Here's a very interesting article on this topic:
The 24 authors who collaborated on this paper obviously belong to the "splitter" school of biological thought, whose adherents seem to think that every subspecies, color morph, geographical variation or other slightly different version of any given species is actually a unique and distinct species in its own right. Unlike many splitters, however, these folks make a strong and convincing case for the 3-species idea.
Bearing in mind that this paper is only about three years old, it's possible that numerous keepers have kept one or both of these new species, but bought them and referred to them all as E.electricus because that was the only accepted species prior to this work. It's not as if a guy in a canoe, wearing a pith helmet and carrying a bull whip, penetrated some remote Amazonian backwater and found the first specimen of E.voltai or E.varii. "New" species like this are "discovered" in labs or museum collections, sometimes by examining and comparing type material collected and preserved years earlier. Some of the characteristics the authors described here were based on very small sampling sizes...in some cases, just one single specimen.
The sum total of my experience consists of a single solitary E.electricus (by default). I can't begin to guess about aggressiveness as it was always alone, and have no idea about breeding or sexual dimorphism. Hopefully if you ever find more info you will update this thread?
