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by Ola Åhlander

 

Previously Rasbora:

Genus Trigonostigma Kottelat & Witte 1999

Family Cyprinidae, subfamily Rasborinae

Trigonostigma; from trigonon, triangle, "hatchet" and stigma, brand, spot.

 

 

Introduction

The type species of this genus, Trigonostigma heteromorpha, the harlequin rasbora, must be considered to be one of the most classical aquarium fishes. It was described 1904 as Rasbora heteromorpha, and was imported to Europe as early as 1906. It became already from the beginning a very popular aquariumfish with its beautiful colours , a position it has held to today. The remaining three species in the genus was described by Meinken during the 1950´s and 60´s, all of them as Rasbora. What many ichthyologists and interested aquarists already had suspected was confirmed when Kottelat & Witte 1999 gathered these fishes in an own genus, Trigonostigma. Besides the similar appearance, which differ from the remaining Rasbora-species, these fishes have the special breeding behaviour in common. A beautiful example how aquarists by study the fishes and publish their observations of the fishes behaviour, may help the ichthyologists.

 

 

These small fishes originate from south-east Asia, where they live in soft and slightly acidic water, often in so-called peatswamps. The spawning takes place in the flooded areas when the water level raises during the rain period. Even if none of these species are considered to be threatened, their environment is. The tropical peatswamps of Asia is one of the most species-rich biotopes in the world, but they decrease rapidly due to forestry and agricultural trenching.

 

In the aquariumbooks and on the internet there is of course a lot to read about these fishes, mainly about the harlequin rasbora. Unfortunately there is a severe confusion of the species T. hengeli and T.espei, and how to separate them from one another. Often is only one of the species mentioned, and its seems to be some kind of a lottery which name that is used. Actually, they are not to difficult to distinguish from one another, at least not adult, fully coloured animals. I hope that the pictures below is good and clear enough to show the difference between the two. 

 

The fishes

 

Trigonostigma espei (Meinken 1967)

Origin: The Mekong river basin; Cambodia, eastern Thailand, maybe also in southern Laos.

Size: approx. 3-4 cm

 

Trigonostigma espei

 

Trigonostigma hengeli (Meinken 1956)

  Origin: Sumatra and Borneo.

Size: approx. 3-4 cm

Trigonostigma hengeli

 

Trigonostigma heteromorpha (Duncker 1904)

  Origin: The Malay peninsula and Sumatra.

Size: approx. 4-5 cm

 

Trigonostigma heteromorpha

"Black" harlequin, an artificial bred morph.

 

Trigonostigma somphongsi (Meinken 1958)

  Origin: Mae khlong river basin, Thailand.

Size: approx. 2,5 cm

The smallest species of the genus. Unfortunately I do not have any picture of this fish, it seem to be very rare and difficult to find. (At least in Swedish aquariumfish stores.) There is a good picture of it in the Aquarium atlas vol. 3, and consequently in volume 1-5, "the index". The ground colour is yellowish, with a black stripe from the tail to the middle of the body. T. somphongsi lack the in the other species conspicuous hatchet-marking on the side, the stripe is only slightly wider posteriorly.

 

The spawning is like in the other species, the eggs are attached on leaves.

Since I not have had the opportunity to keep this species myself, I can not be sure that the following text is valid for it too. But according to the literature I have at hand, there shall not be any major differences in either care and feeding or breeding.

 

 

Care and feeding

The Trigonostigma species are small peaceful, hardy and colourful fishes, ideal for the community aquarium. Due to their size, they may not demand that much space, but are at their best in a larger tank in schools of ten or more. A proper school in a large aquarium is a stunning sight, fully comparable in display of colour with both neon and cardinaltetras. Plants do much for the fishes to thrive, a well planted surrounding provides both hide and spawning places.

 

They have no major demands at the water except maybe when breeding, they prefer soft and slightly acidic water. Appropriate water measurements could be: Temp. 23-27º C, pH 6-7,5, KH <5. Consider this as guidelines, these are hardy fishes and in most places they do well with ordinary tap water. A normal aquarium care with regular water changes is good enough to keep these fishes in a good condition.

Since these are small fishes, the food must of course be of suitable size. A high quality flakefood is O.K. for maintenance, but to get the fishes in spawning condition it seem to take live or frozen food at proper size.Cyclops, daphnia and mosquito larvae is highly appreciated. Go outside with the hand-net to pools and ditches!

 

In this tank has about twenty or so T. espei grown up. Eggs and fry managed, even though there besides the parents lives a couple of pearl gourami, Trichogaster leeri, some shrimps, Caridina sp. and Siamese algae-eaters, Crossocheilus oblongus, in the same aquarium.

