How do you sex a Discus fish? I am curious because I want to try and get a pair to breed in a tank I have made the water specially for Discus fish. But I want to sex my current Discus to tell if it's a male or female.
It's very difficult to tell with discus. The female is the one laying the eggs. I know that sounds tongue-in-cheek, but I've had pairs that formed and I had no idea which was which until they spawned. This is sometimes complicated by the fact that two females will attempt to spawn and both are laying eggs.
Mark is right on - you will not likely be able to sex discus until after they pair up and have actually spawned - and even then you may find you have 2 females, with an unfertilized spawn of eggs.