Is fission or fusion of antiparticles possible?
They are both as 'real' as anything particle wise. When they meet they don't 'disappear', leaving no trace of their existence. They annihilate into 'real' radiation. So you can do anything with a anti particle that you can do with a particle, as far as I know they are a sort of 'mirror symmetry', not 'negative' as in 'disappearing' into a 'nothing'.