Angelfish (Pterophyllum scalare) are very common pet fish. They are tropical freshwater aquarium fish. Because of the high demand for them, angelfish are available in nearly every pet shop. It is not easy to distinguish between male and female angelfish but observing their behaviour, noting their shape and size and watching them while breeding can help you determine which of your angelfish are females and which are males.
Watch your angelfish as they mate. As there are no visible differences between males and females, the only way to distinguish the fish's sex is during spawning. The female lays the eggs and the male fertilises them. A male angelfish has a cone-shaped breeding tube or papilla. This is a small pink protrusion between the ventral and anal fins. A female has a round teardrop-shaped papilla. The female papilla is larger and more blunt than a male's.
Pay attention to your angelfish's behaviour. Males are more territorial and will show their papilla around a female. They will also eat eggs that were fertilised by another male.
Examine the angelfish's build. Males have a rounded crown, grow faster and have a thicker body. Females have a straighter line from their dorsal to their eyes. The male angelfish will have a larger angle from the forward edge of the belly and the anal fin than a female, between 120 and 150 degrees. These differences are only visible with mature angelfish.