How to Breed Green Kubotai Rasboras: Neon Micro Spawners
The green kubotai rasbora (Microdevario kubotai) is a tiny jewel of neon yellow-green that looks almost fluorescent under good lighting. If you have a thriving school and want to take the next step, this breed green kubotai rasbora guide from Gensou Aquascaping at 5 Everton Park, Singapore, walks you through conditioning, spawning, and raising fry of these micro-sized cyprinids. At barely 2 cm adult length, breeding them demands patience and precision — but the results are deeply rewarding.
Understanding the Species
Microdevario kubotai originates from slow-moving streams in western Thailand and Myanmar, where it inhabits clear, slightly acidic water among leaf litter and submerged roots. Males are slimmer and display more intense green fluorescence than the plumper, paler females. Sexing becomes reliable at around 4-5 months of age, once the fish reach roughly 1.5 cm. A healthy school in a well-planted tank will often spawn spontaneously, though raising the fry requires intervention.
Conditioning Breeders
Separate your six best males and six plumpest females into a dedicated conditioning tank of at least 30 litres. Feed them three to four times daily with live or frozen baby brine shrimp, micro-worms, and crushed high-protein flake. After 10-14 days of heavy feeding, females should appear noticeably rounder when viewed from above. Water temperature during conditioning should sit at 26-27 °C — slightly warmer than their usual comfortable range, simulating the onset of a tropical wet season.
Setting Up the Spawning Tank
Prepare a separate spawning tank of 20-30 litres with aged, soft water. Target pH 6.0-6.5, GH 2-4, and a temperature of 27 °C. Singapore tap water is already soft, so mixing it with a small amount of reverse osmosis water brings you into range with minimal effort. Place a layer of fine-mesh spawning mop or Java moss across the bottom — this catches the tiny eggs and prevents the adults from eating them immediately. Use a mature sponge filter on the gentlest setting for aeration.
Triggering Spawning
Introduce two or three conditioned pairs into the spawning tank in the evening. First light the following morning often triggers activity: males chase females in tight circles, and the female scatters 20-50 non-adhesive eggs among the moss or mop fibres. The eggs are tiny — barely 0.8 mm across — and nearly transparent. Remove the adults immediately after spawning to prevent predation. The entire event usually concludes within two to three hours of first light.
Egg Incubation and Hatching
Eggs hatch in approximately 24-36 hours at 27 °C. Keep the spawning tank dim during incubation, as kubotai eggs are somewhat light-sensitive. Add a few drops of methylene blue to prevent fungal growth on infertile eggs. Newly hatched larvae are almost invisible to the naked eye and remain attached to surfaces by a yolk sac for another 2-3 days. Resist the urge to feed during this stage — the yolk provides all necessary nutrition.
Raising the Fry
Once fry become free-swimming, their first food must be microscopic. Infusoria cultures or commercial liquid fry food are essential for the first 7-10 days. After that, introduce vinegar eels and then freshly hatched brine shrimp nauplii as the fry grow. Growth is slow: expect roughly 5 mm at four weeks and 1 cm at eight weeks. Perform tiny daily water changes of 10% using a turkey baster to avoid sucking up fry, and maintain pristine water quality throughout.
Common Challenges
Egg fungus is the biggest hurdle. Infertile eggs fungus rapidly and can spread to viable ones, so remove any opaque white eggs with a pipette within 12 hours of spawning. Fry mortality in the first week is typically 40-60% even under good conditions — this is normal for micro-species. Low food density is usually the culprit, so ensure your infusoria culture is dense enough that the water appears slightly cloudy. Singapore’s warm ambient temperature actually helps here, as it keeps the spawning tank stable without a heater.
Growing Out and Colouration
Juvenile kubotai rasboras begin showing their characteristic green fluorescence at around 6-8 weeks. By 12 weeks, they are large enough to join a community tank, though keeping them in a grow-out tank until 1.5 cm reduces losses from competition with adults. A home-bred kubotai that has never been stressed by shipping or shop holding tanks often displays stronger colour than imported specimens. For hobbyists in Singapore interested in micro-fish breeding, this species is an excellent next project after mastering livebearers — something the team at Gensou Aquascaping thoroughly enjoys helping with.
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Still Have Questions About Your Tank?
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5 Everton Park #01-34B, Singapore 080005 · Open daily 11am – 8pm
