Can otocinclus live with black ghost knives?

Verdict

No. Otocinclus and black ghost knives should not share a tank. An adult black ghost knife eats fish that fit in its mouth, and at 2 inches otocinclus do.

Otocinclus72–79°F · pH 6–7.5

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 2 inches otocinclus do.
Watch outBlack ghost knives grow to 15 inches and need 125 gallons, far more than a tank set up for otocinclus.

What works

Both are fine at 73–79°F.
pH 6–7.5 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

	Otocinclus	Black ghost knife
Temperature	72–79 °F	73–82 °F
pH	6–7.5	6–8
Adult size	2.0 in	15.0 in
Minimum tank	20 gal	125 gal
Temperament	Peaceful	Semi-aggressive
Swims at	Bottom	Bottom
Group	Groups of 6+	One per tank
Diet	Herbivore	Carnivore

Better tank mates for otocinclus

All otocinclus tank mates

Better tank mates for black ghost knives

All black ghost knife tank mates

Questions

Can otocinclus live with black ghost knives?

No. Otocinclus and black ghost knives should not share a tank. An adult black ghost knife eats fish that fit in its mouth, and at 2 inches otocinclus do.

What temperature suits both otocinclus and black ghost knives?

73–79 °F. Otocinclus need 72–79 °F, black ghost knives need 73–82 °F.

What size tank do otocinclus and black ghost knives need together?

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