The zebra danio is a small, fast minnow from the streams and floodplains of South Asia, marked with horizontal blue-gold stripes.
Widely used as a laboratory model organism, it is one of the hardiest and most adaptable aquarium fish available.
It is an excellent beginner species, tolerant of a wide temperature range including cooler rooms.
Avoid dyed or hybrid colour variants where possible, and never keep it in a tiny tank, as its constant activity demands swimming space.
Housing
Keep a shoal of at least six in 75 litres (20 gallons) or more, well filtered.
They thrive at 18-24C and do not strictly need a heater in a stable, room-temperature home, which suits unheated setups in temperate climates.
These are powerful, restless swimmers that need length rather than height for laps along the tank.
They tolerate a wide range of water chemistry and appreciate some current and a secure lid, as they are accomplished jumpers.
Diet
Zebra danios are opportunistic omnivores that feed at the surface and in midwater.
A quality flake or micro-pellet works as the staple, supplemented with frozen or live daphnia, brine shrimp and bloodworm for variety.
Feed small amounts once or twice daily, only what is taken in a minute or two.
Their fast metabolism and constant activity mean they rarely refuse food, so portion carefully to avoid overfeeding and fouling the water.
Health
Danios are robust and disease-resistant, with most ailments arising from overcrowding, poor water quality or excessive heat rather than the fish themselves.
Ich and fin rot are the usual concerns and clear readily with corrected conditions.
Keeping them too warm for long periods can shorten their lifespan, so avoid over-heating the tank.
Quarantine new arrivals, maintain weekly partial water changes, and fit a tight lid, since stress can prompt jumping.
Temperament
Active, peaceful and confident, zebra danios shoal loosely and dash around the upper levels of the tank.
Their speed and constant motion can unsettle very timid or slow species in a community.
They can nip long, flowing fins when understocked, so keep six or more to channel that energy within the group.
Pair them with similarly active, sturdy fish rather than delicate or long-finned tankmates such as bettas or fancy guppies.
A good fit for
Beginners wanting a tough, lively first fish
Unheated, room-temperature aquariums
Active community tanks with sturdy species
Keepers who enjoy constant movement
Common mistakes to avoid
Cramped tanks restricting their fast swimming
Keeping them too warm, shortening lifespan
Fin-nipping when kept in too-small groups
Open tanks they readily jump out of
Is your enclosure big enough?
Minimum volume75 litres (20 US gallons)
CompanyCannot be kept alone. The minimum is 6, and the space above is for that group.
In a fish tank the patient is usually the water. Test before you treat — dosing a healthy tank for a disease it does not have makes things worse.
Go now
Any detectable ammonia or nitrite in a stocked tankLarge water change now with dechlorinated, temperature-matched water. Stop feeding. Test again in 12 hours. Both are directly toxic. How toxic the ammonia reading is depends on pH and temperature, so the same number can be harmless or lethal.
Now
Fish gasping at the surface, or crowding the filter outflowIncrease surface agitation immediately, then test the water. Either the oxygen has crashed or the gills are being chemically burned. Both are hours-scale problems.
Now
Sudden deaths, more than one fish in a dayTest ammonia, nitrite, nitrate and temperature before doing anything else. Do not add medication yet. Multiple simultaneous deaths point at the water or the equipment, not at a pathogen.
Now
Today
Flashing — repeatedly scraping against decor or substrateTest the water, then look closely for parasites. Irritation is either chemical or parasitic; the test tells you which before you medicate.
Today
White salt-grain spots over the body and finsBegin the appropriate treatment today and check the temperature. The parasite's life cycle is temperature-driven, and it multiplies with every cycle you wait.
Today
Soon
Clamped fins, hiding, or refusing food for more than two daysTest the water and review recent changes. Usually the earliest visible sign of a parameter drifting.
A few days
Never add a new fish to a tank that is not fully cycled, and never treat blind. A test kit is cheaper than the fish.
This is general guidance for a healthy adult, not a diagnosis. An exotics vet who knows your animal always overrides it — and the time to find one is before you need one.
What it really costs
Setup, monthly, first year and across a whole life, itemised and with the electricity worked out from the actual wattage. Published figures for the same animal disagree by a factor of four, so the calculator shows ranges rather than picking one.
Intermediate
Beginner
Beginner
Beginner
Beginner
Beginner