I heard a male and female would not fight but I have tried many times whenever my lfs would bring a new one in without luck. Best bet is to use an accumulation box and see if they show aggression
I tried it once. They beat each other up so bad, I had to pull one of the two and put it back in QT and then returned it to the LFS. Unfortunately I have read they're like clown fish in that one will change gender and submit to the Other. It's an expensive exercise though if they just kill one or end up kill each other. . . If Diver's den or somewhere ever has a mated pair for sale, I'm definitely on it though. Then again, my luck they'd forget about each other in shipping and kill each other in my tank in a quarrel.