Can koi live with pencilfish?

Verdict

No. Koi and pencilfish should not share a tank. Koi are coldwater animals (59–77°F); pencilfish need 75–82°F. They overlap only at 75–77°F, the edge of both ranges.

Koi59–77°F · pH 7–8.5

Pencilfish75–82°F · pH 5–7.5

What to watch

Deal breakerKoi are coldwater animals (59–77°F); pencilfish need 75–82°F. They overlap only at 75–77°F, the edge of both ranges.
Watch outAt 24 inches a koi can swallow a small pencilfish. Fast, alert fish usually stay out of reach.

What works

pH 7–7.5 suits both.

Water side by side

The green band is the temperature range both can live in.

The green band is the pH both tolerate.

Size to scale

Adult length in an aquarium. A fish can swallow anything that fits in its mouth, roughly a third to half its own length for predators.

Care at a glance

	Koi	Pencilfish
Temperature	59–77 °F	75–82 °F
pH	7–8.5	5–7.5
Adult size	24.0 in	2.0 in
Minimum tank	Pond	15 gal
Temperament	Peaceful	Peaceful
Swims at	All levels	Middle
Group	Groups of 3+	Groups of 6+
Diet	Omnivore	Omnivore

Better tank mates for koi

All koi tank mates

Better tank mates for pencilfish