Sexing angelfish or "Pterophyllum scalare" can be very difficult. Many breeders just wait until two angelfish pair up and then move the pair to another tank. Then if they get viable spawn you know you have a male / female pair! Now if you want to play match maker you need to know who is male and who is female.
Tip 1: The Bump
Not all strains of angelfish will have the bump and many breeders try to breed this trait out. I like it but I don't breed for or against it. This pre dorsal hump, it sorta looks like a cave mans fore head, will become more pronounced on a male and give you an easy who's who. Unfortunately these bumps don't start to develop until they are close a year old.
Tip 2: The Papilla
When one of your females decides she wants to breed she will drop her breeding tube or papilla and all the males in the tank will follow suit. The angelfish papilla is located between the anal fin and the ventral fin.
The female papilla is relatively larger then the male and blunted.
The male papilla is smaller and thinner.
Tip 3: Even the best breeders can't sex an angelfish 100% of the time. Let them pair up naturally and once you have a proven pair then you can start mixing and matching!