Why pacu are so important to the rainforest

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The dramatic decline of the pacu in their native waters could have severe consequences for the Amazonian rainforest.

The fruit eating pacu, Colossoma macropomum, also known as ‘tambaqui’ has been found to disperse seeds further than nearly any other animal as they can hold the seeds for up to 12 days in the gut.

This means that some fish excrete seeds nearly 3.4 miles from the 'mother' tree. Only the Asian elephant and the African hornbill have been shown to be able to transport seeds further in their guts than the South American fish at a distance of four miles.

The study by Duke University radio-tagged 24 pacu and analysed the stomach contents of 230. They found almost 700,000 seeds from 22 different species of tree and lianas and that the average distance of dispersal was 0.3-0.5 km but with potential for the seeds to be dispersed even further as they swam out of the range of the receivers.

Overfishing could have real consequences for the range, distribution and genetic variety of the Amazonian wetland as populations of the fish have declined by 90% since the 1970s.

Lead scientist Dr Jill Anderson of Duke University is quoted: "We don’t really know what the role of the fish is, relative to the other seed dispersing species, but my guess is they are very important in maintaining diversity. They could be really important in structuring this community."

The tagging was carried out in Peru where the fish is known as gamitana. During the 1970s tambaqui were an "extremely commercially important" species in the Amazon and in the Manaus fish market in Brazil they comprised up to 40% of all the fish on sale.

However in the last 40 years the populations have fallen and the average size of the fish has also decreased which will have a knock on effect as the bigger fish can transport the seeds further.

For further information see the paper: Anderson, Nuttle, Saldan a Rojas, Pendergast and Flecker. 2011. Extremely long-distance seed dispersal by an overfished Amazonian frugivore.