Blue Neon Rasbora
Sundadanio axelrodi
Sundadanionidae
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About
The blue neon rasbora is a 2 cm cyprinid from the blackwater streams and peat swamp forests of Borneo, Sumatra and the small islands between them, and it is one of the very few nano fish that genuinely cannot be kept in ordinary tap water. Seriously Fish is unambiguous: it "requires strictly acidic conditions within the range 4.0 – 6.5" and a hardness of 0-5 °H. The other thing worth knowing before you buy is that the name on the tank covers more than one fish. Seriously Fish records that the species "exists in several colour forms depending on locality" - green/blue in the south and east of Sarawak, red/orange in the west - and that in the trade "normally they are just labelled with the distinguishing colour eg. 'red', 'green' or 'blue'". Since 2011 that is a taxonomic problem as well as a labelling one: Conway, Kottelat and Tan's review split the genus into eight species, and Wikipedia now treats true S. axelrodi as endemic to Bintan Island in the Riau Archipelago, while the trade's fish come from Borneo and Sumatra. Reading those two sources together, most of what arrives under this name is one of the seven newer species - that inference is ours, not a quotation. Wild-caught, often in poor condition on import, and unforgiving of chemistry that moves, it is a fish for a mature blackwater tank and a keeper who already runs one.
Care
Soft, acidic blackwater and nothing else: pH 4.0-6.5, 0-5 °dGH, 23-26 °C, dim light, leaf litter and peat, and a mature tank whose chemistry does not swing. Seriously Fish asks for a group of at least 20-30 specimens and warns against adding it to a biologically immature tank; a handful of fish hide, fade and disappear one by one. Expect newly imported fish to arrive in poor condition and to refuse dried food at first - start on live Artemia nauplii, Daphnia and grindal worm, and offer dry and frozen food only once the group is settled, when some fish do learn to take it. Too small and too timid for a general community: house it with Boraras, Trigonostigma or on its own.
Diet
Micropredator. Small live and frozen foods - Artemia nauplii, Daphnia, grindal and micro worm, chopped bloodworm. Dried food is often refused at first, though settled fish may learn to take it over time.
Tankmate compatibility
Gets along with (67)
Possible with care (258)
Avoid (93)
Computed by the AquaSage engine for a spacious reference tank — always check the full verdict for your exact setup in the calculator.
Telling males from females
What works for this species, most reliable first.
- Belly depthA hint only · only on well-fed adults, and only as a comparison
For most tetras, barbs and rasboras this is all there is: a conditioned female is deeper through the belly than a male of the same length.
Also in these lists
Similar species
Same category and the closest water parameters — if this species isn't quite it, start here.
Sold in Lithuania
These Lithuanian shops listed this species in their public catalogue (checked August 8, 2026). Stock moves — ask before you travel.
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Frequently asked questions
- What tank size does a Blue Neon Rasbora need?
- A Blue Neon Rasbora needs an aquarium of at least 45 litres (11.9 US gallons) with a footprint at least 45 cm (17.7 in) long — for this species, swimming length matters as much as raw volume.
- What water parameters does a Blue Neon Rasbora need?
- Blue Neon Rasbora does best at 23–26 °C (73.4–78.8 °F), pH 4–6.5 and a general hardness of 0–5 °dGH.
- What group size does a Blue Neon Rasbora need?
- Blue Neon Rasbora is a social species — keep a group of at least 20 so natural behaviour emerges and stress stays low.
- Is the Blue Neon Rasbora suitable for beginners?
- Blue Neon Rasbora is a demanding species best attempted with some experience — it needs stable, closely watched conditions to thrive.