i THink it depends on the fish cause when i had a severum with my it beat the crap out of it. My jack lives up to the name but i have heard you can put them with many fish of the same aggression, like green terrors, oscars, jaguar, meeki, and many more. when i get a larger tank i plan on putting a green terror, jag and a electric blue jack or something else instead of the electic blue jack. still trying to figure that out.
