Guenther's Nothobranchius (Nothobranchius guentheri) Breeding Guide

Breeding the classic Zanzibari annual killifish Nothobranchius guentheri: peat spawning, an 8-12 week dry incubation, and CO2-triggered hatching.

Overview

Nothobranchius guentheri is an annual killifish endemic to Zanzibar, where it inhabits intermittent rivers and seasonal freshwater marshes that dry up each year. It has been kept in the hobby for over a century. In the wild it feeds on mosquito larvae and other planktonic creatures, and its eggs persist in the substrate after the adults die when their pools evaporate.

Sexing

Males show iridescent blue scales with brick-red unpaired fins, while females are smaller and a uniform grey-brown. The strong dimorphism makes pairing simple; keep one male with several females.

Conditioning

As a carnivore it should be conditioned on small live and frozen foods including mosquito larvae, daphnia and bloodworm. Heavy feeding keeps females spawning daily over the peat.

Breeding Setup

Provide a small species tank with a container of soft peat for the fish to spawn into. The peat spawner habit means pairs repeatedly push into the substrate to bury eggs. Gentle filtration and low light keep the group settled and productive.

Spawning Behavior & Trigger

Pairs or small groups spawn by repeatedly pushing into the substrate and releasing and fertilising a single egg at a time. After spawning the peat is collected and gently squeezed to a damp consistency before storage.

Egg Diapause & Hatching

Specially adapted chorion proteins retain moisture in the eggshell, allowing the eggs to survive the dry season. Eggs have a dry incubation of between 8 and 12 weeks, with most hatching after about 9 weeks. When water returns, the fry detect the pressure change of submersion and a rise in dissolved carbon dioxide, which triggers release of the enzyme chorionase to soften the shell for hatching. Flood the damp peat with soft, cool water to hatch a batch.

Common Challenges

If the incubation period or moisture is off, eggs may not respond to the first wetting; re-drying the peat and wetting again often recovers them. Weak fry that cannot leave the bottom, known as belly-sliders, indicate over-rapid or poorly timed hatching.