fish don't need to eat all the time like us
they're cold blooded, therefore don't wast energy keeping their body temperature stable, like humans or dogs!
when they are shipped from asia to america, they often go 3-4-5 days without eating without light!
plus, lots of fish can eat algea and such, like livebearers or most catfish!
sure they'll be hungry, but their instinct tells them to be hungry all the time!
EDIT- very young fry need to eat everyday though, or evry second day at least to stay healthy. then again, if you have plants, they'll eat tiny bacteria that multiply in plants like java moss and such!