Most aquarium fish—including goldfish, mollies and catfish—are omnivores, eating both plant and animal matter. An omnivorous diet should consist of a staple flake food; goldfish can benefit from specially formulated goldfish flakes and pellets.
Plecos, African cichlids, pacus and silver dollars are among those who eat only plants. These fish do well with staple flake foods and algae wafers, which can be supplemented with finely chopped lettuce, spinach, zucchini, or green peas.
A few fish species primarily eat meat. These predatory pets include Jack Dempsey cichlids and bettas, who prefer to feed on frozen brine shrimp, freeze-dried tubifex worms and bloodworms. Some predatory fish, such as oscars, prefer small feeder fish.