Neon Blue Rasbora (Sundadanio axelrodi)
A jewel-bright micro-fish from Borneo's blackwater swamps — electric-blue in the right light and perfect for a nano planted tank.
Will it live with a Neon Blue Rasbora?
We compare each fish against your neon blue rasbora on temperament, size, water parameters and swimming zone. Set your tank size and filter the results.
- Blackwing Hatchetfish✅ CompatiblePeaceful · 3.5 cm · Medium care · 23–28 °C (73–82 °F)
- Compatible on the things that matter: shared water near 23–26 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Blackwing Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Celestial Pearl Danio✅ CompatiblePeaceful · 2 cm · Medium care · 22–26 °C (72–79 °F)
- Both are peaceful, and their water overlaps around 23–26 °C — no size, zone or temperament conflicts.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Celestial Pearl Danio in a shoal of 6+ or it gets stressed and nippy.
- Cherry Shrimp✅ CompatiblePeaceful · 3 cm · Easy care · 18–28 °C (64–82 °F)
- Compatible on the things that matter: shared water near 23–26 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Cherry Shrimp in a shoal of 10+ or it gets stressed and nippy.
- Chili Rasbora✅ CompatiblePeaceful · 2 cm · Medium care · 22–28 °C (72–82 °F)
- Compatible on the things that matter: shared water near 23–26 °C, workable temperaments, and no predator-and-prey size gap.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Chili Rasbora in a shoal of 8+ or it gets stressed and nippy.
- Clown Killifish✅ CompatiblePeaceful · 3.5 cm · Medium care · 22–26 °C (72–79 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Clown Killifish in a shoal of 6+ or it gets stressed and nippy.
- Crimson Red Betta✅ CompatiblePeaceful · 3.5 cm · Hard care · 24–29 °C (75–84 °F)
- Both are peaceful, and their water overlaps around 24–26 °C — no size, zone or temperament conflicts.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Crystal Red Shrimp✅ CompatiblePeaceful · 2.5 cm · Hard care · 20–24 °C (68–75 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Crystal Red Shrimp in a shoal of 10+ or it gets stressed and nippy.
- Dawn Tetra✅ CompatiblePeaceful · 2.5 cm · Easy care · 22–28 °C (72–82 °F)
- Compatible on the things that matter: shared water near 23–26 °C, workable temperaments, and no predator-and-prey size gap.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Dawn Tetra in a shoal of 8+ or it gets stressed and nippy.
- Dwarf Spotted Rasbora✅ CompatiblePeaceful · 2.5 cm · Medium care · 23–28 °C (73–82 °F)
- Both are peaceful, and their water overlaps around 23–26 °C — no size, zone or temperament conflicts.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Dwarf Spotted Rasbora in a shoal of 8+ or it gets stressed and nippy.
- Ember Tetra✅ CompatiblePeaceful · 2 cm · Easy care · 24–28 °C (75–82 °F)
- Compatible on the things that matter: shared water near 24–26 °C, workable temperaments, and no predator-and-prey size gap.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Ember Tetra in a shoal of 8+ or it gets stressed and nippy.
- Exclamation Point Rasbora✅ CompatiblePeaceful · 2 cm · Medium care · 22–28 °C (72–82 °F)
- Both are peaceful, and their water overlaps around 23–26 °C — no size, zone or temperament conflicts.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Exclamation Point Rasbora in a shoal of 8+ or it gets stressed and nippy.
- Glowlight Danio✅ CompatiblePeaceful · 3 cm · Easy care · 22–26 °C (72–79 °F)
- Both are peaceful, and their water overlaps around 23–26 °C — no size, zone or temperament conflicts.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Glowlight Danio in a shoal of 8+ or it gets stressed and nippy.
- Gold Ring Danio✅ CompatiblePeaceful · 3 cm · Easy care · 18–26 °C (64–79 °F)
- Both are peaceful, and their water overlaps around 23–26 °C — no size, zone or temperament conflicts.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Gold Ring Danio in a shoal of 8+ or it gets stressed and nippy.
