Candling: Candling is the process of holding the egg up to a light source to see if it contains a developing embryo. If the egg is fertile, you will see a small dark spot, which is the embryo, floating in the center of the egg. If the egg is infertile, you will not see any dark spots.
Floating test: The floating test is another way to tell if an egg is fertile. Place the egg in a bowl of water and let it sit for birkaç minutes. If the egg sinks, it is likely to be fertile. If the egg floats, it is likely to be infertile.
Age of the egg: Duck eggs can be hatched for up to 28 days after they are laid. However, the chances of hatching decrease the older the egg gets. The best chance of hatching is within the first 10 days of laying.
If you are not sure whether or not a duck egg is fertile, you can always try to hatch it. If the egg is fertile, it will hatch within 28 days. If the egg is infertile, it will not hatch.