Black Ghost Knifefish

Apteronotus albifrons

Also sold as BGK

Black Ghost Knifefish (Apteronotus albifrons) is a semi-aggressive freshwater fish that reaches about 50 cm (19.7 in) and swims in open water. It wants 73–82°F (23–28°C) and pH 6–8, can be kept singly, and needs a tank of at least 454 L (120 gal).

At a glance

Type	Fish
Adult size	50 cm (19.7 in)
Minimum tank	454 L (120 gal)
Group size	Can be kept singly
Temperature	73–82°F (23–28°C)
pH	6–8
Temperament	Semi-aggressive
Lifespan	10–15 years
Eats shrimp	Yes

Before it goes in

Black Ghost Knifefish needs at least 454 L (120 gal). The smallest size in this library that clears that is the 125 Gallon.
It eats small fish and shrimp — anything under about 16.7 cm (6.6 in). In this library that means Cherry Shrimp, Rummy Nose Tetra and Crystal Red Shrimp.
It holds at 73–82°F (23–28°C). That shares a window with Betta and Cherry Shrimp.
It is semi-aggressive — plan the tank around it rather than adding it to a finished community.
One of them takes up roughly 41% of what a 125 Gallon will comfortably hold, so plan the rest of the stock around it.

What tank size does it need?

At least 454 L (120 gal). The smallest size here that clears it is the 125 Gallon.

Will it eat shrimp?

Yes. Shrimp are food to it, so pick one or the other.

What water does it want?

73–82°F (23–28°C), pH 6–8.

How long does it live?

10–15 years in a tank that suits it. That is how long you are signing up for.

Good tank mates

Tank mates from this library that share its temperature window, are peaceful and eat neither it nor its young: Goldfish, Bristlenose Pleco, Celestial Pearl Danio, Molly and Otocinclus.
Plants that hold up with it: Hygrophila corymbosa 'Siamensis', Water Sprite, Anubias nana 'Petite' and Cryptocoryne wendtii.

Often compared with

	Black Ghost Knifefish	Black Skirt Tetra	Black Ruby Barb
Adult size	50 cm	6 cm	5.5 cm
Min tank	454 L	68 L	72 L
Group	1+	12+	6+
Temperature	73–82°F (23–28°C)	68–79°F (20–26°C)	68–81°F (20–27°C)
Eats shrimp	Yes	Yes	Shrimplets only

More livestock

Plan a tank with Black Ghost Knifefish →

Sources (6) · checked Sep 2026