Walleye can weigh about 25% more in the spring just before spawn because they are full of eggs and body fat. After spawn the drop all their eggs so they weigh much less, but they do still have body fat so they can be heavier depending on weather they feed or how much time has passed since spawn.
By Fall the eggs start growing again in females, and of course they weigh more. As it gets colder, the egg sacs get bigger and they start putting on body fat. So a 28″ Walleye could weigh anywhere from 7 pounds up to 10 pounds. Thats why so many fisherman go by inches when it comes to Walleye, they get robbed if the same fish loses 5 pounds in the spring and summer.