- Green Neon Tetra✅ CompatiblePeaceful · 2.5 cm · Hard care · 24–28 °C (75–82 °F)
- Both are peaceful, and their water overlaps around 24–26 °C — no size, zone or temperament conflicts.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Green Neon Tetra in a shoal of 8+ or it gets stressed and nippy.
- Hummingbird Tetra✅ CompatiblePeaceful · 1.8 cm · Hard care · 22–27 °C (72–81 °F)
- Compatible on the things that matter: shared water near 23–26 °C, workable temperaments, and no predator-and-prey size gap.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Hummingbird Tetra in a shoal of 8+ or it gets stressed and nippy.
- Lambchop Rasbora✅ CompatiblePeaceful · 3 cm · Medium care · 23–28 °C (73–82 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Lambchop Rasbora in a shoal of 6+ or it gets stressed and nippy.
- Neon Green Rasbora✅ CompatiblePeaceful · 2 cm · Easy care · 22–26 °C (72–79 °F)
- Both are peaceful, and their water overlaps around 23–26 °C — no size, zone or temperament conflicts.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Neon Green Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Neon Tetra✅ CompatiblePeaceful · 3 cm · Easy care · 20–26 °C (68–79 °F)
- Both are peaceful, and their water overlaps around 23–26 °C — no size, zone or temperament conflicts.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Neon Tetra in a shoal of 6+ or it gets stressed and nippy.
- Pygmy Corydoras✅ CompatiblePeaceful · 3.2 cm · Easy care · 22–26 °C (72–79 °F)
- Both are peaceful, and their water overlaps around 23–26 °C — no size, zone or temperament conflicts.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Pygmy Corydoras in a shoal of 8+ or it gets stressed and nippy.
- Ruby Tetra✅ CompatiblePeaceful · 2 cm · Medium care · 23–28 °C (73–82 °F)
- Compatible on the things that matter: shared water near 23–26 °C, workable temperaments, and no predator-and-prey size gap.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Ruby Tetra in a shoal of 8+ or it gets stressed and nippy.
- Scarlet Badis✅ CompatibleSemi-aggressive · 2 cm · Medium care · 22–27 °C (72–81 °F)
- Compatible on the things that matter: shared water near 23–26 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Strawberry Rasbora✅ CompatiblePeaceful · 2 cm · Medium care · 23–28 °C (73–82 °F)
- Compatible on the things that matter: shared water near 23–26 °C, workable temperaments, and no predator-and-prey size gap.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Strawberry Rasbora in a shoal of 8+ or it gets stressed and nippy.
- Tail-spot Corydoras✅ CompatiblePeaceful · 3 cm · Easy care · 22–28 °C (72–82 °F)
- Compatible on the things that matter: shared water near 23–26 °C, workable temperaments, and no predator-and-prey size gap.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Tail-spot Corydoras in a shoal of 8+ or it gets stressed and nippy.
- Tiger Shrimp✅ CompatiblePeaceful · 3 cm · Hard care · 20–25 °C (68–77 °F)
- Both are peaceful; temperature, pH and hardness ranges all overlap and neither outsizes the other enough to be a threat.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Tiger Shrimp in a shoal of 6+ or it gets stressed and nippy.
- African Dwarf Frog⚠️ With cautionPeaceful · 4 cm · Medium care · 22–26 °C (72–79 °F)
- Different pH ranges (4–6.5 vs 6.8–7.8); doable if you sit in the shared band, but not ideal long-term.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Assassin Snail⚠️ With cautionPeaceful · 3 cm · Easy care · 22–26 °C (72–79 °F)
- One likes softer water and the other harder (1–6 vs 8–20 dGH) — a compromise, not a perfect match.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Black Darter Tetra⚠️ With cautionSemi-aggressive · 4 cm · Hard care · 21–28 °C (70–82 °F)
- Black Darter Tetra clearly outsizes Neon Blue Rasbora and is semi-aggressive; risky unless the tank is big and well-planted.
