Sorry, he was just adopted. My Jack Dempsey wasn't aggressive at all but he was very defensive. My Oscar liked to try and take over whatever rock the dempsey claimed, and I knew it was going to be a matter of time when the Dempsey was going to have enough. He cornered the Dempsey in a cave and the dempsey took a chunk out of him, he is healing up great, almost back to 100% but that was enough for me to separate them. (The Oscar we have had twice as long and he was picked out by my wife, thats why we chose the demspey to go).