i bred jags for some time and I noticed the same thing. Although eating the eggs is actually what there supposed to do. I would see a lot of eggs layed and then as the days would go on, there would be half the eggs there. What happens is some die due to many different reasons. Not enough sperm, poor water quality, lack of oxygen coming to eggs etc. So always some will die off. As they die off the parents will pick them off and usually eat a few good ones by accident but thats what they need to do to make sure that the majority survive. Although if they are eating all of them, then that means for some reason there all not doing well. I remember mine ate the first couple batches and then the third batch they raised.
Some suggestions
1.) Try to improve water quality. I don't know how your water is but check your temp. Temp needs to be a bit higher for the eggs but not to high because the higher the temp the less oxygen in water. I bred my jags at 80. Make sure water quality is perfect. I don't mean like 20-30 ppm nitrate I mean like 10 or less. The less the better.
2.) Do small water changes like every day or second day for now so that way the water is always good. Because once the eggs hatch you should not do any water changes for about a week. Any changes to water would cause the eggs or fry to die.
3.) How big is the tank?????
4.) is there any other fish in the tank because maybe they are not eating the eggs someone else is. Plecos and other bottom feeders love to sneek up at night and scarf down some eggs.
