Betta Trading

Harlequin Rasbora


A Peaceful and Delightful Fish

I grew up with the idea that this delightful fish's scientific name was Rasbora heteromorpha. This used to be correct, with the heteromorpha referring to the fact that this fish is not a typical Rasbora.  Now the name has been changed to Trigonostigma heteromorpha because of the several differences between the Harlequin Rasbora and the other Rasboras.
As well as being called the "Harlequin Rasbora".  It is called the "Rasbora", the "Harlequin" and the "Red Rasbora". 


The Harlequin Rasbora is native to Singapore, Malaysia, Sumatra and parts of Thailand.  It is found in small streams, often ones coming from peat bogs where the water is stained brown with tannins.  The water tends to be soft, acidic and low in total salts.  The Harlequin Rasbora is one of the little fish that can be found in the small ditches in Singapore.

Length and Longvity
I’ve seen reports of Harlequin Rasboras reaching nearly 2 inches (5cm), but nearly all are less than this.  It will live for about 6 years,

Water Conditions

The Harlequin Rasbora is a tropical fish and temperatures of between 21̊ C (70̊ F) and 28̊ C (85̊ F) are suitable.  I recommend a temperature setting of 24̊ C (75̊ F) for a mixed tank containing Harlequin Rasboras.  Although the water in its native habitat tends to be soft, acidic and low in salts, the Harlequin Rasbora is able to adapt to living in a wide range of water conditions, and can live happily in neutral water somewhat harder than it is used to.
Live plants are a very good idea with the Harlequin Rasbora.


The Harlequin Rasbora is very much a schooling fish and a reasonable sized group should be kept.  A school of a dozen Harlequin Rasboras is a beautiful and striking sight.  Although the Harlequin Rasbora is an Asian fish of a different group, its characteristics are similar to many of the small South American tetras.
I would avoid large or very aggressive fish, but the Harlequin Rasbora is an ideal fish for a community tank of small fish.  Suitable companion species for Harlequin Rasboras are Lemon Tetras, Neon Tetras, Black Widow Tetras, Cardinal Tetras, Emperor Tetras, Head and Tail Light Tetras, Glass Bloodfin Tetras, Glowlight Tetras, Guppies, Endlers Guppies, Neon Tetras, Peppered Catfish, Siamese Fighting Fish , White Cloud Mountain Minnows and Zebra Danios.  Note that not all these common companions are compatible with each other.


One of the reasons the Harlequin Rasbora was removed from the Rasbora genus was its breeding behaviour.  The other Rasboras are egg scatterers while the Harlequin Rasbora attaches its eggs to the underside of leaves, turning upside down to do it.
In contrast to the ease of keeping the Harlequin Rasbora, the conditions for breeding need to mimic the natural habitat of this fish fairly well.  A temperature of 28̊C (82̊ F) is suitable.  Soft, acidic water is essential; a ph of 6 with hardness less than 3̊ is alright.  A high level of tannins in the water is also recommended.

Sources and Picture Credits


The picture next to the title is from Aquario Total. There is also an excellent picture of this fish at Fishwise NZ.


Steve Challis


Singapore has issued a stamp featuring the Harlequin Rasbora.