Pacu fish (Colossoma macropomum)

Pacu fish or tambaqui (lat. Colossoma macropomum) – is one of piranha family known for its lust for blood. But unlike its “cousins” and despite a strong and massive body, colossoma prefers plant food and belongs to herbivorous class.

There are a lot of different fishes with pacu name, however quite often their classification is rather confusing. Black pacu is an interesting, not demanding and easy in care and feed fish, which has its kind of intelligence. Sounds like an ideal aquarium fish, doesn’t it?

However, the biggest problem in care is that it grows fast to become a huge fish and rather quickly it outgrows even very spacious tanks. The problem is, that on the market the fish is quite often sold as juveniles and then mistaken for piranha.

Although these fishes really look alike, fish is less aggressive and not that predatory, since it feeds on plant food. But it doesn’t eliminate the fact that pacu will eat any small fish in a tank without any doubt.

Is definitely not a fish for everyone.

To keep just one juvenile species you’ll need 300 gallons tank and for the adult fish – about 650 gallons.

Such a tank requires very thick glass, since if fish gets scared it can break the glass.

Habitat in the wild

Colossoma macropomum is the largest characin representative in South America. The fish inhabits in the Amazon and Orinoco river basins.

As a rule pacu prefers solitary. Juveniles feed on phytoplankton, insects, snails, the adult are mainly herbivorous, they feed on fruits and other plant food.

Juveniles stay in blackwaters up to the time they become reproductive.


Max size is about 108 cm, but usually it’s about 100 cm (40 in) long and it weights up to 40 kg. The lifespan is about 20 years.

The appearance resembles piranha – the body is high, laterally flattened with big eyes.

The body color varies from black to gray with some variations. About 10% of the body mass is fat. The fish has square human-like teeth that makes them incredibly similar to the human ones.

Instead of piercing the victim with its teeth and tear it apart, pacu bites its prey to the bones and tears parts from it, also the fish can easily crack nuts.

Difficulties in keeping

It is a very large fish and it’s better to be kept in very spacious tanks – not everyone can afford to have such a fish at home, although it’s rather not demanding and easy in care.

It’s not very strict to water parameters, they shouldn’t be too extreme, the same is about feed.


Fish is omnivorous and in the wild it feeds on fruit, corn, insects, snails, spineless species and carrion. Plant food should prevail in diet, however the fish will eagerly eat worms, blood worms, tubifex.

But too much of protein leads to the lipoatrophy quite fast. As for the small fishes – they are also treated as feed, so don’t keep pacu in a tank with them.

Keeping in a tank

Scientific NameColossoma macropomum
Common NamePacu fish, paku fish, paco fish, black pacu
Tank size650 gallons and more
Temperature75–81 °F (24–27 °C)
Sizeup to 100 cm (40 in)
Lifespanup to 20 years

The main requirement is a very large tank, for adult species from about 2 tons capacity. If you can afford such a tank – here the difficulties end, since the fish isn’t a demanding one, has a persistence to diseases and eats any feed.

The only thing is, that they require a very strong filtration, because they pollute tank water a lot.

The fish inhabits in the middle water layers and it needs some free space to swim. The best tank decorations are snags and large rocks, don’t even try to put any plants – they are feed for fish.

Black pacu is a bit timid – any unexpected movement causes panic attack and the fish starts tearing around the tank, hitting the objects and glass walls.

The tank water temperature should be constant about 75–81°F (24–27 °C), dGH до 20°, pH about 6-8 with strong filtration, aeration and regular water renew. Not for long the fish will do with water temperature decrease up to 22 °C.

Compatibility and tank mates

Adults are loners, but they aren’t aggressive, however the juveniles are more troublesome and aggressive. The adults feed on any small fish that they can swallow, but they won’t do any harm to large fishes.

The best tank mates are the same large fishes (Tiger oscar, Green terror, Managuense cichlid) or you’d better keep them alone in the tank.

Sex differences

Male has more sharp dorsal, its anal fin has pins and the fish itself is brighter colored than the female.


Breeding is impossible in a tank because of the fish size. All species that are on the market are bred in ponds or at farms.