Zebra Danio
Fish
The tireless little striped torpedo that never stops commuting!
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🤓 Did you know? Zebra danios, known to scientists as zebrafish, are the most widely used non-mammalian vertebrate model organism in developmental biology and genetics research. Their embryos develop transparently outside the mother's body within hours of fertilization, letting researchers watch organs form in real time, and roughly 70 percent of human genes have a working counterpart in the zebrafish genome, sequenced in full in 2013. That same genetic malleability is also how GloFish, the first genetically modified animal ever sold as a pet, came to exist: they're fluorescent zebra danios.
🗓️ The first week
The numbers a new owner needs in the first week, each from the article it links to. Rows with no link come from the encyclopedia.
- How many
- At least 6, and 8 to 10 is the better start. In a small group the nipping lands on the same fish over and over; a larger one spreads it out.Handling guide →
- Tank size
- A 10-gallon works for the bare minimum school of 6. A 20-gallon long is the better minimum for 8 to 10, and long beats tall: danios in a short tank run laps.Setup guide →
- Heater
- Optional at 64 to 77°F, which is room temperature in most homes. Add one if the room runs cool or tropical tankmates need warmer, steadier water.Setup guide →
- Water chemistry
- pH 6.0 to 8.0 and hardness anywhere from about 90 to 357 ppm. Ammonia and nitrite still read zero before stocking.Setup guide →
- Filtration and flow
- Turnover 4 to 5 times the volume an hour, sponge or hang-on-back, with the outlet aimed along the tank so there is a fast end and a slow end.Setup guide →
- The lid
- They jump 20 to 30 cm, and a small gap in the hood is enough. A tight lid is not optional.Setup guide →
- Planting
- Substrate and live plants, not bare glass. Plant the sides and back and leave the middle open, so there is cover and somewhere to sprint.Enrichment guide →
- Feeding
- Twice a day, what the school finishes in two to three minutes.Feeding guide →
- Fry you did not plan
- Daily live or frozen food is what triggers spawning. Keep it an occasional treat if you do not want fry.Feeding guide →
- Acclimation
- Float the sealed bag 15 to 20 minutes, then a quarter cup of tank water every 5 minutes for another 15 to 20. The bag water goes down the drain, not in the tank.Handling guide →
- Quarantine
- Two to four weeks in a 10 to 20-gallon bare tank with its own sponge filter and heater. It doubles as the hospital tank later.Handling guide →
- Budget
- $2 to $3 a fish, about $12 to $30 for the school; GloFish are the same species at about $8 each. Most first setups land around $100 to $180.Cost guide →
- Lifespan
- Around 3.5 years, up to 5.5 with excellent care.Cost guide →
- Adult size
- 1.5 to 2.5 inches (4 to 6 cm); occasionally to 3 inches (7.5 cm) in captivity.
- Mycobacteriosis
- Lethargy, emaciation, ulcers and pale patches, with no reliable cure once visible. It can infect people through a cut, so gloves for tank maintenance if you have one.Health guide →
- Water chemistry, the wider picture
- KH holds pH in place, and dosing pH-up or pH-down against it is how keepers crash a tank. Test the source water and work with what it gives you.Freshwater pH, GH, and KH →
- Water changes
- 25 to 30% weekly from the substrate, with conditioned water at tank temperature. Test nitrate first: under 20 ppm the routine is right, past 40 ppm the next change is 50%.Aquarium Water Changes →
- Power outage
- Oxygen is the threat, not darkness. Unplug the filter rather than letting it sit dead in the water, and keep the surface moving.Power outage guide →
🚨 Emergency card
Test the water first, then act on these today. Aquatic vets are rare, so nearly all of this is handled at home.
- Small white spots like grains of salt, extra mucus, flashing, rapid breathing: ich, treated with a gradual temperature rise plus ich medication and daily partial water changes
- Fin edges discoloring, then fraying: fin rot, treatable
- Floating at the surface unable to swim down, or struggling to rise
- Lethargy, appetite loss, and emaciation, with ulcers, pale patches, or white nodules: mycobacteriosis, no reliable cure once visible
A slow-growing, sometimes painful bump on your own skin after tank work is a doctor's visit; the same bacterium infects people through cuts.
