Everyone who sees a photo for the first time asks the same question: “Are those teeth real?” Yes, they are. Opening a pacu’s mouth reveals something genuinely unsettling: neatly arranged, rounded, powerful teeth that look remarkably like a human’s. This giant of the Amazon is one of the most fascinating creatures in the underwater world, both for what it looks like and the story behind it.
Good news for those who want to see it up close: the pacu is one of the special residents of Emaar Aquarium & Underwater Zoo. No photos needed — you can see it in real size, live and in motion.
So what are those teeth actually for? Is the pacu dangerous? How is it different from a piranha? Let’s take a closer look at this extraordinary fish.
What Is the Pacu Fish?
Known scientifically as Colossoma macropomum, the pacu is a giant freshwater fish native to the Amazon and Orinoco river basins. It belongs to the family Serrasalmidae, the same family as the piranha, which is exactly why the two are so often confused. But the differences in both appearance and character are hard to miss once you know what to look for.
A piranha’s teeth are sharp and triangular, built for tearing flesh. The pacu’s teeth are round and flat, evolved to crack open hard seeds and fruit shells. In short, the pacu is not an aggressive predator. It’s more of a gentle giant wandering the Amazon forest floor in search of fallen fruit.
The name “pacu” comes from Portuguese, derived from the traditional local name given to this fish in South America. It is widely known by this name in the aquarium world.
Pacu Fish Facts
Scientific Name: Colossoma macropomum
Common Names: Pacu, Tambaqui, Giant Pacu
Family: Serrasalmidae (piranha family)
Natural Habitat: Amazon and Orinoco river basins, South America
Average Length: 70–100 cm in the wild; some individuals exceed 1 metre
Average Weight: 20–30 kg; largest recorded individuals reach 40 kg
Lifespan: 15–25 years
Diet: Primarily herbivorous (fruits, seeds, plants)
Water Temperature: 22–28°C
Water Type: Freshwater
Appearance and Physical Features
The pacu has a laterally compressed, wide, oval-shaped body. Healthy adults typically reach between 50 and 88 centimetres in length, and some individuals in the wild grow past a metre. When people think of freshwater fish they usually picture something small enough to fit in a bowl. The pacu is nothing like that. This is a giant.
Its upper body is usually a silvery grey, while the belly shows a warm orange-red tone, which earned it the nickname “red-bellied pacu.” Its scales are large and glossy, and in clean water conditions the body gives off an almost metallic shimmer.
But the feature that stops everyone in their tracks is the teeth. Open the mouth and you find two rows of rounded, flat, sturdy teeth arranged in a way that looks unmistakably human. These teeth evolved specifically to crack open hard fruit shells and large seeds. They are strong enough to break a walnut or a hazelnut without much effort.
Its fins are worth noting too. Wide pectoral fins make it a surprisingly agile swimmer. It may look slow and heavy, but when it wants to move fast, it can.
Natural Habitat
The pacu lives in the Amazon and Orinoco river systems of South America, home to the world’s largest freshwater ecosystems and an extraordinary diversity of life.
During the rainy season, the pacu does something remarkable. As Amazon rivers flood and spill into surrounding forests, the pacu swims between the trees, collecting fruits and seeds that have fallen from the branches. It becomes, in its own way, a fruit forager of the forest floor. Seeds it cannot digest pass through and are deposited far from where they were eaten, making the pacu an important seed disperser for the entire ecosystem.
In the dry season it retreats to the main river channel and survives on organic matter and small aquatic creatures. Hunger, heat, murky water — the pacu handles it all. It’s a tough fish.
Feeding Habits
The pacu is primarily herbivorous. In the wild, its diet consists mainly of fruits, seeds, aquatic plants and algae. It is particularly fond of figs, palm fruit and various Amazonian fruits. Its powerful teeth allow it to chew through shells that would be difficult for human hands to crack.
That said, the pacu is not strictly herbivorous. It will occasionally eat insects, small fish and zooplankton when it needs protein. Think of it as an opportunistic eater that prioritises plants but won’t say no to a good meal whatever form it takes.