- Watch for Black Darter Tetra picking off any neon blue rasbora small enough to fit in its mouth.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Emerald Dwarf Danio⚠️ With cautionPeaceful · 2 cm · Medium care · 20–24 °C (68–75 °F)
- pH preferences only just meet (Neon Blue Rasbora 4–6.5 vs Emerald Dwarf Danio 7–8) — target the overlap and acclimate slowly.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Emerald Dwarf Danio in a shoal of 8+ or it gets stressed and nippy.
- Endler's Livebearer⚠️ With cautionPeaceful · 3 cm · Easy care · 22–28 °C (72–82 °F)
- pH preferences only just meet (Neon Blue Rasbora 4–6.5 vs Endler's Livebearer 7–8.5) — target the overlap and acclimate slowly.
- One likes softer water and the other harder (1–6 vs 10–25 dGH) — a compromise, not a perfect match.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Endler's Livebearer in a shoal of 6+ or it gets stressed and nippy.
- Malaysian Trumpet Snail⚠️ With cautionPeaceful · 3 cm · Easy care · 21–27 °C (70–81 °F)
- pH preferences only just meet (Neon Blue Rasbora 4–6.5 vs Malaysian Trumpet Snail 7–8) — target the overlap and acclimate slowly.
- One likes softer water and the other harder (1–6 vs 8–18 dGH) — a compromise, not a perfect match.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Nerite Snail⚠️ With cautionPeaceful · 2.5 cm · Easy care · 22–28 °C (72–82 °F)
- pH preferences only just meet (Neon Blue Rasbora 4–6.5 vs Nerite Snail 7–8.5) — target the overlap and acclimate slowly.
- One likes softer water and the other harder (1–6 vs 8–18 dGH) — a compromise, not a perfect match.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Pea Puffer⚠️ With cautionSemi-aggressive · 2.5 cm · Medium care · 24–28 °C (75–82 °F)
- Pea Puffer and Neon Blue Rasbora are close in size, but the semi-aggressive one tends to dominate — add neon blue rasbora in a group to spread the pressure.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Rainbow Emperor Tetra⚠️ With cautionSemi-aggressive · 3.6 cm · Medium care · 22–28 °C (72–82 °F)
- Rainbow Emperor Tetra is semi-aggressive and may chase or nip the smaller Neon Blue Rasbora — plant heavily and break up sight lines.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
- Ramshorn Snail⚠️ With cautionPeaceful · 2 cm · Easy care · 20–28 °C (68–82 °F)
- Different pH ranges (4–6.5 vs 7–8); doable if you sit in the shared band, but not ideal long-term.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Red Lip Nerite Snail⚠️ With cautionPeaceful · 2 cm · Easy care · 22–28 °C (72–82 °F)
- pH preferences only just meet (Neon Blue Rasbora 4–6.5 vs Red Lip Nerite Snail 7–8) — target the overlap and acclimate slowly.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Rummy Nose Rasbora⚠️ With cautionPeaceful · 4 cm · Medium care · 20–26 °C (68–79 °F)
- pH preferences only just meet (Neon Blue Rasbora 4–6.5 vs Rummy Nose Rasbora 7–8) — target the overlap and acclimate slowly.
- One likes softer water and the other harder (1–6 vs 8–16 dGH) — a compromise, not a perfect match.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Rummy Nose Rasbora in a shoal of 8+ or it gets stressed and nippy.
- Serpae Tetra⚠️ With cautionSemi-aggressive · 4 cm · Easy care · 23–28 °C (73–82 °F)
- Serpae Tetra clearly outsizes Neon Blue Rasbora and is semi-aggressive; risky unless the tank is big and well-planted.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Keep Serpae Tetra in a shoal of 6+ or it gets stressed and nippy.
- Tiger Badis⚠️ With cautionSemi-aggressive · 4 cm · Medium care · 22–24 °C (72–75 °F)
- Expect Tiger Badis to harass Neon Blue Rasbora at times; give dense cover and watch them at feeding.
