Photo: Lerdsuwa (CC BY-SA 3.0) — via Wikimedia Commons
Blue Danio (Danio kerri)
A powder-blue, fast-moving schooler from southern Thailand that thrives in almost any peaceful community tank.
Will it live with a Blue Danio?
We compare each fish against your blue danio on temperament, size, water parameters and swimming zone. Set your tank size and filter the results.
- African Dwarf Frog✅ CompatiblePeaceful · 4 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 Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Amapá Tetra✅ CompatiblePeaceful · 4 cm · Medium care · 24–27 °C (75–81 °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 Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Amapá Tetra in a shoal of 6+ or it gets stressed and nippy.
- Black Phantom Tetra✅ CompatiblePeaceful · 4.5 cm · Easy care · 22–28 °C (72–82 °F)
- Both are peaceful, and their water overlaps around 22–26 °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 Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Black Phantom Tetra in a shoal of 6+ or it gets stressed and nippy.
- Blue Emperor Tetra✅ CompatiblePeaceful · 4 cm · Medium care · 23–27 °C (73–81 °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 Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Blue Emperor Tetra in a shoal of 6+ or it gets stressed and nippy.
- Cardinal Tetra✅ CompatiblePeaceful · 4 cm · Medium care · 23–27 °C (73–81 °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 Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Cardinal Tetra in a shoal of 6+ or it gets stressed and nippy.
- Emperor Tetra✅ CompatiblePeaceful · 4 cm · Easy care · 23–27 °C (73–81 °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 Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Emperor Tetra in a shoal of 6+ or it gets stressed and nippy.
- Flame Tetra✅ CompatiblePeaceful · 4 cm · Easy care · 22–28 °C (72–82 °F)
- Compatible on the things that matter: shared water near 22–26 °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 Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Flame Tetra in a shoal of 6+ or it gets stressed and nippy.
- Glowlight Tetra✅ CompatiblePeaceful · 4 cm · Easy care · 22–28 °C (72–82 °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 Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Glowlight Tetra in a shoal of 6+ or it gets stressed and nippy.
- Gold Tetra✅ CompatiblePeaceful · 4.5 cm · Easy 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 Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Gold Tetra in a shoal of 6+ or it gets stressed and nippy.
- Golden Dwarf Barb✅ CompatiblePeaceful · 4 cm · Easy care · 18–24 °C (64–75 °F)
- Both are peaceful, and their water overlaps around 21–24 °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 Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Golden Dwarf Barb in a shoal of 6+ or it gets stressed and nippy.
- Jelly Bean Tetra✅ CompatiblePeaceful · 4 cm · Medium care · 20–26 °C (68–79 °F)
- Both are peaceful, and their water overlaps around 21–26 °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 Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Jelly Bean Tetra in a shoal of 10+ or it gets stressed and nippy.
- Marbled Hatchetfish✅ CompatiblePeaceful · 4 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.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Marbled Hatchetfish in a shoal of 6+ or it gets stressed and nippy.
- Otocinclus✅ CompatiblePeaceful · 4 cm · Medium care · 21–26 °C (70–79 °F)
- Both are peaceful, and their water overlaps around 21–26 °C — no size, zone or temperament conflicts.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Otocinclus in a shoal of 6+ or it gets stressed and nippy.
- Phoenix Tetra✅ CompatiblePeaceful · 4 cm · Easy 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 Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Phoenix Tetra in a shoal of 8+ or it gets stressed and nippy.
- Purple Tetra✅ CompatiblePeaceful · 4 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.
- Both favour the middle of the tank — offer enough cover so they aren't always in each other's space.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Purple Tetra in a shoal of 8+ or it gets stressed and nippy.
- Rainbow Emperor Tetra✅ CompatibleSemi-aggressive · 3.6 cm · Medium care · 22–28 °C (72–82 °F)
- Compatible on the things that matter: shared water near 22–26 °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 Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Rainbow Emperor Tetra in a shoal of 8+ or it gets stressed and nippy.