In an aquarium setting, feeding is straightforward. Sliced fruit (banana, apple, orange), vegetables (courgette, cucumber, spinach), high-quality pellets or granules, and frozen or live shrimp all work well as part of its diet. Pacus that are fed consistently look vibrant and full of colour. A stressed or underfed pacu will show it quickly through dull, faded colouring.
One thing to keep in mind: the pacu grows fast. Underfeeding affects both its growth and its behaviour.
Behaviour and Temperament
Despite sharing a family with the piranha, the pacu is not an aggressive fish. In the wild it tends to be calm and shy. Dangerous behaviour toward humans is extremely rare; as long as it doesn’t feel threatened, it generally keeps its distance.
Because of its size and strength, keeping small fish alongside a pacu in an aquarium is not recommended. Not because it hunts them, but because it can accidentally injure or swallow them simply by moving around. It does well with similarly sized, peaceful species.
The pacu is also surprisingly intelligent. Our pacus at Emaar Aquarium prove it every day: they recognise their keepers, have learned feeding times, and don’t hesitate to come to the glass when visitors approach. Spend a few minutes watching and they start watching you back.
There’s also an urban legend worth clearing up. Over the years, various media outlets described the pacu as a dangerous fish that attacks men. These reports were largely exaggerated and based on misidentification. There is very little credible scientific evidence of the pacu intentionally attacking humans. It has strong teeth, yes, but they belong to a fruit lover, not a predator.
Pacu vs Piranha: What’s the Difference?
These two fish get mixed up so often it’s worth spelling out the differences clearly.
Teeth: The pacu’s teeth are round and flat, much like human molars. The piranha’s are sharp and triangular, built to cut through flesh.
Diet: The pacu is mainly herbivorous; the piranha is carnivorous and predatory.
Size: The pacu reaches 50–100 cm; the piranha usually stays between 20–35 cm.
Temperament: The pacu is calm and shy; the piranha is aggressive and hunts in groups.
Colouring: The pacu has a silvery-grey body with a red belly; the piranha has a silvery base with red or golden tones on the underside.
Similar looks, shared ancestry, but two very different fish in every way that matters.
Interesting Facts About the Pacu
There are a few things about the pacu that don’t get talked about enough.
In its natural habitat it plays a critical ecological role. Known as the “seed disperser” of the Amazon, it swallows hard seeds whole, carries them long distances, and deposits them through its waste. Some researchers have suggested that if the pacu were to disappear, the reproduction of certain Amazonian tree species could be at risk.
In many tropical regions, particularly in Southeast Asia and parts of Europe — people who could no longer care for their pacu have released them into local waterways. These fish can become invasive species in ecosystems they don’t belong to. Owning a pacu is a real long-term commitment.
A pacu can live up to 25 years. The fish that looks small and manageable when you first see it can grow into a 30 kg animal over time and will need proper care for decades.
In Brazil and Colombia, the pacu means something else entirely: a prized ingredient in local cuisine. Fresh pacu is a staple at family gatherings and special occasions throughout Amazonian communities.
Frequently Asked Questions
Is the pacu fish dangerous?
No. The pacu is not dangerous to humans. Its teeth are strong but used primarily for crushing plant material and seeds. As long as it is not provoked, it poses no threat.
Is the pacu the same as a piranha?
No. They share the same family but are different species with different teeth, diets and temperaments. The piranha is a sharp-toothed predator; the pacu is a round-toothed, mostly herbivorous fish.
Why does the pacu have human-like teeth?
Its teeth evolved to crack open hard seeds and fruit shells, which required a strong, rounded structure. That structure happens to look remarkably like human molars — a coincidence that surprises biologists and visitors alike.
How long does a pacu live?
In good conditions, between 15 and 25 years.
How big does a pacu get?
In the wild, up to 100 cm in length and 40 kg in weight. In aquarium conditions it tends to stay a bit smaller, but it is still a large fish.
What does a pacu eat?
Mainly fruits, seeds, aquatic plants and algae. It will also eat insects and small fish from time to time.
Want to see the pacu in person? It is one of the resident animals here at Emaar Aquarium & Underwater Zoo. Come see this Amazon giant up close, watch it during feeding time, and explore hundreds of other fascinating creatures. We are open every day.
