being very well conditioned can help, but sometimes the little buggers eat them anyways, I had one that just did the same thing and he was conditioned for over a month.
Constantine and Modaz gave me good advice on what do do with the egg eaters. One way was to steal the nest after they are done spawning and raise the babies in very shallow water and the other was to feed the daddy very small amounts of pellets during the care of the fry- not enough to pollout the water, but enough to take the edge off his hunger.
there was a thread by me somewere still on the first page that both went into greater detail with.
sorry he ate the eggs, sometimes they will do so when stressed, hungery, or for seemly no reason at all.