Angelic fish?

I've got an extremely handsome and fertile pair of angel fish in our tropical fishtank. They lay eggs every 3-4 weeks over the summer - well the female does anyway.
Sadly within 24 hours the eggs disappear and last year I spent ages removing different fish from the tank only to find that the putative parents were in fact the ones supplementing their diet with additional protein! Ah well, that's nature in the raw I'm afraid!