- Tiger Badis may hunt Neon Blue Rasbora, fry or shrimplets — safest in a heavily planted tank.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Trinidad Guppy⚠️ With cautionPeaceful · 3 cm · Easy care · 19–24 °C (66–75 °F)
- pH preferences only just meet (Neon Blue Rasbora 4–6.5 vs Trinidad Guppy 6.6–7.5) — target the overlap and acclimate slowly.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Wine Red Betta⚠️ With cautionAggressive · 5 cm · Medium care · 24–28 °C (75–82 °F)
- Wine Red Betta clearly outsizes Neon Blue Rasbora and is aggressive; risky unless the tank is big and well-planted.
- Watch for Wine Red Betta picking off any neon blue rasbora small enough to fit in its mouth.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Alligator Gar⛔ Not recommendedAggressive · 250 cm · Hard care · 24–28 °C (75–82 °F)
- Size gap is too large (250 vs 2.5 cm): Alligator Gar will treat Neon Blue Rasbora as food.
- Different pH ranges (4–6.5 vs 6.8–7.8); doable if you sit in the shared band, but not ideal long-term.
- Expect Alligator Gar to harass Neon Blue Rasbora at times; give dense cover and watch them at feeding.
- Your 75 L tank is below the ~3785 L this pairing really wants — crowding raises aggression.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Clown Knifefish⛔ Not recommendedAggressive · 90 cm · Hard care · 24–28 °C (75–82 °F)
- Clown Knifefish (90 cm) is big enough to swallow the 2.5 cm Neon Blue Rasbora whole.
- Clown Knifefish is aggressive and may chase or nip the smaller Neon Blue Rasbora — plant heavily and break up sight lines.
- Your 75 L tank is below the ~750 L this pairing really wants — crowding raises aggression.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Fire Eel⛔ Not recommendedSemi-aggressive · 100 cm · Medium care · 24–28 °C (75–82 °F)
- Fire Eel (100 cm) is big enough to swallow the 2.5 cm Neon Blue Rasbora whole.
- Expect Fire Eel to harass Neon Blue Rasbora at times; give dense cover and watch them at feeding.
- Your 75 L tank is below the ~380 L this pairing really wants — crowding raises aggression.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Koi⛔ Not recommendedPeaceful · 90 cm · Medium care · 4–28 °C (39–82 °F)
- Koi (90 cm) is big enough to swallow the 2.5 cm Neon Blue Rasbora whole.
- One likes softer water and the other harder (1–6 vs 9–18 dGH) — a compromise, not a perfect match.
- Your 75 L tank is below the ~3800 L this pairing really wants — crowding raises aggression.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Redtail Catfish⛔ Not recommendedAggressive · 120 cm · Hard care · 24–27 °C (75–81 °F)
- Neon Blue Rasbora is bite-sized to a 120 cm predatory redtail catfish — it will be eaten.
- Expect Redtail Catfish to harass Neon Blue Rasbora at times; give dense cover and watch them at feeding.
- Your 75 L tank is below the ~5700 L this pairing really wants — crowding raises aggression.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Spotted Gar⛔ Not recommendedAggressive · 90 cm · Hard care · 18–26 °C (64–79 °F)
- Neon Blue Rasbora is bite-sized to a 90 cm predatory spotted gar — it will be eaten.
- Expect Spotted Gar to harass Neon Blue Rasbora at times; give dense cover and watch them at feeding.
- Your 75 L tank is below the ~600 L this pairing really wants — crowding raises aggression.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Wels Catfish⛔ Not recommendedAggressive · 300 cm · Hard care · 15–25 °C (59–77 °F)
- Wels Catfish (300 cm) is big enough to swallow the 2.5 cm Neon Blue Rasbora whole.
- Expect Wels Catfish to harass Neon Blue Rasbora at times; give dense cover and watch them at feeding.
