It all depends, if they are in a pond or a tank ?
And, if they are in a pond, just how long is the pond established?
The reason why I am asking all of those questions is the fact, that there are different choices, and different circumstances.....All, which are simple, and very easy to remedy, I might add.
If the fish are in the tank, they have feeding tablets which are slow release up to 14 days. (Read the instructions, because the dosage all depends on how many fish you have!)
If the fish happen to be in an established pond, meaning with some algea growths, larvae etc, you can leave without feeling bad, because they will forage for food.
If no natural food source is present, some slow release feeding tablets are also available for pond use.
(Some tablets are different, since the ph level might be different in pond vs. tank, influencing the disolving of the tablets!)
Best to go or call or go to your fish place/ aquatic store in town, and get some "hands on" info.
That way your fish will be happy campers while you are gone, and you have peace of mind
Good luck!