Blue axelrodi rasbora
Sundadanio axelrodi
intermediate careOverview
The blue axelrodi rasbora (Sundadanio axelrodi) is a true blackwater jewel — a shoaling nano barely 2 cm long that shimmers iridescent blue-green with a fiery red or orange fin flush. It comes from soft, acidic, tannin-stained peat streams on Borneo and neighbouring islands, and it is one of the most beautiful of all the tiny “micro” fish. It is also a specialist that needs soft water and a mature, stable tank to show its best.
Tank & water
A large shoal thrives in a mature, planted 30-litre (8-gallon) blackwater tank or larger.
- Water: soft and acidic, pH 4.5–6.5, is the key; stain the water with tannins from leaf litter and botanicals. Hard tap water is a poor match — see how do I soften aquarium water.
- Temperature: 23–27 °C from a small heater.
- Gentle flow, dim light: a soft sponge filter and shady planting suit these shy fish.
- Mature and stable: add them only to a long-cycled, settled tank.
Feeding
These are tiny micropredators with minute mouths. Offer fine powdered and crushed micro-foods, supplemented generously with small live and frozen fare — baby brine shrimp, cyclops, microworm and daphnia. Many foods are simply too large; size everything down and feed little and often so it reaches these small, shy fish.
Behaviour & tankmates
Keep a big, peaceful shoal in a species tank or alongside other calm soft-water nanos such as chili rasboras, celestial pearl danios and dwarf shrimp. Avoid anything fast, large or nippy that will intimidate them or eat their food. Dense planting and dim light bring out their confidence and colour.
Acclimatise new fish slowly, as they cope poorly with a sudden move from soft shop water into different parameters, and give them a week or two of quiet to settle before expecting full colour. Frequent small water changes with matched soft water keep the tank stable without shocking them.
Give the blue axelrodi rasbora a mature, soft-water blackwater nano and a full shoal, and few fish pack so much iridescent colour into so little space — see our best nano aquarium picks.
Blue axelrodi rasbora — frequently asked questions
Is Sundadanio axelrodi hard to keep?
It is a sensitive nano that needs soft, acidic, mature blackwater and dislikes hard tap water and a fresh, unstable tank. Once settled in the right conditions it is not fragile, but its need for soft water and tiny live foods, plus its shyness, put it above a beginner community fish.
What colour is the blue axelrodi rasbora?
Despite the name, the species comes in several colour forms, from an iridescent green-blue body to a more red-toned variety, all with a bright red or orange fin flush in males. In a mature soft-water shoal and good light the colours are spectacular for such a tiny fish.
How many should I keep?
Keep a large shoal of at least ten to twelve. These fish are naturally social and nervous; in a big group they display, colour up and use the open water, while a small group hides and stays pale. Their tiny size means even a modest nano can hold a good shoal.
Found your model? Buy it at the right price.
UniverTrack tracks the real price of your aquarium gear across several retailers, spots fake discounts and warns you when it's genuinely the right moment to buy — with an AI assistant to guide you.