- Your 75 L tank is below the ~20000 L this pairing really wants — crowding raises aggression.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
- Wolf Cichlid⛔ Not recommendedAggressive · 72 cm · Hard care · 24–30 °C (75–86 °F)
- Neon Blue Rasbora is bite-sized to a 72 cm predatory wolf cichlid — it will be eaten.
- pH preferences only just meet (Neon Blue Rasbora 4–6.5 vs Wolf Cichlid 7–8) — target the overlap and acclimate slowly.
- One likes softer water and the other harder (1–6 vs 8–20 dGH) — a compromise, not a perfect match.
- Wolf Cichlid clearly outsizes Neon Blue Rasbora and is aggressive; risky unless the tank is big and well-planted.
- Your 75 L tank is below the ~760 L this pairing really wants — crowding raises aggression.
- Keep Neon Blue Rasbora in a shoal of 10+ or it gets stressed and nippy.
Compatibility is computed from each species' care data — a strong starting point, not a guarantee. Individual temperament varies, so always introduce new fish slowly and watch them.
Neon Blue Rasbora care specs
- Care level
- Medium
- Breeding
- Hard
- Max size
- 2.5 cm (1 in)
- Min tank size
- 40 L (10.6 gal)
- Temperature
- 23–26 °C (73–79 °F)
- pH
- 4–6.5
- Hardness
- 1–6 dGH
- Lifespan
- 3–5 years
- Diet
- Omnivore
- Swim level
- Middle
- Group size
- 10+ (shoaling)
- Family
- Cyprinidae
- Origin
- Southeast Asia — blackwater peat swamps of Borneo and Sumatra
What is a Neon Blue Rasbora?
The Neon Blue Rasbora (Sundadanio axelrodi) is a micro-sized cyprinid from the dark, tannic peat-swamp streams of Borneo and Sumatra. Reaching just 2.5 cm (1 in) at maximum size, it is among the smallest fish kept in the hobby, yet its iridescent electric-blue lateral stripe — which blazes like a neon filament under good aquarium lighting — gives it a visual presence far beyond its dimensions. Despite being sold under names containing “rasbora” or “danio”, it belongs to its own distinct genus (Sundadanio), which is found only on the island of Borneo and neighbouring Sumatra.
Neon Blue Rasboras are rated medium care — not because they are fragile, but because they are uncompromising about soft, acidic blackwater chemistry. Once the water column is correctly set up they are robust, active and long-lived. Allow pH or hardness to drift toward tap-water neutral and they will slowly decline. Nail the chemistry and they are among the most rewarding nano fish available.
Where do Neon Blue Rasboras come from?
Wild Sundadanio axelrodi inhabit heavily shaded, slow-moving blackwater habitats: peat swamps, leaf-littered forest streams and flooded forest floors across Borneo and Sumatra in Southeast Asia. These environments are stained brown-black by decomposing plant matter — principally tannins and humic acids leaching from rotting leaves and peat. The result is water that is extremely soft (1–6 dGH), strongly acidic (pH 4.0–6.5) and very low in dissolved minerals. Light penetration is minimal, temperatures are moderate at 23–26 °C (73–79 °F), and the substrate is typically dark sand or bare earth covered in layers of fallen leaves.
Understanding this origin is the entire key to keeping them well. Every aspect of setup — water chemistry, lighting, decor, tank-mates — should mirror that dim, soft, leafy blackwater world.
What tank size and setup do Neon Blue Rasboras need?
A group of ten — the minimum school size — can be housed in 40 litres (10.5 gal), making this a genuine nano-tank species. Larger tanks in the 60–80 L (16–21 gal) range are more forgiving and show off a full shoal beautifully.
Key setup points:
- Substrate: Dark fine sand or smooth small gravel. Dark colours settle the fish and intensify the blue stripe.
- Leaves and botanicals: A generous litter of dried Indian almond (Terminalia catappa) leaves, alder cones or dried oak leaves is essential. They acidify the water, soften light and provide the microhabitat the fish expect.
- Filtration: A slow sponge filter or small hang-on filter set to low flow. These fish come from near-stagnant water; strong current stresses them and disrupts shoaling.