 

Breeding

Hard to breed?: For many aquarists breeding is the primary goal of the hobby, the final proof that they have managed to care for the animals as good as possible. An attempt to breed the Trigonostigma-species may not be for the beginner, but it is well worth a try for any aquarist with a little experience of aquarium fish breeding .

 

There are different opinions if these fishes are hard to breed or not. Some authors consider them very difficult to raise fry from, others state that it is quite easy. I am of the latter opinion myself..I have even got surviving fry of T. espei in my community tank. It is a well planted aquarium with not to much fish in it, but still. The difficulties is often said to be to find a matching breeding pair. I myself believe that this is because too young animals has been used in the breeding attempts, it seems that these fishes reach sexual maturity later than other fish-species at the same range of size.

Below I describe how to breed these fishes. It is my own experiences, and there is probably many other ways to succeed.

 

Spawning behaviour: One of the reasons that these four species is placed in an own genus is the special breeding behaviour. When spawning, the female attaches the eggs on leaves, often on the downside, and the male comes after to fertilise it. This is repeated several times until the spawning is over. There is a intensive courtship from the male before the spawning, and the breeding couple do numerous "test-spawns" when no eggs are laid. This can go on for hours before the actual spawning takes place.

 

Sexual differences: If you shall try to breed your fishes, you must of course know that you have at least one fish of each sex. The sexes are quite similar, but there are some differences. "The hatchet" are more marked at the male and are more pointed downwards, the marking are more rounded in the female. This is valid of course only in T. espei, T. hengeli and T. heteromorpha. A mature female is also often somewhat larger than the male, and has a  conspicuously more rounded body. This is easy to see from above.

 

Breeding preparations: I use a well cleaned 60 litres aquarium, bare glass bottom. I have a net on the bottom that I stick some Hygrophila polysperma in, which makes a good spawning substrate. I use the net to if possible save the eggs that don´t attach properly and falls to the bottom. Cryptocoryne sp. is often recommended as spawning plant, but any plant will do which has leaves broad enough. One could probably use plastic plants too, I have not tried that.

I use my regular tap water, which is a very soft water, KH 1-2. If you have a harder water, I believe that you are forced to mix it with distilled or R.O. water to a hardness of KH 5-6 at the most. I leave the water aerating for a day or two. Some peat may make the water more of a rainforest-water, but it is not necessary. Avoid extreme water measurements, there is no need for such. I have had some nice broods with nothing added at all to the water. I use an air-driven foamfilter, Tetra billifilter, for filtering and aeration. 

 

The breeding couple: Unlike most tetras for instance, it seems to me that the best breeding specimens in the Trigonostigma-species is older fishes, from about a year and up. The best and easiest way to select a breeding pair is to let the fishes go in a school in a community tank and feed them two, three times a day with frozen or (preferably) live food for a couple of weeks before the breeding attempt. If one does a big water change, up to 50 %, almost certain some of the fishes will begin with the courtship. Move a pair of these to the breeding aquarium, where they will spawn, probably the morning after. If they don´t spawn in three-four days there is no use to proceed, they will not breed. Do not feed the fishes in the breeding tank!

 

 

A couple of  T. espei spawning. The female attaches the eggs to a leaf, and the male waits to fertilise them.

After the spawning: As soon as the pair has finished the spawning they should be transferred back to the community tank, they are often severe egg-eaters. I have seen a female lay the eggs, turn around, and quick as a lightning swim down and eat the eggs that did not attached properly, before they sink under the bottom-net. Eggs that is attached properly to the leaves is usually  left in peace as long as the spawning proceeds. I diminish the light in the aquarium after the spawning to get a better hatching, but I do not use any anti-bacterial substances or such. The eggs hatch after about 24 hours, but the fry is not free swimming until after a week. One can see the fry "hanging" on leaves and on the aquarium glass.Do not feed the fry until they swim properly. Any such food will only foul the water, and increase the risk for bacterial or fungus infections on the fry.

 

Raising the young: To raise the fry is usually no problem, start with newly hatched brine shrimp (artemia). I also give them some infusoria-solution like "liquifry" or similar the first days, but I am not sure if this really is necessary. If the fry makes it the first week, there is no big problems left, under the circumstance that you can give them the proper food. Microworms is a good supplement the first month, by the way. Try with frozen bosmids or cyclops after three to four weeks, if the fishes eats it you may stop with the brine shrimp. I have seen frozen moina in the stores, which probably also could be given quite early. Of course is it important to keep a good water quality, regular water changes makes the fishes thrive and grow faster. After four to five weeks the black stripe and the red or yellow colour start to appear, then it is time to be seriously delighted of a successful breeding..

 

At last

This is popular fishes which are kept in any major aquarium store, at least the harlequin rasbora. With their strong colours the look good in any aquarium, and if you have a school, why not try to breed them? It is not that difficult, and to have a home-grown school of these beautiful fishes should be of great joy to any aquarist.