapause, allowing them to survive desiccation until the pool refills with the next rains. This rapid life history makes it an ecologically important, short-lived predator within its temporary wetland habitat.