Fish can go up to 14 days without eating according to Google (lol I'm not gonna pretend like I'm a marine biologist or something for the forums)
But 6 days is pushing it because you should feed at least every other day for healthy normal growing fish/and or other species.
My advice is to have someone come in every other day to come and put a pinch of food in. I know a lot of people are nervous about letting people who know nothing about fish, handle fish. But if it makes you feel better, do anything you can to make the job easier for the person coming in and give them simple but specific instructions. Sticky notes on the tank or stand is a good idea.
You could go to your local drug store and pick up a pill bottle schedule thingy. A week worth and put a pinch of food for the days they will come in, this way they know exactly how much and make sure to include on a sticky note that they shouldn't feed any more! Even if the fish looks hungry still, some people are too quick to fall for that. Lol
I'll lay it out for you to make it simple for you and whoever takes care of your fish in the near future.
S- the day you leave/feed normally
M- no food
T- feed a pinch
W- no food
T- feed a pinch
F- no food
S- feed a pinch
Understand? Good luck man and don't worry about them too much. They'll be fine. Make sure to water change and make sure all equipment is doing good and will last at least until you get back.