I heard that the "angelfish pair up for life" is a myth. Breeders often mix up the pairs to get more genetic variations of their fish. I never bred any angelfish, so I don't have a lot of experience. I do however have a pair of angelfish, which I'm relatively sure are a male and a female. I have a koi and a blue diamond, koi is the male and blue diamond is a female (at least I think so) from physical characteristics. I used to have more angelfish in the tank (4) and the koi and another platinum angelfish often fought (I assumed was for picking order?). The koi won so I thought I will have a breeding pair, but nothing ever happened. Still don't know what the reason for that is.