Vegetarian piranhas are the Amazon’s champion gardeners
This monstrous fish is a tambaqui, a close relative of the piranha. Fortunately, it doesn’t share its cousin’s flesh-eating lifestyle. Instead, the 30-kilogram tambaqui (or pacu) is a vegetarian. It swims through the flooded forests of the Amazon, eating fruits that drop from the overhanging trees. In doing so, it acts as an vehicle for the Amazon’s seeds, carrying them to distant parts of the jungle within its gut.
This is a role that we normally associate with birds or monkeys, but Jill Anderson from Cornell University has found that the tambaqui is a champion seed carrier. It can spread seeds over several kilometres, further than almost any other fruit-eating animal on record.
Many plants in the Amazon have adapted to use fish as seed vehicles, and start producing fruit when the forests undergo their annual floods. And a vehicle as large as a tambaqui can carry a lot of seeds. When Anderson looked in the guts of 230 of these fish, she found 700,000 intact seeds from 22 different species.
To find out what happens to these seeds, Anderson tagged 24 tambaquis with radio transmitters and tracked them for several days using canoes. She also fed captive fish with fixed amounts of seeds to see how long it took before the fish expelled them.
Her data showed that the fish carry seeds over long distances, around 330-550 metres away from the parent plant on average. That compares favourably with small birds and monkeys, which tend to process the seeds through their guts more quickly. The fish give the seeds a more leisurely passage, and the larger ones do so especially slowly. This means that 5 per cent of the seeds are carried for a few kilometres, and some even end up 4 or 5 kilometres away. That’s much further than virtually all other seed-carrying animals, save for the Asian elephant or the African hornbill.
When the fish finally excrete the seeds, they deposit the vast majority of them in the right places – floodplains where they can germinate once the waters recede. Indeed, it seems that seeds find it slightly easier to germinate after a voyage through the tambaqui’s innards.
Anderson thinks that she’s underestimating the role of these giant fish. Over the course of her study, she lost track of three of them, probably because they outswam the scientists’ canoes. And the fish that she did catch were very small – just 2 kilograms in weight, compared to the maximum 20 to 30 kilograms of some adults. These full-grown giants could probably carry seeds much further.
That hints at a bigger problem. Tambaquis are severely overfished and their numbers are falling. For example, in Brazil’s massive Manaus fish market, over a third of the fish on sale are tambaquis. The biggest individuals are the most valuable catches and in some areas, the average size of the population has shrunk by 90 per cent. This may be why Anderson failed to catch adults anywhere near the reputed maximum size.
Other species of fruit-eating fish are facing similar problems. So fishermen are not only depriving the Amazon of some of its most effective seed dispersers, they are also taking the best carriers out of the game. In doing so, they are disrupting alliances between fish and plants that have been going on for millions years. And they risk the future of the same flooded forests that provide them with their livelihoods.
Reference: Anderson, Nuttle, Saldan a Rojas, Pendergast & Flecker. 2011. Extremely long-distance seed dispersal by an overfished Amazonian frugivore. http://dx.doi.org/10.1098/rspb.2011.0155
Photos by Kirk Winemiller (fish) and Jill Anderson (canoe)
More on fish and their environment:
- Evolving guppies shape their environments
- Bearded goby munches jellyfish, ignores toxic gases, is generally very hard
- Restoring predator numbers by culling their prey
- Human-induced evolution reverses for shrunken fish once fishing stops
- Farmed salmon decimate wild populations by exposing them to parasites
Go Further
Animals
- These 'trash fish' are among Earth's most primitive animalsThese 'trash fish' are among Earth's most primitive animals
- These photos are works of art—and the artists are bugsThese photos are works of art—and the artists are bugs
- The epic migration of a 6-foot long, 200-pound catfishThe epic migration of a 6-foot long, 200-pound catfish
- Frans de Waal, biologist who studied animal emotion, dies at 75Frans de Waal, biologist who studied animal emotion, dies at 75
Environment
- Are synthetic diamonds really better for the planet? The answer isn't clear-cut.Are synthetic diamonds really better for the planet? The answer isn't clear-cut.
- This year's cherry blossom peak bloom was a warning signThis year's cherry blossom peak bloom was a warning sign
- The U.S. just announced an asbestos ban. What took so long?The U.S. just announced an asbestos ban. What took so long?
- The most dangerous job? Inside the world of underwater weldersThe most dangerous job? Inside the world of underwater welders
- The harrowing flight that wild whooping cranes make to surviveThe harrowing flight that wild whooping cranes make to survive
History & Culture
- Meet the powerful yokai that inspired the demon king in ‘Demon Slayer’Meet the powerful yokai that inspired the demon king in ‘Demon Slayer’
- A surprising must-wear for European monarchs? Weasels.A surprising must-wear for European monarchs? Weasels.
- Meet the woman who made Polaroid into a cultural iconMeet the woman who made Polaroid into a cultural icon
- Inside the observatory that birthed modern astrophysicsInside the observatory that birthed modern astrophysics
Science
- LED light treatments for skin are trendy—but do they actually work?LED light treatments for skin are trendy—but do they actually work?
- NASA smashed an asteroid. The debris could hit Mars.NASA smashed an asteroid. The debris could hit Mars.
- Humans really can have superpowers—scientists are studying themHumans really can have superpowers—scientists are studying them
- Why engineers are concerned about aging infrastructureWhy engineers are concerned about aging infrastructure
Travel
- 2024 will be huge for astrotourism—here’s how to plan your trip2024 will be huge for astrotourism—here’s how to plan your trip
- Play and stay in the mountains of eastern Nevada
- Paid Content
Play and stay in the mountains of eastern Nevada - This couple quit the city to grow wasabi in Japan's mountainsThis couple quit the city to grow wasabi in Japan's mountains