When your water temperature changes, the metabolism of your fish changes with it.
The amount of food that the fish require changes with the seasons.

In many natural ponds it is not necesary to feed the occupants at all as they will browse on whatever they can find. However, the cleaner and more pristine we make our ponds, the less natural foods are available, and without supplemental food, larger occupants could not survive. Tiny fish like Gambusia Mosquito Eaters never need to be fed as they can survive on the mosquito larvae in the pond. However, when we have larger fish and especially Koi that can weigh several pounds or more, feeding becomes a neccesity.

Inthe spring, as the water temperature climbs above 50F degrees, it's time to start giving your fish supplemental food. From this point until the water gets above 65F, we should only feed using vegetable based foods. Most pond foods are labeled by type and you will see labels using "Spring & Fall food" or other similar descriptions. The key here is to NOT feed the fish any HIGH PROTEIN food until the water temperature is above 65F. This is because at these lower temperatures, the fish have difficulty breaking down the proteins, while vegetable based foods are assimilated easily.

Once the water temperature is above 65F, feel free to feed ANY of the pond grade foods that are available.

Again, in the fall, when the temperatures drop, go back to feeding vegetable based food.

Most ponders do not feed at all during the winter months when the water temperature is below 50F.
The fish systems go into a semi-dormant stage and little is consumed. If you feel sorry for them and just have to give them something, then stick with limited amounts of natural fresh foods like melon, cucumber, peas, etc.
Remember, your Bio system is also in a dormant stage, so you don't want to load up your pond with debris.

Parsley is like catnip for Koi. They can't get enough of it. But, parsley is hard for the fish to eat because it is stringy and long. We have found that presenting the parsley to them on a stand allows them to browse easily.

A parsley stand can be made by inserting a foot long piece of 3/8" dowel rod into an 8" square piece of sandstone.
The dowel should be tapered at the top end to make mounting the bunch of parsley easy.
We drill a hole in the stone and glue the dowel in with epoxy. Soft stone is easier to make holes in and you could always pour a base around a dowel using concrete.

Once constructed, buy a head of parsley and remove any wire bindings. Then place a couple of fat rubber bands around the base of the parsley and slide the whole thing down over the dowel rod. When you drop this into the pond, it looks like a natural bush and the Koi will devour it readily.

The fish will rip off small chunks of the greens and keep coming back for more. It's fun to watch our large Koi lined up all around the stand, and taking turns at nipping off the leaves. Our fish will completely devour a head of Parsley in about 30 minutes, reducing it to a few stems hidden by the rubber bands.