Trigonostigma truncata

Trigonostigma truncata is very similar to the Harlequin Rasbora. However, they are slightly smaller and have a light blue stripe above their axe.

Trigonostigma truncata

Trigonostigma truncata was described in 2020 by Tan. The genus name Trigonostigma can be broken down into three ancient Greek words. “Tres” or “Tria” means three, “gonias” means angle and “stigma” means signal. The species name truncata is derived from the Latin ‘truncus’ which means cut off. This is a reference to the axe-shaped triangle on the flank. The tip of the ax does not reach the caudal peduncle.

The species has been available in the aquarium hobby for some time without our knowledge. They were mixed with Trigonostigma heteromorpha at the capture stations as being one species. They are now also for sale under their own name.


Trigonostigma truncata is most similar to Trigonostigma heteromorpha. However, the overall body shape is slightly less high and Trigonostigma truncata appears slightly smaller with a maximum total length of about 3.5 to 4.5 centimetres.

The ground colour is orange/red. The belly is lighter in colour to silver. Depending on the light and mood of the fish, the front half of the fish may show a faint blue reflective colour. Under aquarium lighting and fully coloured the flank can give a purplish reflective colour.

A black axe is visible on the flank. The front edge is straight and the tip of the axe runs backwards but stops in front of the caudal peduncle. Where the tip of the axe stops, a bright orange spot is visible on the caudal peduncle. When the fish are properly coloured, a light blue iridescent stripe will be visible just above the axe.

Trigonostigma heteromorpha has a black stripe just behind the gill cover. This line is completely absent in Trigonostigma truncata.

The paired fins (pectoral and pelvic fins) are transparent. The dorsal, anal and caudal fin show an orange-red colour.


Trigonostigma truncata can be found along the east coast of Malaysia and southern Thailand. They inhabit the acidic freshwater swamps in the forests. These usually end up in rivers.


Trigonostigma truncata is an omnivore. Their diet should therefore consist of both animal and vegetable food. Give them a varied diet of, for example, live and frozen food such as brine shrimp, Mysis, tubifex, mosquito larvae, etc. You can also feed them with flake food for omnivores, spirulina flakes and, for example, small granules. They are quite small fish, so keep in mind that the food does fit in their mouth.

The Aquarium

An aquarium for a school of Trigonostigma truncata should be at least 60 centimetres long. Keep a group of at least six pieces, but preferably even more. It goes without saying that a larger school also needs a larger aquarium.

Set up the aquarium with lots of plants for the fish to hide in. Leave some swimming space at the front so that the fish can come to the front of the aquarium where you can see them.

Trigonostigma truncata likes a little bit of current and a bit acidic to neutral water. A pH of 5 to 7 and a temperature of about 24 to 27 degrees Celsius works fine. You can optionally filter the water over peat. The water then acidifies slightly and gives the water a somewhat darker colour.

Breeding Trigonostigma truncata

I have not been able to find anything about breedingTrigonostigma truncata. The species has only recently been officially described. Presumably, the reproduction takes place as in Trigonostigma heteromorpha.



John de Lange

Copyright images


Trigonostigma truncata, a new species of harlequin rasbora from Malay Peninsula

Additional information





First described by

Heok Hui Tan


Min. aquarium length in cm






Minimum length


Length maximum



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