- Red Phantom Tetra✅ CompatiblePeaceful · 4 cm · Easy care · 22–28 °C (72–82 °F)
- Both are peaceful, and their water overlaps around 22–26 °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 Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Red Phantom Tetra in a shoal of 8+ or it gets stressed and nippy.
- Rosy Tetra✅ CompatiblePeaceful · 4 cm · Easy care · 22–28 °C (72–82 °F)
- Both are peaceful, and their water overlaps around 22–26 °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 Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Rosy Tetra in a shoal of 6+ or it gets stressed and nippy.
- Rummy Nose Rasbora✅ CompatiblePeaceful · 4 cm · Medium care · 20–26 °C (68–79 °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 Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Rummy Nose Rasbora in a shoal of 8+ or it gets stressed and nippy.
- Sparkling Gourami✅ CompatiblePeaceful · 4 cm · Medium care · 24–28 °C (75–82 °F)
- Both are peaceful, and their water overlaps around 24–26 °C — no size, zone or temperament conflicts.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Strawberry Betta✅ CompatiblePeaceful · 4 cm · Medium care · 22–27 °C (72–81 °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 Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Threadfin Rainbowfish✅ CompatiblePeaceful · 4 cm · Medium care · 24–28 °C (75–82 °F)
- Both are peaceful, and their water overlaps around 24–26 °C — no size, zone or temperament conflicts.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Threadfin Rainbowfish in a shoal of 6+ or it gets stressed and nippy.
- Tiger Otocinclus✅ CompatiblePeaceful · 4 cm · Medium care · 22–27 °C (72–81 °F)
- Compatible on the things that matter: shared water near 22–26 °C, workable temperaments, and no predator-and-prey size gap.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Tiger Otocinclus in a shoal of 6+ or it gets stressed and nippy.
- Yellow Phantom Tetra✅ CompatiblePeaceful · 4 cm · Easy care · 23–27 °C (73–81 °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 Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Yellow Phantom Tetra in a shoal of 6+ 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 and Blue Danio are close in size, but the semi-aggressive one tends to dominate — add blue danio in a group to spread the pressure.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Black Ruby Barb⚠️ With cautionSemi-aggressive · 6 cm · Easy care · 22–26 °C (72–79 °F)
- Black Ruby Barb and Blue Danio are close in size, but the semi-aggressive one tends to dominate — add blue danio in a group to spread the pressure.
- Your 75 L tank is below the ~100 L this pairing really wants — crowding raises aggression.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Black Ruby Barb in a shoal of 6+ or it gets stressed and nippy.
- Black Skirt Tetra⚠️ With cautionSemi-aggressive · 6 cm · Easy care · 20–26 °C (68–79 °F)
- Black Skirt Tetra is semi-aggressive and may chase or nip the smaller Blue Danio — plant heavily and break up sight lines.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Black Skirt Tetra in a shoal of 6+ or it gets stressed and nippy.
- Cherry Shrimp⚠️ With cautionPeaceful · 3 cm · Easy care · 18–28 °C (64–82 °F)
- Blue Danio may eat Cherry Shrimp or pick off its shrimplets — a densely planted tank with moss gives them a fighting chance.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Cherry Shrimp in a shoal of 10+ or it gets stressed and nippy.
- Chocolate Gourami⚠️ With cautionPeaceful · 5 cm · Hard care · 25–30 °C (77–86 °F)
- pH preferences only just meet (Blue Danio 6.5–7.5 vs Chocolate Gourami 4–6) — target the overlap and acclimate slowly.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Chocolate Gourami in a shoal of 6+ or it gets stressed and nippy.
- Fire Red Licorice Gourami⚠️ With cautionPeaceful · 3.5 cm · Hard care · 23–28 °C (73–82 °F)
- Water hardness preferences differ (Blue Danio 5–15 vs Fire Red Licorice Gourami 0–4 dGH).
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Ghost Shrimp⚠️ With cautionPeaceful · 4 cm · Easy care · 18–28 °C (64–82 °F)
- Blue Danio may eat Ghost Shrimp or pick off its shrimplets — a densely planted tank with moss gives them a fighting chance.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Ghost Shrimp in a shoal of 6+ or it gets stressed and nippy.
