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June 22, 2012

Like many families, the genus Rasbora became a catch-all for the Cyprinids of Asia. During the 90’s a few scientists took it upon themselves to start classifying each species in order to accurately tell what fish was closely related to one another. In 1999, Kottelat and Witte began researching the small group Rasbora heteromorpha. The researchers would place four different fish into the new genus Trigonostigma. This was based not only how similar the fishes were in color, but on how uniquely the fishes spawned. The genus was erected from the Greek words trigonon, meaning hatchet or triangle. While the other word, stigma, means spot or brand. Clearly this derives from the large black stripe found on the four fish.

As I just mentioned, these fish have a very unique way of breeding. Unlike most Cyprinids, the females of these fish lay their eggs onto leaves of plants (usually on the underside) as opposed to scattering them across mosses or the substrate. If you wish to breed them, the best way is to use fish of a year or older. Feeding live foods 2-3 times a day before the attempt is a great idea. Once the female appears egg bound, and the male is in full color, you should change about 50% of the aquarium water and replace it with cooler water.

Wait a few hours (evening is preferred) then move the pair into the spawning tank. According to the spawning takes place in the early hours of the morning. The pair can be seen doing ‘dry runs’ over the spawning area. It may take a while, but eventually the female will begin to produce eggs. Once the fish are done, the parents should be moved back into the main tank. After 24-48 hours, the fry will hatch out and should be fed Artemia nauplii.

Though these fish do not need a very large sized tank, one measuring at least 24 inches long and 12 inches wide is ideal. They are all schooling fish and should be kept in larger numbers in order for them to thrive. The best tank for them would be a well-planted aquarium with a slow current. I would recommend a dark substrate and possibly some oak leaves on the bottom. The rest of the plants are up to you!

Trigonostigma heteromorpha “Harlequin Rasbora” is by far one of the most recognizable aquarium pets in any shop. After all, it’s been in the hobby since the early 1900’s. With its red hue, bluish tint, and sideways black “triangle” it quickly became one of the most successful pets in the trade. So why was this? Well, the fish is very adaptable to water conditions. It will thrive in a pH from the low 5’s all the way up to 7.5 or so. Harlequin Rasboras also won’t mind temperatures in the low 70’s or even the low 80’s. There are even a few different color morphs available in the trade now from selective breeding. I’m sure that most of you have at least seen the fish, if not kept it before. Or maybe, you even still have a group of them. With a max size of around 2”, and being a peaceful fish it certainly makes a great community tank member.

Trigonostigma heteromorpha

Trigonostigma heteromorpha "Purple"

In 1967, Meinken described a sub-species out of Thailand that would become known as Rasbora heteromorpha espei. In 1987, Rainboth and Kottelat evaluated the fish and declared them to be a distinct species. Years later it would be placed into what we now know it as, Trigonostigma espei “Porkchop Rasbora”.

Trigonostigma espei

This is, in my opinion, by far the most attractive of the genus, demonstrating a very beautiful red or orange coloration, a thinner “porkchop” style stripe on the side, and a slightly smaller size – reaching about 1.6” on average. One thing that I really thought was interesting about this species is some of the habitats it can be found in. In southern Thailand, it can be found living in limestone sinkholes that are an amazing blue/green color. The pH is often more alkaline around 7.0-7.4. There is often leaf litter piled up on the sides, yet the water remains very clear.

Maybe I’m just spoiled at my job, but to read that my favorite species of the group is rarely imported seems a bit of a far stretch. We often import in Trigonostigma hengeli “Narrow Wedge Rasbora” direct from the waters of the Sunda Islands. I’m sure you’re asking yourself why I love this fish out of the other two. I know it’s not as red as T. espei, or well known as T. heteromorpha, but I guess I just like the subtle beauty the fish offers. It’s also the smallest member of the family. Most Narrow Wedge Rasboras only grow to around 1.2”. I’m sure it probably gets a little bigger in an aquarium, though. Again, it was Meinken who would describe the species back in 1956, and Kottelat and Witte would later change their genus to Trigonostigma.

Trigonostigma hengeli

Sadly the fourth fish, Trigonostigma somphongsi, is exceptionally rare in the hobby. Like many of you know we thrive in the unusual and are doing our best to come up with a batch. Keep your fingers crossed!

Until next week!

Anthony Perry
Sales Manager