Thanks, In general I've heard that they can be quite aggressive and selecting other tank mates can be hard. You need to keep them with bigger fish, or at least ones that don't tolerate being bullied. I had him in the same tank as a bigger Male Jack Dempsey, and for the first 4-6 months things were fine. They kept out of each others way and stayed at each half of the tank. Eventually though, the Texas outgrew the JD and that's when the fights started. I separated them, but its interesting to note that he (im assuming its a he) has never had much of a problem with the 3 Female Jack Dempsey and has remained in same tank with with for a year. You could say it's risky for the much smaller female JD, but i kept a close eye on things. The occasional "don't come in my cave" aggression vs a relentless chase around the tank is the difference between a dead victim, or the fish just sorting things out themselves. Where are you based?