- Humpbacked Tetra⚠️ With cautionSemi-aggressive · 5 cm · Hard care · 24–28 °C (75–82 °F)
- Humpbacked Tetra and Blue Danio are close in size, but the semi-aggressive one tends to dominate — add blue danio in a group to spread the pressure.
- Your 75 L tank is below the ~80 L this pairing really wants — crowding raises aggression.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Humpbacked Tetra in a shoal of 8+ or it gets stressed and nippy.
- Morse Code Corydoras⚠️ With cautionPeaceful · 5 cm · Medium care · 23–26 °C (73–79 °F)
- Your 75 L tank is below the ~80 L this pairing really wants — crowding raises aggression.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Morse Code Corydoras in a shoal of 6+ or it gets stressed and nippy.
- Serpae Tetra⚠️ With cautionSemi-aggressive · 4 cm · Easy care · 23–28 °C (73–82 °F)
- Serpae Tetra and Blue Danio are close in size, but the semi-aggressive one tends to dominate — add blue danio in a group to spread the pressure.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Serpae Tetra in a shoal of 6+ or it gets stressed and nippy.
- Silvertip Tetra⚠️ With cautionSemi-aggressive · 5 cm · Easy care · 22–28 °C (72–82 °F)
- Silvertip Tetra is semi-aggressive and may chase or nip the smaller Blue Danio — plant heavily and break up sight lines.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Silvertip Tetra in a shoal of 6+ or it gets stressed and nippy.
- Spotfin Betta⚠️ With cautionSemi-aggressive · 5 cm · Medium care · 23–28 °C (73–82 °F)
- Spotfin Betta is semi-aggressive and may chase or nip the smaller Blue Danio — plant heavily and break up sight lines.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Striped Red-Eye Puffer⚠️ With cautionAggressive · 5 cm · Hard care · 24–28 °C (75–82 °F)
- Striped Red-Eye Puffer and Blue Danio are close in size, but the aggressive one tends to dominate — add blue danio in a group to spread the pressure.
- Keep Blue Danio 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)
- Tiger Badis and Blue Danio are close in size, but the semi-aggressive one tends to dominate — add blue danio in a group to spread the pressure.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Tiger Shrimp⚠️ With cautionPeaceful · 3 cm · Hard care · 20–25 °C (68–77 °F)
- Blue Danio may eat Tiger Shrimp or pick off its shrimplets — a densely planted tank with moss gives them a fighting chance.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Keep Tiger Shrimp in a shoal of 6+ or it gets stressed and nippy.
- Wine Red Betta⚠️ With cautionAggressive · 5 cm · Medium care · 24–28 °C (75–82 °F)
- One likes softer water and the other harder (5–15 vs 0–4 dGH) — a compromise, not a perfect match.
- Expect Wine Red Betta to harass Blue Danio at times; give dense cover and watch them at feeding.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Alligator Gar⛔ Not recommendedAggressive · 250 cm · Hard care · 24–28 °C (75–82 °F)
- Blue Danio is bite-sized to a 250 cm predatory alligator gar — it will be eaten.
- Expect Alligator Gar to harass Blue Danio 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 Blue Danio in a shoal of 6+ 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 4 cm Blue Danio whole.
- Expect Clown Knifefish to harass Blue Danio at times; give dense cover and watch them at feeding.
- Your 75 L tank is below the ~750 L this pairing really wants — crowding raises aggression.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Fire Eel⛔ Not recommendedSemi-aggressive · 100 cm · Medium care · 24–28 °C (75–82 °F)
- Size gap is too large (100 vs 4 cm): Fire Eel will treat Blue Danio as food.
- Expect Fire Eel to harass Blue Danio 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 Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Koi⛔ Not recommendedPeaceful · 90 cm · Medium care · 4–28 °C (39–82 °F)
- Size gap is too large (90 vs 4 cm): Koi will treat Blue Danio as food.
