Chili Rasbora Breeding Guide

Breeding Boraras brigittae: sexing, continuous daily egg-scattering in moss, soft acidic water, and rearing the minute fry.

Overview

Boraras brigittae is one of the smallest aquarium fishes, with typical specimens measuring 10-20 mm and the largest recorded reaching about 3.1 cm. It is endemic to the blackwater streams and peat-swamp pools of south-west Borneo, Indonesia, and feeds as a micropredator on small insects, worms, crustaceans and other zooplankton. It is an egg-scattering species that shows no parental care: conditioned adults lay relatively small numbers of eggs daily rather than in a single large spawn, and although they will eat some eggs they do not actively hunt them.

Sexing

Females are noticeably rounder-bellied and often larger than males. Males display more attractive colouration, with dominant individuals showing intense red hues.

Breeding Setup

A 10-15 litre dimly lit container works well. Use a bare base with a mesh that lets eggs pass through but blocks the adults, or plastic grass matting, or fill about half the space with java moss. A small air-powered sponge filter is optional. Suitable water is soft and acidic at pH 5.0-6.5 and 1-5 degrees hardness, with the temperature toward the upper end of the range (around 28 C).

Spawning Behavior & Trigger

Introduce two or three well-conditioned pairs per container; spawning typically begins the following morning. Eggs are scattered into the moss or onto the substrate. Remove the adults after about two days to limit egg consumption.

Egg & Fry Care

Eggs hatch within about two days, and the fry live on their yolk sacs for around a further day. First food is Paramecium or other microscopic organisms; after 7-10 days they accept Artemia nauplii and microworm. Delay water changes for one to two weeks to avoid shocking the young.

Common Challenges

The minute size of the fry demands very small first foods, and because spawning is continuous in small batches, a dedicated, undisturbed container gives the best survival.