Did you read the link aquaparadise provided at all? I glanced at it for a couple seconds and read this: "Electric fishes just don’t like other electric fishes. Elephant noses dislike other nosers and most of the knife fishes."
And that may be true for the most part but I have an elephant nose and a black ghost knife who are the best of freinds. In a 410 gallon aquarium I frequently find them right next to each other. Whether they are feeding or just "hangin" they get along just fine, and have for over a year. Go figure. Oh, and the ghost is twice the length of the elephant nose and at least 5 times his weight.
