Red Belly Pacu (Piaractus Brachypomus): Ultimate Care Guide

Native to calm South American waters, Red Belly Pacu can be a challenging fish for beginning hobbyists due to its large tank requirements and heavy filtration needs. This fish can resemble the Red Belly Piranha with a silver body and a reddish-orange belly. Unlike Piranhas, Pacus are vegetarian and have squarish teeth that resemble those of humans.

If you are up for the challenge of raising a Red Belly Pacu, there are some things you’ll need to know first. Let’s look at some details about this large yet docile fish.

Red Belly Pacu (Piaractus Brachypomus)
Red Belly Pacu (Piaractus Brachypomus). Edited. Wisky, CC BY-SA 3.0

Are Red Belly Pacu a Piranha?

Although Red Belly Pacu outwardly resembles the Red Belly Piranha, it is a different species. Piranhas are carnivores and have sharp pointed teeth. The Pacu is a herbivore and has squarish teeth that resemble those of humans.

Are Red Belly Pacu Aggressive?

Red Belly Pacu are usually docile fish. They may nip at smaller fish, and a small “nip” can be serious due to their large size. This species is mostly peaceful and won’t cause trouble with most other tank mates.

Do Red Belly Pacu have teeth?

Red Belly Pacu have squared-off teeth, ideal for eating vegetation. These teeth can resemble those of humans.

Red Belly Pacu Care

Red Belly Pacus need very large tanks and heavy water filtration. This fish species has special care needs. You’ll need to know some details before attempting to raise one or more. This article will cover most of what is needed when caring for a Red Belly Pacu.


Red Belly Pacu prefers water temperatures between 75° and 80° F.

Water pH

Red Belly Pacu needs water with a neutral pH between 6.5 and 7.5.

Red Belly Pacu Size

Red Belly Pacu can easily reach over 12 inches in length. In some cases, they can grow to 24 inches. This large final size can surprise new owners who often don’t have tanks large enough for this species. Plan for an aquarium of at least 250 gallons, preferably larger.

Growth Rate

Red Belly Pacu can grow extremely fast, sometimes reaching 12 inches in under a year!

Max Size in the Wild

In the wild, Red Belly Pacu can reach up to 30 inches.

Average Size in Aquarium

In most home aquariums, Red Belly Pacu will reach around 14 inches. Though they can grow to 24 inches and will need enough tank space to support this large final size.

Food & Diet

Red Belly Pacu are herbivores and eat large quantities of aquatic plants along with any fruits and nuts they can find. In an aquarium, they can be fed herbivore pellets, but this diet should be varied to include foods like grapes, broccoli, peas, and even bananas!

While their diet should mainly include raw vegetables and vegetable-based prepared foods, they also appreciate the occasional snack of crickets or other small insects. In the wild, Red Belly Pacu has varied diets that include small quantities of fish and insects.


Red Belly Pacu usually lives 5 to 15 years but can live even longer with the right care.

Tank Size

Red Belly Pacu are large fish with big tank size requirements. You’ll need at least a 250-gallon aquarium to provide enough room for this enormous species. You’ll need an even larger tank if you keep more than one Pacu.

Tank Setup

Red Belly Pacu needs large tanks with substrates that support neutral water pH. Avoid plants, as this large herbivore will eat the most common aquarium plants. The tank size will be the most critical choice you can make. 250 gallons or more is recommended. Few hobbyists have the large tanks this species needs. Red Belly Pacu is often seen in large public aquariums for this reason.

Avoid substrates that contain crushed coral or aragonite sand, as these can raise water alkalinity. You should also avoid aquarium soils that buffer acidity, which can send your water chemistry too far into the acidic range. Red Belly Pacus prefer water as close to neutral as possible. The best substrate choices are inert media such as sand or gravel.

Ensure your tank is equipped with a strong cover. Red Belly Pacus will jump, and their large size means they can break any tank cover that isn’t sturdy.

Water quality is going to be a big challenge with this species. Red Belly Pacu is a large and messy fish that needs frequent water changes and powerful filtration. This is usually achieved with canister filters. You’ll want a filter capacity that can turn the entire contents of your tank 4 to 5 times an hour. If you have a 250-gallon tank, you’ll need a filter system capable of running at 1000 to 1250 gallons per hour!

If you are committed to keeping large freshwater fish such as the Red Belly Pacu, consider installing a sump filter. Sump filters are common in marine aquariums but can be useful for large freshwater tanks. The recommended size for a sump filter is 20% of the water volume of your main tank, but the larger, the better. Sump filters are more efficient than canister filters as they can hold more filter media.

You can also light your sump and use it to grow aquatic plants. Growing aquatic plants will increase water quality and reduce the need for water changes. Large herbivores like Red Belly Pacu will eat most plants they can reach. A planted sump is a great way to have the benefits of a planted tank without exposing the plants to fish that might eat them.


Red Belly Pacu need lots of space to spawn. This is unlikely to happen in an aquarium and usually requires large ponds. This species breeds by scattering eggs. The female casts eggs into the water, and the male will follow and fertilize. A female will lay up to 400,000 eggs! A problem when breeding this species is the fact they eagerly eat eggs as soon as they’re laid.

Red Belly Pacu are bred for food in South America and parts of Asia. These breeders use large hatchery ponds and induce breeding with pituitary extract. Unless you plan on breeding this species commercially, this complication and expense are probably not worth it.

Red Belly Pacu Male or Female

Red Belly Pacu are difficult to have sex with until mature. The females are larger and have less red coloration on their bellies. Males are smaller, leaner, and have brighter coloration. It can be difficult to make these distinctions on an individual specimen. Observing a group makes sex easier.


Red Belly Pacu are susceptible to many common freshwater fish diseases such as Ich and Velvet. Keeping your water quality in top shape is critical for reducing your fish’s disease susceptibility. Excellent filtration is a must. This can come via canister filters or an external sump filtration system.

When adding new fish to your aquarium, keeping them in a quarantine tank (QT) for 8 weeks is important to watch for any disease symptoms.

Putting a fully grown Red Belly Pacu in QT can be challenging when they become large. This may be necessary as many disease treatments, especially those involving copper-based medications, must only be applied to the infected fish and not dispersed in a populated display tank. Make sure you have a properly sized quarantine tank available when needed.

Red Belly Pacu Tank Mates

Red Belly Pacu are docile fish that can get along with other large and docile species. They are so large that they may eat smaller tank mates, especially snails.

Compatible and Incompatible Tank Mates

Red Belly Pacu can coexist with other large and peaceful species like Oscars and can even hold their own with large Cichlids. It can be a good idea to include bottom-feeding fish that will eat the mess your Red Belly will make when feeding. This species is easily spooked, and aggressive fish might startle them enough to make them jump or slam against the tank wall.

Where can I find Red Belly Pacu for sale?

Red Belly Pacu are popular fish that are readily available from many fish stores and Internet sources.

Red Belly Pacu Price

Red Belly Pacu are affordable fish. A 2 to 3 inch specimen can be bought for around $12 USD.

Red Belly Pacu vs. Red Belly Piranha

Red Belly Pacu and Red Belly Piranha look similar from the outside. The Piranha has sharp pointed teeth, while the Pacu has squared teeth that resemble those of humans. Red Belly Pirhanas are carnivores, while Red Belly Pacus are herbivores.

The two species are easily confused. This gives the Red Belly Pacu its other name: the vegetarian piranha.

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