At the end, Gombei threw out all of his duck catchers and decided to do them a favor, so he grew a farm so they could get food from there and live happily ever after.
In the story "Gombei and the Wild Ducks", Gombei was always told that catching more than a duck a day was cruel so he followed that rule. But one day, he wanted more ducks so he decided to catch 100 in one day and when he was about to, he suddenly turned to a duck.
The theme of the story is to treat people the way you want to be treated
When that happened, he got captured by someone just like he would capture the poor ducks. After that he learned his lesson and felt bad for trying to catch 100 ducks in the morning and knew he should never do it again. Then he suddenly turned back to a human!