Glass Knifefish (Eigenmannia virescens) Care Guide
Eigenmannia virescens is a gregarious South American electric knifefish with a translucent green body that tolerates conspecifics.
Compiled by Aquairi from published sources · Published · Updated
Overview
Eigenmannia virescens, the glass or green knifefish, is a weakly electric freshwater fish of the family Sternopygidae from South America. The body is elongated and translucent green, and the species relies on electric organ discharge for species and sex recognition.
Taxonomy
- Family: Sternopygidae
- Genus: Eigenmannia
- Scientific name: Eigenmannia virescens
- Common synonym: Green Knifefish
Habitat
FishBase reports the species as widely distributed east of the Andes from the Orinoco to the La Plata basins, with Wikipedia adding records from the Magdalena basin to the Rio de la Plata. It prefers deep still waters in ponds and creeks over plant-debris substrate and reaches about 44 cm SL.
Tank requirements
- Minimum tank volume: 400 L
- Temperature: 24-28 °C (75-82 °F)
- pH: 6-7.5
- GH: 4-15 °dGH
- Group size: keep in groups of 4 or more
- Lifespan: 6-12 years
- Substrate: sand
Diet
The glass knifefish is a carnivore. It is fed once daily on meaty and live foods in the aquarium.
Compatibility
FishBase describes the species as gregarious, timid and nocturnal. Unlike the territorial Apteronotus knifefishes it tolerates conspecifics and is best kept in groups. It is peaceful and occupies the middle of the water column; suitable tankmates include larger tetras and Corydoras, while aggressive fish and tiny fry should be avoided.
Conservation status
IUCN Red List: Least Concern (assessed 2020).
Breeding the Glass Knifefish (Eigenmannia virescens)
Overview
The Glass Knifefish (Eigenmannia virescens) is a weakly electric, gregarious South American gymnotiform widely distributed east of the Andes from the Orinoco to the La Plata basins, reaching up to 44 cm SL. It inhabits deep still waters and creeks rich in plant debris and is nocturnal (FishBase). Unlike the territorial ghost knifefish, it is social and is one of the few knifefish reproduced in aquaria.
Sexing
Direct external sexing is unreliable; sexual recognition is electric. Males display increased electric-discharge amplitude during nighttime breeding competition, and the male's electric courtship signal is what identifies and stimulates a ripe female (FishBase).
Conditioning
FishBase records a fractional spawner with fecundity around 905 eggs released in successive batches. Conditioning relies on a stable group with steady meaty feeding; the species tolerates 18-30 C, so a mature, well-fed school provides the base for spawning.
Breeding Setup
Because eggs adhere to the leaves of aquatic plants (FishBase), the tank needs dense fine-leaved plants and, in practice, the roots of floating plants as spawning sites. Soft, slightly acidic water and dim, nocturnal conditions match the natural habitat.
Spawning Behavior & Trigger
The species lays 100-200 eggs that adhere to plant leaves (FishBase). Spawning is triggered by simulating the rainy season - softening and cooling the water to lower conductivity and pH while raising the level; FishBase notes that playback of a conspecific male's electric courtship display elicited spawning in ripe females, confirming the electric signal as the proximate cue.
Egg & Fry Care
Eggs are deposited among plant leaves and roots and develop there (FishBase). As a fractional spawner the female releases eggs over repeated pairings, so plant cover must be ample; captive-raised fish are reported to spawn regularly once mature under good conditions.
Common Challenges
The main difficulties are recognising a ripe pair without electrical recording and reproducing the rainy-season trigger reliably; predation of the adhesive eggs by the school itself also reduces yield, so dense planting or egg transfer helps.