'Blue rams' can be sexed using a variety of characteristics. The males
are generally larger (most prominent in adults), have slightly longer
fins (dorsal) and lack the blue spangles in the black mid-lateral spot
found in the females. Wild fish are very easy to distingush, but the
cultured varieties may be a little harder, assuming both sexes are
present. If I were asked for one reliable difference, I would say the
blue spangles within the black mid-lateral blotch is the best method (it
also works on young fish and the cultured varieties).