TankBud

Glass knifefish

Eigenmannia virescens

Also known as Transparent Knife

FreshwaterFish

Glass knifefish (Eigenmannia virescens)
Luis Ruiz Berti · CC BY-SA 3.0

Care at a glance

Temperature
73–82°F
23–28°C
pH
6.0–7.5
Adult size
17.7 in
45 cm
Minimum tank
85 gal
320 L
Temperament
Mostly peaceful
Social behavior
Solitary
Tankmates
With caution
Swim level
Bottom
Diet
Carnivore
Difficulty
Difficult
Breeding
No record
Rarity
Very rare
Family
Sternopygidae
Origin
South America

Overview

The glass knifefish is a long, translucent knifefish that needs a large tank with plenty of cover. It is best left to experienced keepers.

Did you know

The glass knifefish is nearly transparent, so its spine and internal organs show through its body. It also broadcasts a constant, weak electric field, shifting its frequency to avoid jamming the signals of nearby knifefish.

Caring for the glass knifefish

The glass knifefish grows long and needs a tank of at least 85 gal (320 L). It shelters among plants and wood by day, so give it plenty of cover and subdued lighting. It has soft, scaleless skin, so use fine sand and keep the flow gentle.

Keep the water clean and stable, with steady filtration. Hold it at 73 to 82°F (23 to 28°C) with a pH of 6.0 to 7.5.

The glass knifefish is active at night and forages low in the tank after dark. Feed it in the evening with live and frozen foods such as bloodworms, blackworms and small shrimp.

Keep one glass knifefish to a tank unless the tank is very large, since it can be territorial toward its own kind. It is mostly peaceful with other fish, but give it calm tank mates too big to be eaten. Males grow larger than females. Aquarium spawning is seldom recorded.

Good to know

The glass knifefish belongs to the family Sternopygidae and takes its name from its see-through body. Like other South American knifefish, it swims with a long, rippling anal fin. An organ in its tail generates the electric field it uses to sense and communicate in the dark.

In the wild

The glass knifefish is found through much of tropical South America, in slow rivers, floodplain lakes and dense marginal vegetation. It often lives among floating plant roots and submerged wood, in warm, softly flowing, well-shaded water.

Common questions

What size tank does a glass knifefish need?

A glass knifefish needs at least 85 gal (320 L). It spends most of its time in the bottom.

What temperature and pH does a glass knifefish need?

A glass knifefish is comfortable at 73–82°F (23–28°C) with a pH of 6.0–7.5.

What does a glass knifefish eat?

A glass knifefish eats live and frozen foods such as bloodworms, blackworms and small shrimp. Feed it in the evening, since it forages after dark.

How big does a glass knifefish get?

An adult glass knifefish reaches about 17.7 in (45 cm).

How can you tell a male glass knifefish from a female?

Males grow to a larger size than females do.

Related species