Candling duck egg- What is normal

[2Myanimals]

I dont know exactly how many weeks my duck has been sitting on her eggs since her sister joined her a few days later and they seem to swap eggs!! I candled them the other day and could see a solid mass with air cell at the round tip. When I tilted the egg, I could see some fluid at the top moving. Does that mean the eggs are not good? HELP.

 

[ducksinarow]

Look up duck egg diary on this in the search bar. Someone posted some pictures of eggs. The egg might just be full of duckling. I would let mama duck throw out which eggs are bad. I also have 2 sitting ducks. I am just allowing them to make the choice of which eggs to toss.