Apparently the males blue line is bent, whereas the females is straight, I think the male also has a tiny hook like first ray on the anal fin that looks whiter than the rest of the fin.
They should be kept in groups of 5 or more at the very least as they depend on the group to feel secure. once they are used to the aquarium and get over their paranoia about being eaten, they will go their own ways but shoal again if there is a threat.
They breed a lot more than is realised in the aquarium but unless the water is very soft the eggs will become fungused or disolve.
Ken