I am convinced if you put a pair of convicts in water in a leather boot they would breed and most of their fry would live. The female convict I used to have would attack any of her tankmates when she was guarding eggs. She never got bigger than 3" but consistently pushed around a green terror and an oscar. She was so tough she pulled part of her males lower jaw off during a breeding cycle.
I had to separate them. I tried using fry for feeders, but some of them always survived. If you have a breeding pair of convicts, be prepared to ask yourself the title question of this topic time and time again. If you are lucky you could find a LFS that will take them off of your hands.