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Others / Knifefish / Glass Knife Fish

Glass Knife Fish, Green Knife Fish
Eigenmannia virescens

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Synonyms: Cryptops humboldtii, C. lienatus, C. virescens, Eigenmannia lineata, E. humboldtii, Sternarchus virescens, Sternopygus humboldtii, S. lineatus
Physical description: An elongated fish that lacks a caudal fin. The body is transparent but light brown colored. Sometimes the flanks may have a green iridescence. The backbone can be seen through the body. Two fine, lateral stripes are present; on that runs along the base of the transparent anal fin, and the other located just above this stripe. The head is dark brown to pinkish beige.
Size/Length: Males to 18" (46 cm), females rarely exceed 11" (28 cm)
Similar species: Other Eigenmannia species
S: bottom, middle
Habitat: South America; underneath islands of floating meadows in floodplains in the Amazon basin
Aquarium: A tank measuring 48" (122 cm) with a capacity of 55 gallons (209 L) is recommended. Plant the tank heavily and use a cover of floating plants to diffuse the lighting. Provide plenty of hiding places among rocks, wood, and pipes. This species prefers "old water."
Water chemistry: pH 6-7.5 (6.9); 4-15 dH (10); 73-82°F (23-28°C)
Social behavior: A peaceful Knifefish that, unusually, should be kept in groups. A social structure will be formed with a dominant fish and weaker members. Combine with peaceful species too large to swallow.
Suggested companions: Loricarids, Armored Catfish, Doradids, larger tetras, dwarf Acaras, Angelfish, Headstanders
FOOD: Live; small fish, snails, crustaceans, earthworms, mosquito larvae, Tubifex ; tablets, acclimated individuals may accept flakes.
Sexual differences: Males are obviously larger and have a larger caudal penuncle.
Breeding techniques: Stimulating the rainy season helps initiate spawning. Use soft water (2-4 dH). Spawning takes place in the early morning hours. Eggs are laid in small amounts during each pairing, which lasts from 3-6 hours. In all, 100-200 eggs are usually laid on roots of floating plants. Remove eggs and transfer them to rearing tank. Raise the fry on Artemia nauplii.
Breeding potential: 9. Breeding is very difficult.
Remarks: During spawning, the Glass Knife Fish emits electrical signals. These electrical signals can be heard with the aid of an amplifier, a speaker, and two electrodes. These signals produce songs that are thought to help fish to pair up. Use a good water conditioner. Sensitive to new water added during water changes. Prefer water that has been standing for a while.
Difficulty of care: 6. This nocturnal species requires a diet of live foods and is sensitive to changing water conditions.


By Rhett Butler   Mongabay.com