I keep the Eingemannia in the 576-litres tank. Personally I'm interesting to Ramphictys species-can I keep they? Are they peaceful toward other fishes (e.g. Gymnothorax and Polypterus)?
Yeah, they're very mellow...if you can find them lol. The Gymnotus species are probably the meanest of the American knives (well, except for the electric eel)