you will need a large tank there was a LFS that kept one in a 1000 gal. tank with 2 pacus & an arow. I'm not personaly into them though. All knifefish will use shock to defend themselves or if they get pissed to be offensive as well as kill food. if the fish feels no need to defend itself or to take territory it will probaly be ok with enough space. People are the only creatures that kill senselessly.