Instructions
Look at the fish's papilla (or breeding tube). This is a small pink organ on the underside of the fish between the ventral fin and the anal fin. After spawning, the female angelfish will have a larger papilla. It will be more blunt than it is on a male, and when she is carrying eggs, there will a large bulge around it.
Look at your fish's behavior. Male angelfish are more territorial than females. When a female is carrying eggs, the males in the tank will form a papilla. If you have other angelfish in the tank that do not form a papilla when a female is carrying eggs, they are female, or possibly unhealthy males.
Look at the fish's anal fin. Some sources claim if the angle of this fin is around 100 to 110 degrees, it is female, and an angle around 120 to 150 degrees indicates a male. This method may not work with all varieties of angelfish.
How to Tell the Difference Between Male & Female Angelfish
Determining the sex of an angelfish can be challenging for the inexperienced. Many times, immature angelfish are the most difficult to sex because they seem to have no physical differences until they are ready to mate. During breeding season, however, some differences are more noticeable. Knowing what these differences are, and how and where to look for them, will save you a lot of frustration when trying to determine the sex of your angelfish.