Not many fish have a miniature alternative, but Rasbosoma spilocerca is the perfect minature version of the sizeable scissortail rasbora. Alex takes a closer look at this nano fish that's well suited to planted aquariums.
A shimmer of silver along the flanks and a striking banded tail. The scissortail rasbora (Rasbora trilineata) is certainly an eye catching fish, filling aquariums with plenty of activity. But, they also reach 15cm (6") in length, and with their fast swimming nature, you'd need tanks of at least 120cm (48") long to house them properly.
A large shoal of scissortail rasbora (Rasbora trilineata) looks amazing but requires a large tank - Photo by Shutterstock
Plenty of fishkeepers aren't able to fit aquariums of this size in their homes; so this striking species remains just out of reach. What if there was a smaller version, one well suited to smaller aquariums filled with vibrant aquatic plants? Well, fortunately for us, Rasbosoma spilocerca is just that.
Introducing the Dwarf Scissortail Rasbora
Rasbosoma spilocerca is a rare find in the hobby, I had certainly not encountered it in the flesh for many years. Commonly known as the dwarf scissortail rasbora, I saw a lovely group when visiting Wirral Aquatics for a Retailer Focus feature (which is in the July 2026 issue).
They are the sole member of the genus Rasbosoma, having previously been placed within Rasbora, which the larger scissortail still belongs to. The dwarf scissortail rasbora reaches just 3cm (1.2") in length and has a slender, translucent body with a subtle silver sheen. The tail bears the characteristic black-and-white markings that give scissortail rasboras their name, though in a far more delicate form.
In fact, they are so similar to the larger scissortail that they were once thought to be juveniles of that species.
Indeed, both species come from the lower Mekong River across Laos, Thailand and Cambodia, although the larger scissortail has a wider distribution which reaches into Malaysia, Sumatra and Borneo.
Dwarf Scissortail Rasbora Fact File
Scientific name: Rasbosoma spilocerca
Size: Up to 3cm (1.2")
Origin: The lower Mekong River, in Thailand, Laos and Cambodia.
Habitat: Occurs in shallow, slow moving water, inhabiting swamps, marshes and flooded grasslands. They are often found in areas with dense aquatic plants and clear water.
Tank size: 45x30x30cm (18x12x12").
Water requirements: Near neutral water works great for this species, avoiding the extremes. A slightly acidic pH is best, but between 6 and 7.5 will suffice, along with a hardness below 10°H.
Temperature: 22-26°C (72-79°F).
Temperament: Best maintained in a species only tank or alongside other small peaceful species, for example chilli rasboras, as they are easily outcompeted. Maintain them in groups of at least eight individuals as they require plenty of conspecifics to thrive.
Feeding: A micropredator that will readily snatch prey items from the water. In aquariums they readily adapt to prepared foods, but small live and frozen foods should be offered on occasion, with Cyclops, Daphnia and baby brine shrimp (Artemia spp.) all being great options.
Availability & cost: A rare gem to encounter, they were marked up at £3.45 each, or 5 for £16 at Wirral Aquatics.
Caring for the Dwarf Scissortail
While the larger scissortail rasbora requires tanks of 120cm (48") to thrive, their dwarf relatives will do well in just 45cm (18"). Although, I'd probably stretch to a 60cm (24") tank so that I could keep a larger group if I were to ever house them at home.
Water chemistry wise, they are actually quite undemanding. Slightly acidic to near neutral will work great, matching the parameters of their native waters. Indeed there are reports of them successfully breeding in water with a pH of 7.
However, that doesn't make them hardy, as such. They will not appreciate the swings in water parameters of an immature tank. A well-established aquarium with an efficient, but gentle, filter will be required for them to thrive. You'll also need to ensure you have a tight-fitting lid, as like with many rasboras, they may dart up and out of the aquarium when startled.
Aquascaping for Rasboras
To know how best to set up an aquarium for the dwarf scissortail rasbora, we need to look at their native habitats. They typically live in sluggish areas filled with aquatic plants, clear water, and with areas of shade provided by marginal and emergent plants.
To achieve this we need to start from the bottom. A nutrient rich substrate will give you the best medium to grow a range of live plants in. This can be in the form of a compost or nutrient rich base layer covered in a fine sand, or a specifically designed plant soil. Indeed, the dark colouration of the latter can help to accentuate the subtle colours and beauty of this little rasbora.
A dark nutrient rich substrate would be an ideal choice for this sort of display - Photo by Shutterstock
They won't be well suited to the high flow that is present in many high-tech aquascapes, so choose some easier plant species to decorate this tank. Hairgrass (Eleocharis spp.), dwarf lilies (Nymphaea spp.), hornwort (Ceratophyllum demersum) would all help create a biotope feel, but Cryptocoryne, Vallisneria, Java ferns and Anubias would all work nicely too.
Hardscape wise, again they'll be unfussy. Tall branching woods would look effective, providing plenty of height and cover, but I'd avoid any rocks that may raise the pH. I'm picturing a densely planted nature aquarium vibe, not a minimalist Iwagumi, here.
The addition of a handful of floating plants will help provide the shade that the emergent plants do in the wild, helping the rasboras to settle into the aquarium. These could always be removed, once the other plants have established themselves.
What's Next for the Dwarf Scissortail Rasboras
Normally, we might end with a section on breeding this species, but in this instance, I am going to leave it there. That's because I have been thoroughly captivated by this species ever since I spotted them in the shop and I would rather like to keep them in the not too distant future.
I do not know if I will create a loose biotope for them, or attempt to breed them. But, whatever I do, I will return with details of my own experiences keeping them, and hopefully some better photos, in the future.
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