One mistake many amateur aquarium owners make in their community take is combining omnivorous, herbivorous, and carnivorous fish. As most people tend to think of fish food as flakes from a bottle it's not hard to see how these kinds of mistakes can be made. Unfortunately mixing the wrong fishes can have deadly consequences for some of your pets.
Not all fish require the same diet. Like other organisms, a fish is designed with a mouth, teeth, and a digestive tract that is intended for certain types of food. It's important to keep in mind that any living creature will eat virtually anything if they are hungry enough. In other words, don't make broad assumptions about the dietary needs of a fish-based on observation alone.
Do your homework and find out what the fish needs to eat to remain healthy. There are three basic categories that fish can be classified in, based on their dietary needs. Those are carnivore, herbivore, and omnivore.
These are meat-eaters, and generally requiring live foods. They have a large mouth with sharp pointed teeth that allow them to grasp their prey and tear off large chunks of flesh, which is swallowed whole rather than ground or chewed first.
Carnivores have a short intestinal tract, and a relatively large stomach designed to hold an entire fish. Their digestive system lacks the ability to digest vegetable matter, so even though they might eat plants, they cannot derive nutrients from them as other types of fish do. Because they will chase down and eat other fish in the aquarium, carnivores are not suitable for a community tank.
On the opposite end of the dietary food chain from carnivores is the herbivore. Although herbivores can sometimes be seen eating live foods, the proper diet for an herbivore consists of plants, algae, and fruits.
They have no true stomach; instead, they possess a specialized intestine that is capable of breaking down plant matter. Their teeth are flat, which allows them to grind food before swallowing it. Because they lack a stomach for holding large volumes of food, the herbivore must eat frequently - at least several times per day. Because herbivores require frequent feedings of vegetables and fruits, they are often not the best choice for a community tank.
An omnivore will eat a variety of meat and vegetable matter. Although omnivores can and will eat vegetable matter, they cannot digest some types of grains and plants. Their teeth and digestive tract possess some of the traits of both the carnivore and the herbivore.
Omnivores are the easiest of all fish to feed, as they eat flake foods as well as live foods, and everything in between. For that reason, omnivores are an excellent choice for a community tank.
As you can see, it's important to feed your fish the proper diet, as their bodies are designed for certain types of food. If you aren't sure what type of food your fish needs, use the dietary type chart.