Rainbow fish are omnivores that eat a variety of foods in the wild, including aquatic and terrestrial insects, insect larvae, crustaceans, phytoplankton, zooplankton and detritus. A suitable diet for the aquarium includes algae, vegetables, frozen and live mosquito larvae, Daphnia and bloodworm.
Rainbow fish are native to numerous parts of the Southern Hemisphere, and although habitat conditions vary a great deal from species to species, these fish accept almost any food in captivity. A varied diet promotes general health, while the inclusion of live and frozen foods improves coloring. High-quality flake food for omnivores and herbivores provides a suitable base food, and the natural algae growing in a fish tank provides nutrients while allowing the fish to forage as they would in the wild. Rainbow fish also appreciate vegetables, such as boiled peas, zucchini and pumpkin.
Meaty foods should constitute 35 to 40 percent of the rainbow fish's diet. Suitable meat supplements include brine shrimp and other common freshwater fish foods, chopped earthworms and fish fillets. Live foods allow the fish to engage in its characteristic predatory behavior. Rainbow fish are surface dwellers and prefer floating foods. Because they are greedy eaters that are easy to overfeed, it is important to feed them several small meals a day and no more than they can eat in 3 to 5 minutes.