- Your 75 L tank is below the ~3800 L this pairing really wants — crowding raises aggression.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Redtail Catfish⛔ Not recommendedAggressive · 120 cm · Hard care · 24–27 °C (75–81 °F)
- Size gap is too large (120 vs 4 cm): Redtail Catfish will treat Blue Danio as food.
- Redtail Catfish clearly outsizes Blue Danio and is aggressive; risky unless the tank is big and well-planted.
- Your 75 L tank is below the ~5700 L this pairing really wants — crowding raises aggression.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Spotted Gar⛔ Not recommendedAggressive · 90 cm · Hard care · 18–26 °C (64–79 °F)
- Size gap is too large (90 vs 4 cm): Spotted Gar will treat Blue Danio as food.
- Spotted Gar is aggressive and may chase or nip the smaller Blue Danio — plant heavily and break up sight lines.
- Your 75 L tank is below the ~600 L this pairing really wants — crowding raises aggression.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Wels Catfish⛔ Not recommendedAggressive · 300 cm · Hard care · 15–25 °C (59–77 °F)
- Size gap is too large (300 vs 4 cm): Wels Catfish will treat Blue Danio as food.
- Wels Catfish clearly outsizes Blue Danio and is aggressive; risky unless the tank is big and well-planted.
- Your 75 L tank is below the ~20000 L this pairing really wants — crowding raises aggression.
- Keep Blue Danio in a shoal of 6+ or it gets stressed and nippy.
- Wolf Cichlid⛔ Not recommendedAggressive · 72 cm · Hard care · 24–30 °C (75–86 °F)
- Blue Danio is bite-sized to a 72 cm predatory wolf cichlid — it will be eaten.
- Wolf Cichlid is aggressive and may chase or nip the smaller Blue Danio — plant heavily and break up sight lines.
- Your 75 L tank is below the ~760 L this pairing really wants — crowding raises aggression.
- Keep Blue Danio in a shoal of 6+ 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.
Blue Danio care specs
- Care level
- Easy
- Breeding
- Medium
- Max size
- 4 cm (1.6 in)
- Min tank size
- 60 L (15.9 gal)
- Temperature
- 21–26 °C (70–79 °F)
- pH
- 6.5–7.5
- Hardness
- 5–15 dGH
- Lifespan
- 3–5 years
- Diet
- Omnivore
- Swim level
- Middle
- Group size
- 6+ (shoaling)
- Family
- Cyprinidae
- Origin
- Southern Thailand and nearby islands (Phuket, Ko Lanta, Langkawi)
What is a Blue Danio?
The Blue Danio (Danio kerri), also sold as Kerr’s Danio or the Blue-striped Danio, is a small, active schooling fish native to the slow-moving streams, floodplain pools and lowland rivulets of southern Thailand and the surrounding islands — including Phuket, Ko Lanta and Langkawi just across the Malaysian border. First described scientifically in 1929, it has been a staple of the aquarium trade for decades, though it remains slightly less familiar than its close relative the Zebra Danio.
Adults are compact, topping out at around 4 cm (1.6 in). The body is a soft powder blue to blue-green, overlaid with one or two pinkish-yellow lateral stripes that run from the gill cover to the base of the tail. Under good lighting or reflected sunlight the flanks carry a subtle metallic sheen that shifts between blue and gold depending on the angle — exactly the kind of shimmer that makes a fast-moving shoal mesmerising to watch.
What makes the Blue Danio particularly appealing for community aquariums is its combination of genuine beauty, ease of care and completely peaceful temperament. The species adapts to a wide band of water conditions and takes most commercial foods readily. If the tank is cycled and the group is large enough, very little else is required.
Where do Blue Danios come from?
Wild Blue Danios inhabit the lowland freshwater systems of the Thai-Malay Peninsula — specifically, the southern Thai provinces and the islands of Phuket, Ko Lanta and the Malaysian island of Langkawi. These habitats are typically slow-moving or almost still: shallow forest streams, flooded rice paddies, drainage channels and the vegetated margins of larger rivers.
