There are numerous fish foods available which makes it difficult to know which food is right for your fish. Fish have different diets based on their species so it's important to know what category your fish is in:
Herbivore - plant eater
Carnivore - meat eater
Omnivore - consumer of both plants and
meaty foods... the vast majority of aquarium
fish fit into this category
"Many of the staple diets do a very good job of providing a broad range of essential nutrients required for good health. But, we believe that variety in the diet is important to good nutrition and the well-being of your fish. Offering a variety of foods, in addition to the "staple" diet, ensures better nutrition and enriches the diet of your fish with more tastes and textures." - LiveAquaria.com
Click the image below to see use this chart as a guideline for feeding your freshwater or saltwater fish.