Depends on the fish.
I feed my rainbow trout standard trout pellets but also crickets, minnows, snails, worms, shrimp, bug nymphs, ect.
My gar get carnivorous pellets but also feeder fish, nightcrawlers, grasshoppers and pieces of meat. Same with my sunfish.
My other fish get a variety of flake foods, pellets, vegetables and meats.