Malayan harlequin rasbora

Trigonostigma truncata

Also known as Truncata harlequin

FreshwaterFish

Care at a glance

Temperature: 72–81°F (22–27°C)
pH: 5.0–7.0
Adult size: 1.2 in (3 cm)
Minimum tank: 14 gal (54 L)
Temperament: Peaceful
Social behavior: Schooling
Swim level: Middle
Difficulty: Easy
Breeding: Medium
Rarity: Rare
Origin: East coast drainages of the Malay Peninsula
Family: Danionidae

Overview

This is a harlequin in every practical way, so the familiar care applies: keep a school of eight or more, feed readily accepted small foods, and house it in a gentle, planted community. It is easy and peaceful, sitting in midwater and pairing well with other calm soft-water fish. Offer crushed flake, micro pellets, and frozen daphnia, cyclops, and baby brine shrimp. Check the black wedge on its side and you will know which harlequin you actually own. A planted tank of around 54 liters suits a group.

In the wild

The Malayan harlequin lives in gentle, often tannin-stained streams along the east coast of the Malay Peninsula, in soft, acidic, plant-rich water. Recreate that with a planted tank, a dark substrate, leaf litter or botanicals to tint the water, and calm filtration. Hold it at 22 to 27 degrees Celsius with a pH of 5.0 to 7.0.

Good to know

Trigonostigma truncata is a danio-family rasbora, Danionidae, and a small harlequin of around 3 centimeters. Tan described it in 2020, separating the Malayan populations from the classic harlequin; the name truncata refers to its black flank wedge, which is shorter and cut off rather than tapering to a long point. Like other harlequins it lays adhesive eggs, so breeding rates as moderate.

Did you know

Keepers raised this fish for decades as the common harlequin, until a 2020 study measured the black wedge, found it cut short, and named a second species that had been hiding in the trade all along.

Tank mates

Malayan harlequin rasbora is a peaceful, schooling species that keeps to the middle. These picks match on water type, temperature, pH, size and temperament.