Glass knifefish
Eigenmannia virescens
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
- Swim level
- Bottom
- Difficulty
- Difficult
- Breeding
- No record
- Rarity
- Very rare
- Origin
- South America
- Family
- Sternopygidae
Overview
The glass knifefish is a translucent, night-active fish that shelters among plants and wood by day and forages low in the tank after dark. It is best kept one to a tank unless the aquarium is very large, since it can be territorial toward its own kind, and it should have calm tankmates too big to be eaten. Feed live and frozen foods such as bloodworms, blackworms, and small shrimp in the evening. It has soft, scaleless skin, so provide fine substrate, gentle flow, and clean, stable water. This fish grows long and needs a tank of at least 320 liters.
In the wild
Eigenmannia virescens is found through much of tropical South America, in slow rivers, floodplain lakes, and dense marginal vegetation, often among floating plant roots and submerged wood. It prefers warm, softly flowing, well-shaded water. Recreate this with plenty of cover, subdued lighting, fine sand, and steady filtration. Keep the temperature between 23 and 28 degrees Celsius and the pH slightly acidic to neutral, from about 6 to 7.5.
Good to know
The glass knifefish belongs to Sternopygidae and takes its name from its see-through body, through which the backbone is visible. Males grow to around 45 centimeters, larger than females. Like other South American knifefish it swims with a long, rippling anal fin and is weakly electric, generating a steady electric field from a tail organ that lets it sense and communicate in the dark. Aquarium spawning is seldom recorded.
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, which it shifts in frequency to avoid jamming the signals of nearby knifefish.
Where to buy
Some links may not be the exact species or variety.
- LiveAquaria Freshwater and saltwater fish, inverts and corals
- The Wet Spot Tropical Fish Large freshwater selection from a longtime Portland fish store
…or ask your local fish store.
Appears in
Freshwater fish · Advanced fish · Bottom dwellers · Monster fish
Keeping Glass knifefish?
Track water tests, reminders and stocking fit.
Related species
Sailfin pleco
Pterygoplichthys disjunctivus17.7 in (45 cm)100 gal (380 L)73–84°F (23–29°C)
Sun catfish
Horabagrus brachysoma17.7 in (45 cm)170 gal (645 L)73–77°F (23–25°C)
Royal pleco
Panaque nigrolineatus16.9 in (43 cm)125 gal (473 L)72–82°F (22–28°C)
Common pleco
Hypostomus plecostomus15.7 in (40 cm)85 gal (320 L)72–86°F (22–30°C)
Ornate bichir
Polypterus ornatipinnis21.7 in (55 cm)172 gal (650 L)77–82°F (25–28°C)
Senegal bichir
Polypterus senegalus13.8 in (35 cm)143 gal (540 L)75–82°F (24–28°C)