Instructions
Research your fish to see whether it's an herbivore, carnivore or omnivore (if you don't know already). Provide dry or wet algae for an herbivore, frozen seafood (such as brine, krill, shrimp or small fish) for your herbivore and a combination for your omnivore. If you're feeding your fish seafood, chop it into small pieces before giving it to your fish.
Buy some food from the fish store that corresponds to your type of fish. For instance, if you have an herbivore marine pet, look for flakes or pellets that are made for herbivore saltwater fish. The premade foods should be labeled according to the type of fish and food. If you are confused, ask a store attendant for help.
Put a moderate amount of food in the tank and observe how much your fish eats. A general rule of thumb is that you should feed the fish no more than it can consume in 5 minutes. If you find that the fish is eating your pinch of food in less than 5 minutes, considering giving it more food. Conversely, if you see that there is a lot of food left over after 5 minutes, feed it less.
Feed your fish a small amount of food several times a day, at different times throughout the day. If you can't manage to feed your fish several small meals throughout the day, feed it two medium-size meals: one early in the day, and one at night.
How to Feed Marine Fish
Marine fish differ from many other common pet fish because they live in saltwater. Most of the time, marine fish are caught in the wild, as opposed to freshwater fish, which are often raised in tanks or ponds. Because of this, the dietary requirements of marine fish are slightly different than those of common freshwater fish. It's important to mimic the habitat of a marine fish as closely as possible, both in their environment and in their feeding habits.