Species · Danios & minnows
Zebra Danio
Danio rerio
The bulletproof striped starter fish — hardy, active, and forgiving. Just give it a real group and horizontal swimming room, and keep it on the cooler side; it can nip if kept in too small a group.
Difficulty: BeginnerTropical community tank✓ Fact-checked care guide
Quick facts
| Adult size | ~5 cm / 2 in |
|---|---|
| Minimum tank | ~60 L / 15 US gal with length — SeriouslyFish recommends a 90 × 30 cm base |
| Temperature | 20–24 °C / 68–75 °F (a subtropical fish — likes it cooler; species range 18–25 °C / 64–77 °F) |
| pH | 6.0–8.0 |
| Hardness | 5–20 dGH (soft to moderately hard) |
| Filtration & flow | Cycled; tolerates and enjoys a bit more flow than most community fish |
| Diet | Omnivore — flake/small pellet plus small live/frozen foods |
| Social | Active shoaling fish — keep at least 6, ideally more |
| Temperament | Peaceful but very energetic |
| Lifespan | 3–5 years |
Overview
The zebra danio (Danio rerio) is the classic "can't-kill-it" first fish — hardy, endlessly active, and forgiving of the mistakes every beginner makes. (It is also a famous laboratory model animal.)
Two things people get wrong: it is a subtropical fish that likes it cooler than most tropicals, and it is a fast, energetic swimmer that needs a proper group and horizontal room — kept in too small a group it can turn to fin-nipping.
Water & tank
Danios are unfussy on chemistry (pH 6.0–8.0, 5–20 dGH) but prefer the cooler end — around 20–24 °C / 68–75 °F — and can even be kept unheated in a warm room. Don't keep them at high tropical temperatures.
They are speed-swimmers: give them length. At least ~60 L / 15 US gal with horizontal swimming space (SeriouslyFish recommends a 90 × 30 cm base), cycled, with a secure lid — they are jumpers.
Feeding
Omnivores that eat readily — a quality flake or small pellet base plus small live/frozen foods. They feed mostly in the upper water.
Feed small amounts once or twice a day.
Behaviour & tankmates
Peaceful in the sense of not being aggressive, but boisterous — keep them in a group of 6+ (more is better) to spread out their energy. Under-grouped danios are the ones that nip slow, long-finned tankmates.
Avoid pairing them with slow or long-finned fish (like a betta or fancy guppies); they suit other active, robust community fish.
What to expect
Instant activity — danios rarely sulk and usually eat and school from day one. Constant zippy swimming near the top is completely normal.
Myths, kindly busted
“Zebra danios need a warm tropical tank.”
They are subtropical and prefer it cooler (around 20–24 °C); high tropical temperatures are not ideal.
“Danios are fin-nippers.”
They mainly nip when kept in too small a group or with slow long-finned tankmates — a proper shoal of 6+ and suitable tankmates largely solves it.
When to act
We triage, not diagnose — but these are worth a closer look (starting with a water test):
- Fin-nipping or chasing — usually too small a group; increase the shoal and rehome unsuitable long-finned tankmates.
- Lethargy or gasping (unusual for such an active fish) — test the water immediately.
Sources & further reading
- SeriouslyFish — Danio rerio — Adult ~50 mm SL; recommended 90 × 30 cm base (needs swimming length); temperature 18–25 °C / 64–77 °F (subtropical); pH 6.0–8.0; hardness 5–20 dGH; very peaceful shoaling community fish.
Written & fact-checked by The Finfern Team against the sources above — kind, general guidance, not a diagnosis. If something looks wrong, test your water and, if it persists, contact a fish-savvy vet.
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