While the specific diet of a freshwater fish depends on its species, most eat smaller fish, leeches, worms, insects, crustaceans, plankton and krill. When kept in an aquarium, freshwater fish can thrive on a combination of fortified flake food, pellets, sticks and wafers.
Food for aquarium freshwater fish is divided into three categories: dry, freeze-dried and frozen. Of the three, freeze-dried is the most convenient, preserving the food's original palatability and nutrition, while frozen is the healthiest, using higher quality organisms. Flake food is not suggested for freshwater fish longer than 4 inches as they are unable to eat enough to remain healthy at that size.
When raising freshwater fish in an aquarium, adding micro foods for the smallest fish is helpful. Egg yolks, algae-loaded water and infusoria should all be added to the tank. Infusoria can be created by placing a banana in a jar of aquarium water and slowly adding the cloudy water to the tank.
Freshwater fish can be divided into four categories: herbivores, omnivores, carnivores and limnivores. Carnivorous freshwater fish tend to eat less frequently than the others, while limnivores are constantly feeding on algae and detritus. Some species of fish eat mollusks, while larger carnivores enjoy house flies. Larger freshwater fish can even eat frogs and goldfish.