Can a guppy live with fancy goldfish?

No.

Fancy goldfish need cool water; guppies need tropical water.

Why it doesn’t work

Fancy goldfish do best in cool water (65–74°F), while guppies need tropical water (72–82°F), so there's almost no temperature that suits both for long. Keeping goldfish warm shortens their comfort and stresses them, and keeping guppies cool weakens them. On top of that, an adult fancy goldfish grows to 6–8 inches and may eat guppies that are only 1.5–2.5 inches.

If they’re already together

1. Move the guppies to their own tank as soon as you can, since they are the ones at risk of being eaten and the ones most affected by cool water. A group of at least 3 guppies, with several females to each male, will do better apart.
2. While you set up the second tank, keep the water temperature in the small overlap of 72–74°F and watch for guppies being chased, hiding constantly, or going missing.
3. Make sure the goldfish tank is at least 20 gallons and well established, because fancy goldfish should only be kept in a mature tank, and keep the guppy tank at 10 gallons or more.

Instead: Keep fancy goldfish in their own cool-water tank of 20 gallons or more, and give guppies a separate tropical tank of at least 10 gallons. Both species like pH 7.0–8.0 and hard water, so the water chemistry is easy to match, but each needs its own temperature.

How we reached this verdict

Side by side

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