The females look bulkere,rounder than the males and the males tend to be a little brighter / more colourful . they may be other ways i've heard it also has something to do with there black markings but not sure. If you have about 5 or six , feed them all up as I did
I fed mine well for about 10 days plenty of live mozzie lava and blood worm, then poped them all into a home made plastic mess breeding net, still fed them heaps of mozzies and next morning the bottom of the tank was covered in eggs, the tank had a sponge filter going which i turn down low. I left the adults there for another 24 hours as they could not get to there eggs then return them to there Barb tank. I placed some crushed up lettace leaves in the tank with the eggs to grown some inforsoria and left them, 4 - 5 days later i had heaps for fry sticking to the sides of the tank .....