fish · Sternopygidae
Glass knifefish
Eigenmannia virescens
Wild range: East of the Andes from the Orinoco south to the Río de la Plata / lower Paraná system; Magdelena and Amazon drainages also cited. Type/typical southern E. virescens is associated with La Plata–Paraná; aquarium imports are often other Eigenmannia (see natural_range_notes). (South America)
.jpg){kind=link}
At a glance: Glass knifefish care
Compiled reference information. Review the care notes and original sources below.
What temperature is listed for Glass knifefish?
The compiled profile lists 23.0–28.0 °C for Glass knifefish (Eigenmannia virescens). Check the original sources below for context and differing recommendations.
What tank size is listed for Glass knifefish?
The profile lists a minimum tank volume of 100.0 US gallons (379.0 liters). Volume alone does not establish suitability; consider dimensions, group size and other inhabitants alongside the full care notes.
What pH is listed for Glass knifefish?
The compiled profile lists a pH of 6.0–7.0. Review the cited care sources alongside the other water parameters in this profile.
Natural habitat
A long, laterally compressed, semi-transparent South American glass knifefish (Sternopygidae) that swims by undulating a continuous anal fin and can reverse direction without turning. It is weakly electric (neurogenic EOD) and uses electrolocation for navigation, hunting, and social communication. Adults are strongly size-dimorphic (males much larger than females). By day it hides in tubes, wood, or dense cover under dim light; at night it forages for insect larvae and small prey through the midwater.
Where they are found
Catalog primary locked as Eigenmannia virescens (Valenciennes, 1836): FishBase SpecCode 12221, GBIF, NCBI, and Eschmeyer’s Catalog of Fishes treat the name as available from the 1836 plate (basionym Sternachus virescens). ITIS TSN 163333 still lists (Valenciennes, 1842) for the same valid taxon — year discrepancy noted, CoF/FishBase 1836 preferred. Synonyms recorded in aliases: Sternachus virescens, Eigenmannia lineata, Sternopygus lineatus, Sternopygus tumifrons (Maidenhead; AquaInfo; Atlarium/FishBase synonymy). Common trade alias Green knifefish. LOOKALIKE / SPECIES-COMPLEX CAUTION (not a deferral): aquarium 'glass knifefish' / 'E. virescens' shipments are frequently other Eigenmannia, especially members of the E. trilineata species-group, E. sp. aff. trilineata 'Orinoco', E. limbata, and undescribed forms; Aquarium Glaser notes true southern E. virescens (La Plata / lower Paraná) is seldom imported and that wholesalers often keep labelling fish as E. virescens because exact ID is rarely possible and husbandry is similar across the genus (Peixoto et al. trilineata-group revisions; Aquarium Glaser 2024). Catalog row remains E. virescens as the established trade/ITIS name; treat lookalikes as a caution, not a reason to defer. Distinct from black-ghost-knifefish (Apteronotus albifrons, Apteronotidae) and african-knifefish (Xenomystus nigri). Family Sternopygidae; order Gymnotiformes. IUCN Least Concern (assessed 2020-12-02; FishBase 2025-2).
Aquarium care
Plan a long-footprint tank of at least 100 US gallons (~379 L) for adults: LiveAquaria lists 100 gal; Atlarium ≥300 L with a 120–150 cm footprint; Fast Aquatics 75 gal; Maidenhead requires at least ~6 ft long × 2.5 ft wide because knifefish cannot bend around short tanks (especially large males). Temperature locked 23–28°C (Maidenhead 23–28; LiveAquaria 73–82°F ≈ 23–28; Fast Aquatics 74–80°F; Atlarium 22–28; FishBase wild subtropical band 20–30°C noted but not adopted as the aquarium lock). pH 6.0–7.0 and GH 2–15 dGH (FishBase pH 6.0–7.0 / dH 2–15; Maidenhead pH 6.0–7.0 / dH ≤15; LiveAquaria pH 6.0–7.0; AquaInfo pH 6.0–7.0 / GH 2–15). Soft sand (protect the long anal fin), dim lighting or floating plants, and multiple dark retreats (PVC tubes, wood tangles, caves). Gentle flow with efficient filtration — they prefer still/slow water (FishBase; AquaInfo; Maidenhead) and are sensitive to nitrate and sudden chemistry swings. Scaleless: use half-dose or manufacturer-safe medications and avoid copper. Intermediate difficulty; specialist oddball rather than a beginner community fish.
Feeding
Nocturnal micro-predator / carnivore of insect larvae and small fish (FishBase; Maidenhead; AquaInfo). Offer frozen and live bloodworm, mosquito larvae, mysis, brine shrimp, tubifex/blackworm, and chopped earthworm; many learn sinking carnivore pellets over time; flakes alone are usually inadequate (Maidenhead; LiveAquaria; AquaInfo; Fast Aquatics). Feed after lights-out so daytime fish do not outcompete them. Will eat nano tankmates and shrimp once large.
Compatibility
Peaceful specialist community fish with similar-sized, calm tankmates; gregarious — keep a group of about 5–6+ in a large tank (Maidenhead ≥6; LiveAquaria social; Atlarium solitary or ≥5, avoid pairs). Do not mix with other weakly electric knifefish if space is limited. Avoid boisterous species and anything small enough to eat (including shrimp and snails) (Maidenhead; AquaInfo). communitysafe is false because of predation on typical nano community fish. nanook false.
Breeding
Difficult in home aquaria. Simulate rainy season with cooler soft water (AquaInfo cites dH 2–4), conductivity drop, and live food. Spawning often early morning; adhesive eggs (≈100–200 per bout) among floating-plant roots; remove eggs or parents; fry on Artemia nauplii (Maidenhead; AquaInfo; FishBase; Aquarium Glaser). Males grow much larger than females (Maidenhead; FishBase; AquaInfo).
Sources
Compiled from multiple independent care sheets — not copied from a single site.