Redtail Notho

The redtail notho (Nothobranchius guentheri) is a small annual killifish in the family Nothobranchiidae, native to Zanzibar Island and coastal Tanzania. It belongs to a large East African genus of "annual" killifish adapted to life in temporary rain pools that dry out seasonally. Males are prized in the aquarium hobby for their intense coloration, while females are plain by comparison. Like other Nothobranchius species, the redtail notho completes its entire life cycle -- hatching, growing, and reproducing -- within the few months that its pool holds water, then leaves behind drought-resistant eggs buried in the mud. It is a common reference species in killifish taxonomy and in aging research due to its naturally short lifespan.

Adult redtail nothos are small and torpedo-shaped, reaching only 4-6 cm.

• Body: slender, laterally compressed, with a slightly upturned mouth typical of surface-feeding killifish
• Male coloration: blue-green flanks with scattered red-orange spots; caudal fin bright red bordered by a black band
• Female coloration: plain olive-gray with translucent, rounded fins
• Fins: rounded dorsal and anal fins set far back near the tail

Look-alikes include other Nothobranchius species such as N. rachovii, which shows a more blue-tinted tail with a red central band rather than an all-red tail; precise identification often requires knowing the collection locality.

Redtail nothos inhabit shallow, temporary freshwater pools and marshy depressions that form during East Africa's rainy season on Zanzibar Island and the adjacent Tanzanian coast. These pools are typically warm, soft, and slightly acidic to neutral, with a muddy substrate that the fish use for egg deposition. Because the habitat dries completely for months at a time, the species has no permanent aquatic range -- populations exist only as embryos buried in dried mud until rain refills the pools. This boom-and-bust habitat cycle restricts the species to lowland coastal savanna and floodplain terrain rather than rivers, lakes, or the ocean.

Redtail nothos are active, fast-growing fish that mature within weeks of hatching, driven by the short lifespan of their seasonal pools. They are substrate spawners: pairs repeatedly dive into soft mud or leaf litter to deposit and fertilize single eggs, which then enter diapause and can withstand months of desiccation. Adults feed opportunistically near the surface and midwater on mosquito larvae, small crustaceans, and other zooplankton, foraging almost constantly to fuel rapid growth. Males display and spar for spawning access to females, establishing loose, short-lived territories around favored substrate. The entire population dies when the pool dries, leaving only buried eggs to restart the cycle when rains return.