Black Ghost Knifefish

Apteronotus albifrons

Also known as: Black ghost knife, BGK

Water Parameters

• Temperature: 23–28°C
• pH: 6–7.5
• Hardness (GH): 36–179 ppm (2–10 dGH)

Values above are general hardness (GH). For carbonate hardness (KH), the buffer that keeps pH stable, see the water parameters guide.

Care Summary

The capstone oddity of the freshwater hobby: a knifefish with no dorsal fin and a single long undulating ribbon of an anal fin that lets it glide forwards, backwards, and hover in place, all in a velvety jet-black body crossed by two white rings near the tail. The black ghost is weakly electric, generating and sensing a field it uses to navigate and hunt in darkness, and it can become remarkably tame, learning to take food from the hand. It is also a serious commitment: it grows to around 45cm, lives well over a decade, and is a scaleless, sensitive, nocturnal predator that needs pristine water, dim light, a daytime hiding place, and a tank measured in hundreds of litres, and it must not be housed with fish small enough to eat or aggressive enough to bully it. Bought on impulse as a charming 10cm juvenile it almost always ends badly; given the large, calm, mature setup it truly needs, it is one of the most rewarding and characterful fish a keeper can own.

Tankmates

A peaceful giant toward fish it cannot eat, but two cautions define its stocking. First, it is a nocturnal predator: small fish (neons, guppies, small rasboras) and shrimp will be hunted and eaten in the dark, so tankmates must be too large to swallow. Second, it is scaleless and territorial toward its own kind and other knifefish, and it is easily bullied or damaged by boisterous, aggressive, or fin-nipping tankmates, so it does best with large, calm, non-aggressive companions: silver dollars, bala sharks, larger peaceful catfish, denison barbs, and the like. It navigates and hunts using a weak electric field rather than sight, so it appreciates dim lighting, a cave or tube to shelter in by day, and pristine, well-oxygenated water (it is sensitive to poor conditions and to copper). Its eventual size, around 45cm, makes a very large tank non-negotiable.

Compatible with

• Silver Dollar
• Bala Shark
• Common Pleco
• Bristlenose Pleco
• Denison Barb

Avoid keeping with

• Betta
• Neon Tetra
• Guppy
• Cherry Shrimp
• Oscar
• Large Cichlids

Common Problems

• outgrowing the tank (reaches around 45cm)
• predation on small tankmates and shrimp
• sensitivity to poor water quality and copper as a scaleless fish
• being bullied or damaged by aggressive tankmates

Sources: seriouslyfish.com, fishbase.org · Last updated: 2026-06-20