Before i had bluejack dempseys, people told me to watch out for their agression. I keep them in with rainbows, barbs, even glass fish, and have not witnessed this aggression. I find it hard to beleive that they are related to regular jack because they are so docile. I always make sure that my bluejack male is much much larger than the regular jack female , so he does not get beat up. As far as temperment i think they are closer to communtiy fish. Infact, when i got my first bj i put him in with smaller africans..... not a good idea with these sweethearts~!
I have over 50 Male Bluejack dempseys. My 125 gal has about 21 male bluejack dempseys, ranging in size from 6-7 inches, and i have one 4.5 inch bluejack female in there with them. They get along very well together.