Rachov's Nothobranch Breeding Guide

How to breed Nothobranchius rachovii, an annual killifish: sexing, peat-substrate spawning, 5-7 month egg diapause in damp peat and wet-hatching fast-growing fry.

Overview

Nothobranchius rachovii is an annual killifish from the floodplains of the lower Zambezi and the Pungwe River in Mozambique, where it lives in flat plains or water depressions that dry up annually. When its habitats become desiccated during the dry season the adult fish die, leaving fertilised eggs encased within the substrate. Typical aquarium lifespan is only 6-12 months, and fish mature in about twelve weeks.

Sexing

Males grow larger and are far more colourful than females, which are more neutrally coloured. Maximum size is around 50-55 mm. Several colour forms exist, including a darker KNP Black form and a Red variety with red heads and turquoise highlights, but all females remain plain.

Conditioning

Feed adults small live or frozen foods such as Daphnia, Artemia and bloodworm to bring them into spawning condition. Maintain breeders at 20-24 C, pH 6.0-7.5 and hardness 54-179 ppm. The species does not require peat for general maintenance, only as a spawning substrate.

Breeding Setup

Peat moss is used as the spawning medium, mimicking the soft bottom of the natural pools. As a bottom-diving annual, the pair drives down into the peat to deposit eggs, which are then collected with the peat for dry incubation.

Spawning Behavior & Trigger

In nature the fish bury their eggs in the mud as the water level decreases, which preserves them until the rains return; the eggs develop while buried and hatch once the pools refill. In the aquarium this is reproduced by collecting the egg-laden peat and storing it damp rather than submerged.

Egg Diapause & Hatching

The eggs are drought-resistant and enter diapause within the substrate. They should be stored at 21.1-25 C (70-77 F) for 5-7 months before being wetted, after which the fry hatch and grow very quickly, reaching sexual maturity at around 3 weeks of age. If the eggs do not hatch on first wetting, the peat is re-dried and stored for a further period before another attempt.

Common Challenges

Getting the diapause duration and storage temperature right is the central difficulty: wetting too early gives few or no fry, and embryos at different developmental stages may need repeated dry-and-wet cycles. The short adult lifespan also means breeding must be timed within the fish's brief reproductive window.