- Planting: Dense planting with Java fern, Bucephalandra, mosses and floating plants such as frogbit creates the dim, broken-light environment they thrive in.
- Lid: Mandatory. Despite their small size, Neon Blue Rasboras can and do jump through gaps.
- Lighting: Dim to moderate. Floating plants or a dimmable fixture prevents harsh top-down light and keeps the fish comfortable.
What water parameters do Neon Blue Rasboras need?
| Parameter | Target range |
|---|---|
| Temperature | 23–26 °C (73–79 °F) |
| pH | 4.0–6.5 |
| Hardness | 1–6 dGH |
These are non-negotiable parameters. Standard municipal tap water in most regions is far too hard and too neutral — even “soft” tap water commonly reads 6–10 dGH and pH 7+, which will stress these fish chronically. The correct approach is to use RO (reverse osmosis) water or collected rainwater, remineralised lightly to achieve 1–4 dGH, then acidified to the target pH range using peat filtration, Indian almond leaf extract or a commercial blackwater conditioner.
Consistency matters as much as the numbers. Install a reliable digital pH pen and a dGH test kit and check monthly once the system is stable. Large water changes with untreated tap water can cause rapid parameter swings — use matched RO water for all top-ups and water changes.
What do Neon Blue Rasboras eat?
Neon Blue Rasboras are omnivores with a strong preference for tiny live and frozen prey in the wild. In the aquarium they will accept a variety of foods, but their tiny mouth size — around 1 mm gape — means standard tropical flake is too large for comfortable feeding.
Ideal foods:
- Micro-pellets formulated for nano fish (0.3–0.5 mm diameter)
- Micro-powder foods such as Hikari First Bites or Sera Micron
- Baby brine shrimp (newly hatched nauplii — a superb conditioning food)
- Micro-worms and vinegar eels
- Daphnia — particularly the small Moina species
- Frozen cyclops or small bloodworm pieces
Feed small portions twice daily, only what is consumed in two to three minutes. Uneaten food decays rapidly in a soft-acidic tank and disrupts the chemistry. Variety across the week keeps the fish well-conditioned and colourful.
What is the behaviour of Neon Blue Rasboras, and what fish can live with them?
Sundadanio axelrodi are peaceful, mid-water shoalers that spend most of their time cruising as a loose group through the middle layers of the tank. A school of 10 or more moves with a cohesion and flash of blue that makes even a modest planted nano tank look spectacular. Below 10 individuals they become shy and stressed; 15–20 is a better target if the tank allows.
Because they reach only 2.5 cm (1 in), tank-mate selection is critical. Any fish large enough to fit a Neon Blue Rasbora in its mouth is a predator, regardless of its listed temperament. Restrict companions to species of similar size and matching soft-acidic water requirements.
Good tank-mate choices include chili rasboras (Boraras brigittae), ember tetras (Hyphessobrycon amandae), exclamation point rasboras, pygmy Corydoras (Corydoras pygmaeus or C. hastatus), dwarf otocinclus, and nano shrimp such as Neocaridina or Caridina species kept in appropriately acidic water. Peaceful snails (ramshorn, nerite) are also compatible.
Avoid cichlids, barbs known to nip, and any fish exceeding 4–5 cm — even ostensibly peaceful ones can intimidate or accidentally consume fish this small.
For a full compatible-species list with filter options, see Neon Blue Rasbora tank mates.
How do you tell male from female Neon Blue Rasboras?
Sexual dimorphism is subtle but visible to a trained eye, especially in a well-conditioned group. Males develop a brighter, more intensely saturated electric-blue lateral stripe and are marginally slimmer in the body. Colouration intensifies noticeably during spawning condition. Females are slightly rounder and deeper in the abdomen — particularly obvious when carrying eggs — and their lateral stripe, while still present and iridescent, is marginally less vivid than a dominant male’s.
Sexing juveniles below 1.5 cm is unreliable. Buy a group of at least 10 unsexed individuals and both sexes will almost certainly be represented.
