How Many Zebra Danios in a 40 Gallon Tank?
About 17–21 — based on adult size, bioload, and real water volume.
About 17–21 zebra danio
Photo via Wikimedia Commons
In a 40-gallon tank you can comfortably keep about 17–21 zebra danio — enough for a proper school, on their own with good filtration and regular water changes. Add fewer if you're mixing in other species.
How we get that number
An adult zebra danio reaches about 2.0" and has a low bioload. Working from real water volume and waste output (not the old one-inch-per-gallon myth), a 40-gallon tank supports roughly 17–21 of them. Because zebra danio are schooling fish, keep them in a group of at least 6 — never just one or two. They need 64–77°F water at pH 6.5–7.5.
Build your exact stocking with the calculator → Full zebra danio care guide →
Gear for a 40-gallon tank
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FAQ
How many zebra danio can I keep in a 40 gallon tank?
About 17–21 zebra danio, kept on their own with good filtration. Add fewer when combining with other species — use the stocking calculator to be sure.