Can paradise fish live with black ghost knives?

Verdict

No. Paradise fish and black ghost knives should not share a tank. An adult black ghost knife eats fish that fit in its mouth, and at 3.5 inches paradise fish do.

Paradise fish61–79°F · pH 6–8

Black ghost knife73–82°F · pH 6–8

What to watch

Deal breakerAn adult black ghost knife eats fish that fit in its mouth, and at 3.5 inches paradise fish do.
Watch outBlack ghost knives grow to 15 inches and need 125 gallons, far more than a tank set up for paradise fish.

What works

Both are fine at 73–79°F.
pH 6–8 suits both.
They use different parts of the tank: paradise fish the top, black ghost knives the bottom.

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

	Paradise fish	Black ghost knife
Temperature	61–79 °F	73–82 °F
pH	6–8	6–8
Adult size	3.5 in	15.0 in
Minimum tank	20 gal	125 gal
Temperament	Semi-aggressive	Semi-aggressive
Swims at	Top	Bottom
Group	One per tank	One per tank
Diet	Omnivore	Carnivore

Better tank mates for paradise fish

All paradise fish tank mates

Better tank mates for black ghost knives

All black ghost knife tank mates

Questions

Can paradise fish live with black ghost knives?

No. Paradise fish and black ghost knives should not share a tank. An adult black ghost knife eats fish that fit in its mouth, and at 3.5 inches paradise fish do.

What temperature suits both paradise fish and black ghost knives?

73–79 °F. Paradise fish need 61–79 °F, black ghost knives need 73–82 °F.

What size tank do paradise fish and black ghost knives need together?

At least 125 gal, set by the black ghost knife. Add space for each extra fish.