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Maximum size : 2.5 cm

Siamese Dwarf Rasbora - Trigonostigma somphongsi : Complete Fish Profile & Care Guide

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The Siamese Dwarf Rasbora (Trigonostigma somphongsi) is a rare and visually striking species that would make an excellent addition to any aquarium enthusiast's collection. Although these beautiful fish are critically endangered in the wild due to habitat loss, dedicated breeders around the world are working hard to preserve their populations.

To truly appreciate their beauty, it is recommended to keep Siamese Dwarf Rasboras in a school of at least ten individuals in a spacious aquarium. While they are peaceful creatures that can coexist with other small, gentle species, it is best to avoid any potentially aggressive or larger fish that may intimidate or harm them. For this reason, they may thrive best in a tank with only their own species or with Dwarf Shrimp.

When it comes to aquarium setups, a heavily planted layout with a dark substrate is ideal for showcasing their vivid colouration. Including driftwood roots or branches for natural hiding places, caves, and shaded areas will provide a sense of security and a more authentic environment for these fish. Adding dried leaves, such as oak, beech or almond, will further enhance the natural feel, as the decomposition of these leaves will promote the growth of beneficial microbe colonies and release chemicals and tannins that simulate blackwater conditions and provide a secondary food source for babies.

To best appreciate their elongated transparent bodies, it is best to keep Siamese Dwarf Rasboras in reasonably dim lighting. Floating vegetation can help diffuse the illumination, creating a more comfortable environment for these fish. In well-conditioned individuals, their transparent bodies display a stunning orange hue, while their thick black stripe grows broader towards the anterior. Their fins are generally transparent, except for their caudal fin, which can be orange in colour.

By providing a suitable environment and diet, aquarium enthusiasts can help preserve and enjoy the rare beauty of the Siamese Dwarf Rasbora.

Siamese Dwarf Rasbora Photos

Sexual Dimorphism

Distinguishing between male and female Siamese Dwarf Rasboras is a task that can be accomplished with relative ease. Typically, sexually mature females display a deeper body structure, larger size, and a silvery-yellow hue. Conversely, males are generally slimmer, slightly smaller, and develop a beautiful copper-orange colouration once they have acclimated to the aquarium environment.

Quick Facts

Scientific NameTrigonostigma somphongsi
Year Described1958
Other NamesSomphongs's Rasbora
Max Size2.5 cm
Aquarium LevelMiddle - Top
DifficultyBeginner - Intermediate
Best kept asGroups 10+
LifespanUp to 4 Years

Water Parameters

Water TypeFreshwater
PH5.0 - 7.0
GH2 - 10
TDS18 -143
71 - 79
21 - 26

Natural Habitat

Siamese Dwarf Rasboras are found exclusively in the Mae Klong Basin near Ratchaburi province in Western Thailand. These tiny treasures were once thought to be extinct, but they have recently been rediscovered, and their beauty continues to fascinate aquarium enthusiasts around the world. Submerged aquatic plants grow thickly in the streams and tributaries in their natural habitat, creating a lush and vibrant environment. The water can sometimes appear brown due to tannins and other chemicals released by decomposing organic matter. Fallen leaves, branches, and twigs litter the substrate, providing shelter for the fish and other aquatic life. The dense vegetation and forest canopy above these streams filter out most of the sunlight, resulting in dimly lit environments with soft, slightly acidic to neutral water - the perfect conditions for these exquisite creatures to thrive.


Siamese Dwarf Rasboras are fascinating little fish that use a unique spawning method. Unlike most fish that scatter their eggs, Siamese Dwarf Rasboras attach their eggs to the underside of broad plant leaves. If your fish are in good condition, they will often spawn, and in a densely planted, established aquarium, small numbers of young may start to appear without any intervention. However, if you would like to increase the number of fry, a more controlled approach is necessary.

To begin, you should condition the adult group together by feeding them small amounts of live and frozen food 2-3 times a day for a couple of weeks before attempting to spawn them. Once the females are full of eggs and the males are displaying their best colours, perform a significant, cool water change and then place one or two pairs into a breeding tank. The breeding tank should be dimly lit, and the bottom should either be left bare or covered with mesh that allows eggs to fall through but is small enough to keep adults from reaching them. Artificial grass matting can also work just as well. The breeding tank's pH level should be between 5.0 and 6.0, and the temperature should be slightly higher than the regular aquarium. You should also add good-sized broad-leaved plants such as Microsorium and Cryptocoryne. Filtration is unnecessary unless you prefer to add a small air-powered sponge filter.

Spawning typically occurs early in the morning and is led by a spurt of courtship activity by the males. After several "dry runs" over a chosen spawning site, the female begins to lay small batches of eggs, which the male fertilises before the next set is laid. If the couple fails to spawn straight away, you can leave them where they are. However, if you do not notice any eggs after 3-4 days, return them to their usual aquarium and choose another pair. Once all the eggs have been laid, you will need to remove the adults from the breeding tank as soon as possible, or they will consume the eggs if given a chance. The incubation period is temperature-dependent, but the eggs will typically hatch somewhere between 24-48 hours later, with the young becoming free-swimming about a week after that.

To feed your fry, begin with Paramecium or a similar food and move on to baby brine shrimp and microworm once they are large enough to accept them. Again, providing a nutrient-rich diet is essential to ensure optimal health.

Diet & feeding

Siamese Dwarf Rasboras are an uncomplicated species to feed as they are not discerning eaters. To ensure your fish remains healthy and displays their best colours, it is advisable to provide them with regular helpings of small live and frozen foods such as daphnia, brine shrimp, cyclops and bloodworm. Alongside this, it is essential to offer high-quality dried foods such as crushed flakes, micropellets, and granules to balance their diet.


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