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Black Ghost Knifefish


Dear Aquaworld,

We have a black knife fish. Do they eat other fish?  We keep noticing a depletion of our guppies! Especially babies.  He is about 5 inches long.

Winter Garden, Florida, USA


Dear Julie,

Juv. Black Ghost Knife Fish

A 4 inch (10 cm) juvenile Black Ghost Knifefish (Apteronotus albifrons).

If the fish in question is what is commonly called the Black Ghost Knifefish (Apteronotus albifrons), yes they will eat small fish including guppies. This fish is primarily nocturnal and will eat fish while they sleep.  Also these fish can get quite large, over 18 inches (45 cm), and it is recommended that they be housed in an aquarium that is 120 gallons (456 l) or larger.

Good Luck!

Tony Griffitts

Published - 20070727