The red-bellied Pacu (Colossoma macropomum) is a peaceful aquarium fish that is often mistaken for its aggressive cousin the piranha. Although these two fish look similar, looks are all they have in common as the Pacu have a quiet nature and are vegetarians, while piranha are dangerous aggressive carnivores. Make sure when selecting your fish that you are taking home a Pacu and not a pirhana!

Appearance and Behavior

The Pacu seen most commonly in aquarium stores is the red-bellied species. These fish can grow to be quite large, up to 2 feet if given the room, so start with a small juvenile, as they will grow very fast. The younger fish have a tendency to be more aggressive with tank mates but mellow as they get a little older. Males can be distinguished from females by the more intense red color to the belly. They breed poorly in a home aquarium.

Feeding and Tank requirements

Pacus are vegetarians and will accept flakes, lettuce, spinach, even chopped zucchini. Live plants kept in the tank will usually suffer damage or will be completely eaten. These fish need a roomy tank as they do not thrive well in cramped quarters. Maintain water temperature between 72 to 82 degrees Fahrenheit, pH 5.0 to 8.0. Most Pacu outgrow their tanks.

Special Concerns

Some hobbyists report that Pacu are more sensitive to nitrogen waste products than other fish from their geographical region. More frequent water changes or additional filtration will be required to keep the levels low. Acceptable tank mates to try are rosy Tetra, black banded Leporinus, severum, butterfly fish and rasbora.