How do you tell the sex of a jack dempsey?
Most times the male fish is much more aggressive than the female.
It is hard to tell by color because they don't vary much, but their fins (dorsal and anal), the male has pointy fins and the female in most cases does not.
if you are thinking of reproducing jack dempseys be careful to have the right size of tank you need :]
hope this helps a bit! :D