I have gold fish in an outdoor pond. During the winter months I feed them a regular amount and they are doing well. As we are coming into summer there are more insects around, that fall into the pond, and mosquitoes, which lay larvae in the fishpond, which the fish eat.
I don't want to over feed my fish. How do I know how much to feed them when the natural environment starts to provide them with food?
The only estimate I keep hearing on this topic is to feed fish as much as they can eat in about five minutes. As long as the fish eat nearly everything of the food it wasn't too much. I suggest to use floating food. It makes it far easier to keep track if everything is eaten and you train your fish to search for food on the top of the pond so they are visible more often.
It is hard to estimate the amount of insects that are eaten by your fish. I simply would adjust the amount by above guideline. The biggest problem with overfeeding seems to be massive growth of algae, at least I have never heard of problems with obese goldfish.