The water in these systems is warm and soft, filtered through sand and leaf litter, with pH tending toward mildly acidic to neutral. This geography explains why the Blue Danio does so well across a broad range of aquarium conditions — it evolved in environments that vary seasonally — and why heavily planted tanks with some open water and a moderate current feel natural to it.
What size tank does a Blue Danio need?
The practical minimum for a group of six Blue Danios is 60 litres (16 gal). That is genuinely the lower bound: Blue Danios are energetic open-water swimmers that spend most of their time in the middle column, darting in formation across the length of the tank. A longer, shallower footprint — such as a standard 60 cm or 90 cm “breeder” layout — serves them far better than an equal-volume tall tank.
Because they are a shoaling species, the tank size should be calculated around a group, not an individual. A shoal of eight to ten fish, which is where behaviour and colour really come alive, is more comfortable in a 80–100 L (21–26 gal) setup.
Decor should balance open swimming lanes with planted margins. Fine-leafed plants such as hornwort, java moss, water wisteria or thin-stemmed stem plants along the sides and back give the fish cover and make them bolder; leaving the centre clear allows the shoal to do what it does best. A tight-fitting lid is non-negotiable — Blue Danios are fast and will jump if startled or if the water level is too close to the rim.
What water parameters do Blue Danios need?
Blue Danios are among the more tolerant cyprinids in the hobby, but that tolerance is not an invitation to neglect stability.
- Temperature: 21–26 °C (70–79 °F). They tolerate the cooler end better than most tropical fish, making them compatible with species that dislike high heat, but sustained temperatures below 20 °C should be avoided.
- pH: 6.5–7.5. Soft to neutral water is ideal and matches their native streams.
- Hardness: 5–15 dGH. They are not demanding on hardness, and moderately hard tap water in the 10–15 dGH range works fine in most regions.
Weekly partial water changes of 20–25% and a reliable filter rated for the tank volume are the backbone of good maintenance. Stable, clean water matters far more than chasing precise numbers.
What do Blue Danios eat?
Blue Danios are omnivores and genuinely unfussy feeders. In the wild they take insects, small invertebrates, algae and plant matter at or near the surface; in the aquarium they accept almost any appropriately sized food offered.
A quality micro-pellet or small flake makes a practical staple. Rotating in small live or frozen foods — daphnia, brine shrimp, micro-worms or finely chopped bloodworm — brings out the best colour and conditions fish for breeding. Feeding small amounts once or twice a day is sufficient; Blue Danios have fast metabolisms but are not greedy in the way that can quickly foul water. Remove uneaten food after a few minutes.
Variety is the main principle. A fish fed only one dry food will survive; a fish fed a rotation of flake, pellet and small live or frozen foods will look noticeably better and breed more readily.
Are Blue Danios peaceful — and what fish can live with them?
Blue Danios are entirely peaceful and one of the better-behaved community fish available. They pose no threat to similarly sized or larger tank-mates, do not nip fins, and their fast movement around the middle column does not disturb bottom-dwellers or slower surface fish.
The main consideration when building a community around Blue Danios is their own wellbeing: they need a shoal of at least six, ideally more, to feel secure and display natural behaviour. A too-small group produces timid, washed-out fish that hide. Good companions include other peaceful small cyprinids (cherry barbs, ember tetras, harlequin rasboras), dwarf corydoras and other small bottom-dwellers, peaceful livebearers such as endlers or guppies, and small labyrinth fish that are not aggressive. Avoid pairing them with large, predatory or highly nippy species.
For a full list of compatible and incompatible species, see Blue Danio tank mates.
How do you tell male from female Blue Danios?
Blue Danios show moderate sexual dimorphism that becomes easier to read as the fish mature.
Females are noticeably rounder in the belly, especially when in spawning condition, and are typically slightly larger overall. Their colouration is still attractive but tends toward a softer, less saturated blue.
