Looked at their anal fins, female smaller and rounder, male wider and not so transparent. When males are ready to breed they flex their anal fin like a cup. During spawning the male and female flutter their bodies side to side while the female releases the eggs, the male catches what he cans in his cupped anal fin fertilize's them and scatter's the eggs on plants,spawing mop or substrate. When I realized mine were breeding I made a spawing mop with forest green colored yarn purchased from a hobby shop. Make sure you boil colored yarns, because color may bleed.