How do Neon Blue Rasboras breed?
Breeding is rated hard — achievable by experienced nano-fish keepers who can meet the requirements, but not a casual project. The main challenges are replicating the extreme blackwater conditions that trigger spawning and successfully raising the near-microscopic fry.
A dedicated breeding setup of 10–20 L (2.5–5 gal) should contain very soft RO water at pH 4.5–5.5, temperature raised slightly to 25–26 °C (77–79 °F), fine-leaved plants or Java moss for egg deposition, and a gentle air-driven sponge filter. Condition a group of adults on live baby brine shrimp and micro-worms for two to three weeks before introducing a pair or small group to the breeding tank.
Spawning is a scatter-and-ignore affair: eggs are deposited among plants and the parents show no parental care, so remove adults after spawning. Eggs hatch in roughly 24–48 hours; fry are extremely small and require infusoria or commercial liquid fry food for the first week before graduating to baby brine shrimp nauplii. Maintaining pH stability during the fry stage is critical — any drift toward neutral is often fatal at this size.
What diseases affect Neon Blue Rasboras?
Species kept in correct blackwater conditions are genuinely hardy and disease incidence is low. The diseases that do appear are almost always secondary to water-quality failures.
- Ich (Ichthyophthirius multifiliis): White pinhead spots across body and fins. Classic result of temperature fluctuation or chilling below 23 °C. Gradual temperature increase (within the safe range) and improved water quality address early cases. Quarantine new additions to prevent introduction.
- Velvet (Oodinium): Fine gold or rust-coloured dusty coating, often noticed first on the flanks under raking light. Highly contagious; isolate affected fish promptly. Driven by stress and poor water quality.
- Bacterial fin rot: Fraying or whitening fin edges, usually in fish subjected to elevated pH or sudden parameter changes. Correct the water chemistry first; fin regrowth follows once conditions stabilise.
- Wasting / failure to thrive: A vague decline — fish become pallid, stop schooling and lose weight over weeks. Usually indicates chronically incorrect pH or hardness rather than an infectious pathogen. Test the water before assuming disease.
Prevention rests on three pillars: correct blackwater chemistry maintained consistently, a thorough four-week quarantine for all new fish and plants, and avoiding overfeeding that degrades the water column.
Health note: Disease diagnosis and medication dosing are outside the scope of a care profile. Before treating a sick fish, cross-reference symptoms with a reputable fish-health or veterinary source, and always confirm water parameters are correct first — most treatments are ineffective if the underlying water quality issue remains.
How long do Neon Blue Rasboras live?
A well-maintained Neon Blue Rasbora lives 3–5 years. This is a reasonable lifespan for a fish of this size, and the upper end is achievable with correct blackwater chemistry, varied nutrition and a stable, stress-free environment. Fish kept in suboptimal pH or hardness — even if technically alive — rarely reach their potential lifespan and typically show faded colouration and suppressed immune function long before they die.
Buy from a reputable supplier who stocks them in soft-water conditions, and transition them to your setup slowly. A group that arrives healthy and settles into correctly prepared blackwater will reward you with years of striking, iridescent colour in the middle of your tank.
Frequently asked questions
What water parameters does the Neon Blue Rasbora need?
They require genuinely soft, acidic blackwater conditions: pH 4.0–6.5 and hardness 1–6 dGH. Neutral or hard tap water will stress them over time. RO water buffered with Indian almond leaves or peat is the most reliable approach.
Can Neon Blue Rasboras live with other fish?
Yes, but only with similarly tiny, soft-water species. Good tank-mates include ember tetras, chili rasboras, small Corydoras, and nano shrimp. Avoid any fish large enough to eat them — at 2.5 cm they are vulnerable to anything mid-sized or larger.
What you need to keep a neon blue rasbora
The baseline is a heated, filtered 40 L+ tank: a reliable heater to hold 23–26 °C (73–79 °F), a gentle filter that won't batter a neon blue rasbora in the current, and a tight-fitting lid. Cycle the tank fully before adding any fish.
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