Males are more slender and streamlined throughout, and in good health show a brighter, more intense powder-blue on the flanks. The pinkish-yellow lateral stripes are present in both sexes but often appear sharper on males.
In a healthy, well-fed mixed-sex group the difference in body shape between a gravid female and a slim male is usually the easiest indicator, particularly when viewed from above.
How do Blue Danios breed?
Blue Danios are egg scatterers — they broadcast adhesive eggs over fine-leafed plants or substrate during a brief, energetic spawning chase, and then pay no further attention to the eggs or fry. Both parents will readily eat the eggs given the chance, so any deliberate breeding effort requires separating eggs from adults promptly.
A basic breeding setup involves a small (20–40 L) bare-bottomed or mesh-floored tank with a gentle sponge filter, bunches of java moss or a synthetic spawning mop, and well-conditioned adults fed live or frozen foods for one to two weeks prior. Spawning is often triggered by a slight temperature rise toward the upper end of their range or by a morning of brighter light. After spawning, remove the adults.
Eggs typically hatch in two to three days at 24–26 °C (75–79 °F). Fry are small and require infusoria or commercial fry food initially, transitioning to baby brine shrimp as they grow. The species is rated medium difficulty mainly because of the need for a separate breeding setup and the challenge of rearing fry on suitably fine foods — the spawning act itself is straightforward once the fish are in condition.
What are common Blue Danio diseases?
Blue Danios are hardy fish and, in a properly maintained tank, rarely succumb to disease. The most common problems encountered are shared with most small cyprinids:
Ich (white spot disease) — the classic white salt-grain spots, usually appearing after a temperature drop, introduction of a new fish without quarantine, or shipping stress. Raising the temperature gradually to the upper end of their range and maintaining excellent water quality aids recovery; prevention is the more reliable strategy.
Velvet (Oodinium) — a dusty gold or rust-coloured sheen on the body, often accompanied by scratching against surfaces and rapid gill movement. More dangerous than ich and can move through a tank quickly.
Fin rot — ragged or receding fin edges, almost always linked to poor water quality. Improving water conditions is the first and most important step.
Internal parasites and bacterial infections can occur in fish imported under stress; a four-week quarantine for all new additions is the single most effective prevention measure.
Health note: medication dosing and disease diagnosis are outside the scope of a care guide. If you suspect illness, confirm the symptoms against a reputable veterinary or specialist fish-health source before medicating — incorrect treatment can cause more harm than the original condition.
How long do Blue Danios live?
In good aquarium conditions Blue Danios live 3 to 5 years. The lower end of that range is more common when fish are kept in marginal conditions — inadequate group size, fluctuating temperatures or poor water quality all accelerate wear. Fish that are housed in a properly sized, heated, filtered tank with a stable diet and a shoal large enough to feel secure regularly reach the upper end of that range.
Because Blue Danios are inexpensive and widely available, there is a temptation to treat them as disposable. Provided the basic requirements are met, however, they are genuinely long-lived little fish, and a well-established shoal that has been together for several years — fully coloured, confident and moving in tight formation — is one of the more rewarding sights in a community tank.
Frequently asked questions
How many Blue Danios should I keep together?
At least six — ideally eight or more. Blue Danios are shoaling fish that feel secure and display their best colour in tight groups. A lone or paired fish will be timid, washed-out and prone to stress.
Are Blue Danios the same as Zebra Danios?
No. Both are Danio species and share a similar body shape, but Danio kerri (Blue Danio) is smaller, powder-blue with pinkish-yellow lateral stripes, and originates from southern Thailand — quite different from the bold horizontal blue-and-silver stripes of the Zebra Danio (Danio rerio).
What you need to keep a blue danio
The baseline is a heated, filtered 60 L+ tank: a reliable heater to hold 21–26 °C (70–79 °F), a gentle filter that won't batter a blue danio in the current, and a tight-fitting lid. Cycle the tank fully before adding any fish.
As an Amazon Associate we earn from qualifying purchases — buying through these links costs you nothing extra.
