Trigonostigma Heteromorpha (Harlequin Rasbora)

Aquarium Livestock
1 Nov 14:43

Harlequin Rasbora

Common names: Harlequin Rasbora

Scientific name: Trigonostigma Heteromorpha


A really great, classic community fish species. This little darling looks beautiful when in a peaceful aquarium in a shoal of 6-10 fish. The black triangle is the most obvious pattern on the fish, but the bronze glow surrounding it is what makes them really shine.

As with many fish, small individuals seen in shops may not always look too special, but with some good food and a bit of size they will soon look great. However, do look for good body shape and avoid specimens that appear stunted. Wild specimens and European tank bred ones are often particularly bright.

Sexing:  Males display brighter, more intense colours, Females are obviously rounder in the body and may be a bit bigger.

Size: 4cm.

Where are they from?: Harleqin Rasboras are widespread in South-East Asia, found in Thailand, Singapore, Borneo, Sumatra and peninsular Malaysia.

Their natural habitats are slow flowing, slightly acidic rivers with lots of vegetation.

Aquarium size: Minimum 60cm x 30cm x 30cm.

Aquarium conditions: These little fish are very easy to keep, almost a domesticated species these days. They can be kept in many different areas successfully – including hard water areas, however, if possible keep them in slightly acidic conditions.

It is important to provide gentle water flow – they will not do well in torrents. Keep them in peaceful tanks with other species with similar needs. They do well with small Tetras, smaller species of Gourami and smaller Barbs. They should be kept in groups of 6-10 individuals.


Harlequin Rasboras are a bit trickier than some to spawn and they do it slightly differently too! They are best spawned in a separate breeding aquarium, set up specifically for this purpose. When spawning they do a kind of barrel roll and lay their eggs on the underside of leaves in order to protect them.

Rasboras do need to be well conditioned prior to spawning. Separate the sexes and feed them with a variety of good quality foods until the female appears full of eggs and the males are displaying to each other. Then, place a pair into the spawning aquarium, which should be furnished with some broad leaved plants – pots of Cryptocoryne sp. work well.

Spawning usually occurs in the morning. You must remove the parents afterwards. The eggs should hatch in 48 hours (quicker at higher temps, longer at lower temps). The babies will then feed off their yolks until they become free swimming (usually about 3-5 days).

Final comments/Key points

  • This species was first imported in the early 1900’s so really is a classic aquarium fish.
  • They are available in several colour forms including gold and black/purple
  • Three other species are in this genus T.espei, T.hengeli and T.somphongsi. The first 2 are fairly commonly available in the hobby.


Author & Photo credit - Parkers Manager Patrick Davies.