Australian Rainbowfish Breeding Guide

How to breed the Australian rainbowfish (Melanotaenia fluviatilis): sexing, spawning over plants or mops across days, and raising surface-feeding fry.

Overview

The Australian (Murray River) rainbowfish, Melanotaenia fluviatilis, is a hardy egg-scattering fish from the Murray-Darling basin of southeastern Australia, reaching about 10 cm. It spawns over fine-leaved plants or spawning mops, laying batches of adhesive eggs over an extended period, which makes it relatively straightforward to breed.

Sexing

Males are larger and more colourful, developing a characteristic high back as they mature; breeding males intensify in colour, with red spots and blackish fin margins on the dorsal, anal and caudal fins. Females are less intensely coloured with plainer fins.

Conditioning

Keep the fish in a group of at least six and condition them on a varied diet. Well-conditioned, brightly coloured males display vigorously to ripe females ahead of spawning.

Breeding Setup

Use a spawning tank of at least about 75 cm with fine-leaved plants such as java moss or spawning mops as an egg substrate. Slightly hard water around pH 7.5 and a spawning temperature near 22-24 C (about 72-75 F) suit the species; spawning is seasonal in the wild, generally occurring once water exceeds 20 C.

Spawning Behavior & Trigger

The pair spawns over a period of several weeks, laying small batches of eggs each day; reported fecundity averages around 130 eggs (range roughly 35-333), in small daily batches over several days. The eggs sink into the plants or mop and attach by fine adhesive threads.

Egg & Fry Care

The eggs hatch in roughly 6-10 days depending on temperature. Newly hatched fry are very small and stay near the surface, so they need infusoria-type foods at first, progressing to brine shrimp nauplii after about a week; sinking foods are unsuitable because the fry remain near the top.

Common Challenges

Because eggs are laid continuously over days, the mop or plants are often removed and incubated separately to protect the eggs and fry from being eaten. The tiny, surface-oriented fry also require very fine first foods, which is the main rearing hurdle.