📰 Where to go next
How Much Does Zebra Danio Ownership Really Cost?
$2 a fish, $100 to $180 for a first setup, and why GloFish cost four times as much for identical care.
Zebra Danio Tank Setup: The Rare Community Fish That Might Not Need a Heater
The 90x30cm footprint, 64 to 77F, and the rare community fish that might not need a heater.
Zebra Danio Feeding: Diet, Schedule, and the Live Food That Can Trigger an Accidental Spawn
Twice a day, two to three minutes, and the live food that triggers an accidental spawn.
Zebra Danio Handling: Why the Easiest Fish to Keep Is One of the Hardest to Catch
Trap and guide rather than chase, float-and-drip timings, and the school size that matters more than technique.
Common Zebra Danio Health Issues, Backed by the Best-Documented Fish Disease Data in the Hobby
Ich, fin rot, swim bladder, and the fish tuberculosis this species is studied for.
Zebra Danio Enrichment: The Most Studied Fish in the World Lives in a Bare Box
The enrichment study that measured survival rather than behavior, and why a cube is the wrong tank.
🛒 What to buy
Prices and the reasoning behind each item are in How Much Does Zebra Danio Ownership Really Cost?.
❓ Frequently Asked Questions
What size tank does a school of zebra danios need?
A 10-gallon tank is workable for the bare minimum school of 6. Seriously Fish's recommended footprint, roughly 90x30cm even for a small group, lines up closely with a 20-gallon long tank, a better practical minimum for the fuller 8 to 10 fish school most sources recommend.
Do zebra danios need a heater?
Not strictly. Multiple care sources put their comfortable range at 64 to 77°F, close enough to room temperature in most homes that a heater is optional. It's still worth adding if your home runs cool or if danios share a tank with tropical fish that need warmer, more stable water.
How many zebra danios should I keep together?
At least 6. Aquarium Co-Op names 5 to 6 as the workable minimum, but Seriously Fish recommends starting with 8 to 10 or more for natural schooling behavior. A group that's too small is more likely to direct fin-nipping energy at tankmates instead of schooling normally.
📚 Encyclopedia
Zebra Danio
Danio rerio
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📰 Deep Dive
🐠 How Much Does Zebra Danio Ownership Really Cost?
🐠 Zebra Danio Handling: Why the Easiest Fish to Keep Is One of the Hardest to Catch
🐠 Common Zebra Danio Health Issues, Backed by the Best-Documented Fish Disease Data in the Hobby
🐠 Zebra Danio Tank Setup: The Rare Community Fish That Might Not Need a Heater
🐠 Zebra Danio Feeding: Diet, Schedule, and the Live Food That Can Trigger an Accidental Spawn
🐠 Zebra Danio Enrichment: The Most Studied Fish in the World Lives in a Bare Box
🩺 Health and More
🐠 Aquarium Power Outages, Transport, and Moving Your Fish: The Complete Plan
🦠 How to Cycle a Fish Tank, Start to Finish: Fishless and Fish-In
🧽 Aquarium Filtration: How It Actually Works and How to Maintain It
🪣 Aquarium Water Changes: How Much, How Often, and What the Number Is For
🐟 Aquarium Stocking and Tankmates: How Many Fish, and Which Ones Go Together
🧪 Freshwater pH, GH, and KH: Why Chasing a Number Backfires
🩺 Fish Quarantine and Treatment: The Hospital Tank Guide
🩹 Treating Ich: Heat, Salt or Medication, and the Temperature Ceiling That Decides
🩺 How to Tell If Your Fish Is Sick: Waste, Behavior, and Body Signs
🧊 Cooling an Aquarium Without a Chiller
🐠 Four Fish, Four Completely Different Difficulty Levels
🤩 Fun Facts
🐠 The Fish Behind GloFish
The fluorescent GloFish sold in pet stores are zebra danios with a jellyfish-derived fluorescent gene added to their genome. That gene wasn't developed to be sold as a pet at all, researchers at the National University of Singapore originally built it to create a fish that would glow in the presence of water pollutants, and it only later got licensed for the aquarium trade.