Breeding Harlequin Rasbora
How to breed Harlequin Rasbora (Trigonostigma heteromorpha): sexing, soft acidic spawning water, eggs laid under broad leaves, and fry care.
Overview
Harlequin Rasbora (Trigonostigma heteromorpha) is of intermediate breeding difficulty and spawns differently from typical scattering rasboras: the pair deposits eggs on the undersides of broad plant leaves. Success depends strongly on soft, acidic water.
Sexing
Females are usually rounder-bellied and often a little larger than the slimmer, more colourful males. The dark wedge marking also differs: in males it has a sharper, more well-defined outline, whereas in females it appears rounded.
Conditioning the Breeders
Feed small amounts of live and frozen foods two or three times a day in the weeks leading up to a spawning attempt. Introduce pairs when the females look full of eggs and the males show their best colours.
Breeding Setup
- Very dimly lit container with a bare base or mesh so eggs pass out of the adults' reach
- A decent-sized clump of broad-leaved plants such as Microsorum or Cryptocoryne, or an artificial alternative
- Soft, acidic water: pH 5.0-6.0 and 1-5 °H
- Temperature towards the upper end of the 22-28 °C range
- An optional small air-powered sponge filter
Spawning Behavior & Trigger
Spawning usually occurs in the morning. The female swims in an inverted position beneath a chosen leaf and the male curls his tail around her as eggs and sperm are released. Six to twelve eggs are attached to the leaf underside with each embrace; a well-conditioned female may produce up to 300 eggs, though 80 to 100 is more typical. The fish will not spawn in hard, alkaline water.
Egg & Fry Care
Eggs take about 18 hours to hatch at 28 °C (incubation generally 24-48 hours). Fry remain attached to the leaf for a further 12 to 24 hours while absorbing the yolk sac, then become free-swimming in around a week. Offer Paramecium or other infusoria-grade food for seven to 14 days, progressing to Artemia nauplii and microworm. Full adult colour develops over about eight to ten weeks.
Common Challenges
The chief obstacle is water chemistry: spawning is unlikely unless the water is soft and acidic (around pH 6.4, hardness no higher than 4 °dH). Dim lighting and broad-leaved plants for egg deposition are also important, and the very small fry require fine first foods.