Underwater gardeners: Pacu

Pacu fish are one of the main distributors of tropical seed in South America. They have powerful jaws and strong teeth that can crack open hard rainforest nuts and take them to new locations. This process is crucial to rainforest survival through diversity and regeneration.

Sowing seed

Just like birds and mammals, seeds pass through the pacu, but are not fully digested. Instead, the hard seed coat (testa) is softened and the seed falls to the riverbed ready to germinate.

Crucially, the seeds land some distance from the parent tree. This produces a mixed planting pattern and supports a richer diversity of animal and plant life.

This seed dispersal also supports rainforest regeneration that relies on a constant input of new trees. The capacity for land to regenerate is critical to maintain soil stability (with vegetation) and recover from deforestation.


Traditionally, pacu are an important food source for indigenous people living in the rainforests. They are also nationally important to South American countries and are farmed commercially.

However, Pacu are becoming harvested at unsustainable rates and their population is falling. With their importance to local ecology, this is likely to seriously affect rainforest habitats and the Amazon River.

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At a glance


Amazon and Orinoco Rivers in tropical South America


Mainly seeds and nuts; occasionally small fish and plant material. They store high-energy oils and live on this during the dry season when there is little food


Length: 1m (3’ 3’’)

IUCN conservation status

Not evaluated, but vulnerable with increased hunting and changes in the Amazon River
What does this mean?

Scientific name

Colossoma macropomum

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