- males lack blue "spangling" throughout their black spot (can be completely black in the middle with spangling around). Females will have blue "spangling" through the spot. (least conclusive)
- in non-longfin variants, the dorsal and anal fin of females barely reach base of caudal (tail) fin. (most accurate)
- females have a red/pink belly when they are in the mood to spawn.
lots of information and ways of sexing by searching "sexing blue ram" or "sexing mikrogeophagus ramirezi" on the web
Another thing to consider: many rams are hormone injected to brighten their colors. Ask your LFS if their supplier does this. If they dont know you can usually tell because the fish have brilliant coloration despite being stressed by the LFS tanks. I purchased 3 rams from a very well kept LFS that were hormone injected and all 3 were dead within a month despite perfect water conditions. I purchased two from a breeder and they are alive and healthy to this day.
Also if you are looking for a pair, try and see which ones in the LFS are paired off. Just buying a male and female will not mean they pair off.
Looks like a male and female to me. Evertime I have put a male and female together they have almost always paired. Looks like you have them in a community tank. If so, unless you plan to remove the eggs there isn't much of a chance of ending up with fry.