The Paradise fish might fight a Betta to the finish. They can be very aggressive, with the males more colorful, and a little worse for attacking other fish than the female. Two male Paradise fish will try to kill each other like a Betta. As long as you give them room they don`t seem too bad, but the one I have now killed one particular Tiger Barb. Now that the Barb is gone it just threatens the others a little and never attacks. It seems to pick and choose which fish it dosen`t like.