Freshwater Fish · Danios & Minnows

Zebra Danio

Danio rerio

Tireless striped swimmer for cooler tanksBeginner

Lifespan: 3-5 years
Size: 1.5-2 in
Social needs: Shoaler; keep 10+ together
Time: Low; daily feeding, weekly water change
Cost: Low
Diet: Omnivore; flakes, micro pellets, frozen foods

Overview

What is this animal?

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.

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.

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They can nip long, flowing fins when understocked, so keep ten 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

Enclosure

Minimum 21 gallons, for a group of 10

Cannot be kept alone. The minimum is 10, and the space above is for that group.

Keep a shoal of at least ten in a tank at least 36 in long holding 21 US gallons or more, well filtered.
Seriously Fish gives that length even for a small group, and the smallest standard US tank that long is a 30-gallon (36 x 12 x 16 in).
They thrive at 64-75°F and do not strictly need a heater in a stable, room-temperature home, which suits unheated setups in temperate climates.

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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.

Check your enclosure

Supplies

Setup

Tank and stand
Filter
Thermometer, plus a heater only if the room runs below the species' range
Substrate, plants and decor
Liquid test kit
Dechlorinator and starter supplies

Ongoing

Quality tropical flake or micro-pellet
Frozen daphnia
Frozen brine shrimp
Frozen or freeze-dried bloodworm (chopped fine; whole bloodworm is too large for celestial pearl danios)
Frozen cyclops or baby brine shrimp (for celestial pearl danios)

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Spirulina or vegetable flake
Small feeding spoon for measured pinches
Fine net for removing leftovers

Safe substrate: Fine, smooth sand · Smooth, rounded fine gravel (not for loaches or sand-sifting cichlids; sand is better for corydoras) · Bare bottom (quarantine and grow-out only)

Work out the cost

Care routine

Daily

Check temperature and equipment
Feed
Head-count and look everyone over

Every few days

Top up evaporationevery 3 days

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Weekly

Check the lid
Test the water
Water change and gravel vacuum
Wipe the front glass only

Every few weeks

Trim and thin the plantsevery 2 weeks

Monthly

Check supplies and reagent dates
Replace or recharge chemical media, if you use any (skip it in a blackwater tank)
Rinse the filter media

Health review: Quarterly temperature and stocking review, every 3 months

Tools

Is your enclosure big enough?Check your measurements against the recommended size What will it cost?Setup, monthly and over its whole life, itemised Is this ammonia reading dangerous?Works out the toxic part from your pH and temperature

Care in depth

Diet

Omnivore; flakes, micro pellets, frozen foods

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

Signs of good health, and the common problems

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: mild fin rot usually clears once water quality is corrected, but ich (white spot) is a parasite that needs prompt treatment as soon as the spots appear.

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.

Is this urgent?

6 warning signs and how fast to act, 3 of them right away

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 with fast gill movement, or crowding the filter outflowIncrease surface movement now (gently in a betta or gourami tank, without creating a strong current), then test the water. Either the oxygen has crashed or the gills are being chemically burned. Both are hours-scale problems. Bettas, gouramis and corydoras rise to gulp air as part of normal breathing; the warning is constant gulping, fast gill movement, or the whole group hanging at the top.

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 usually point at the water or the equipment rather than a pathogen, so rule those out first.

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.

Bedding and substrate

3 safe, 4 with a caveat, 2 to avoid

Substrate in an aquarium is a filter as much as a floor. Most of the biology lives in and on it.

Safe

Fine, smooth sandCorrect for corydoras, kuhli loaches, eartheaters such as rams and acaras, and anything else that sifts or burrows. Barbels wear away on sharp gravel.

safe

Smooth, rounded fine gravel (not for loaches or sand-sifting cichlids; sand is better for corydoras)Rinse thoroughly before use. Grain size should be too large to swallow and too small to trap food. Kuhli loaches need sand to burrow into and rams and acaras sift mouthfuls of it; bronze and panda corydoras manage on smooth fine gravel, but sterbai corydoras need sand.

safe

Bare bottom (quarantine and grow-out only)Legitimate for quarantine and grow-out tanks. Easy to clean, but it holds far less biological filtration, and it is no long-term home for burrowing loaches or sand-sifters.

safe

With a caveat

Crushed coral or aragoniteDeliberately raises hardness and pH. Correct for rift-lake cichlids, wrong for soft-water species.

with a caveat

Aquasoil for planted tanksExcellent for plants, but most active soils soften the water and pull pH and KH down for months, and many leach ammonia for the first weeks. Right for soft-water species; wrong for hard-water animals (livebearers, rainbowfish, goldfish, and snails, whose shells erode in soft, acidic water) unless you test GH and KH and remineralise. Cycle around it; do not stock into it.

with a caveat

Very deep sand bedsAnaerobic pockets form below about 2 inches in still sand. Either keep it shallow or keep it stirred.

with a caveat

Painted or coated gravelUsually fine, but coatings chip. Test a handful in a jar for a week first.

with a caveat

Never

Sharp or angular gravel with bottom-dwellersWears down barbels and leads to infection in corydoras and loaches.

never

Anything containing metal, limestone of unknown origin, or shells in a soft-water tankSlowly alters chemistry in ways that are hard to diagnose later.

never

This is our general list for freshwater fish. We have not built one specific to Danios & Minnows yet.

Top resources for more info

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