I have a mature (8") Jack Dempsey in a 55 gallon aquarium. I introduced two juveniles (2-3") last year in the hopes of one of them becoming a mate. It worked. One of the females grew alarmingly fast, she equaled the mature Dempsey in size in the course of about six months. The other juvenile Dempsey only grew about an inch in two months or so, and he went back to the LFS after it became apparent that I had a male and female.
I guess some fish just need a little motivation to grow.
P.S. - The Dempsey's have spawned about 4-5 times in the last six months or so.
