Truncata Rasbora (Trigonostigma truncata) Breeding Guide

Trigonostigma truncata is a harlequin relative that, like its genus, attaches eggs to the underside of broad leaves rather than scattering them.

Overview

Trigonostigma truncata is a harlequin rasbora described by Tan in 2020 from coastal swamp forests of the Malay Peninsula, distinguished from the common harlequin (T. heteromorpha) by its truncated black wedge marking, orange-red anal fin and shallower body. Detailed species-specific breeding accounts are scarce, so the guidance below follows the well-documented breeding pattern shared across the genus Trigonostigma.

Sexing

Within Trigonostigma, sexes are separated by the shape of the dark wedge-shaped flank marking: in males it shows a sharper, more well-defined outline, whereas in females it has a more rounded appearance. Mature females are also typically rounder-bellied.

Conditioning

For Trigonostigma, the recommended method is to feed small amounts of live and frozen foods two or three times a day in the weeks leading up to a spawning attempt, until females are full of eggs and males show their best colours.

Breeding Setup

A separate, dimly lit spawning tank containing broad-leaved plants is used so that the pair has suitable leaf undersides to deposit eggs upon, consistent with the genus pattern.

Spawning Behavior & Trigger

Across the genus, spawning is triggered by a large (40-50% of tank volume) cool water change, after which one or two pairs are introduced. Unlike scatterers, Trigonostigma pairs perform dry runs over a chosen surface and then attach eggs to the underside of a broad leaf, often spawning in an inverted position.

Egg & Fry Care

Following the genus pattern, eggs hatch in about 24 to 48 hours with fry free-swimming in around a week. First foods are Paramecium, progressing to Artemia nauplii and microworm as the fry grow.

Common Challenges

The leaf-attaching spawning mode requires healthy broad-leaved plants and soft, acidic water; because species-specific data for T. truncata is limited, the genus-typical protocol should be applied and verified against the fish's own behaviour.