Like a scene right out of a Hollywood horror flick, a video published online this week shows a river in Brazil practically boiling over with feeding piranhas.
The video may make swimmers everywhere (or at least in South America) recoil in horror, but piranhas are rarely dangerous to people, says Zeb Hogan, a National Geographic fellow and professor of biology at the University of Nevada, Reno.
The toothy, omnivorous fish are found throughout South America, where people often wade or swim around them without being bitten, says Hogan.
Such a situation was famously chronicled by Theodore Roosevelt during an expedition to the Amazon in 1913-14, when starved piranhas trapped in a small pool shredded a whole cow carcass in seconds. (Watch piranhas devour an egret chick.)
Fishermen are occasionally bitten, and there have been some recent reports of attacks by piranhas and related fish in South America, including one death, “but these events are extremely rare,” says Hogan.
The fish in the video might be particularly aggressive if they've been fed regularly by people, Hogan says. Piranhas congregating to catch an easy meal would build up in large numbers, causing them to act just as they do when trapped in a small pool.
The area filmed might be a fish-cleaning station, or perhaps a planned act to amuse tourists, Hogan speculates. (Learn about the man who smuggled 40,000 piranhas.)
The person who posted the YouTube video has not responded to a request for more information about the scene that was recorded.
Piranhas play an important ecological role as scavengers and predators in their native rivers, says Hogan. They will often resort to cannibalism if food gets scarce. It's unknown how many species of piranhas exist, with estimates ranging from 30 to 60.
“I've been swimming dozens of times in rivers where piranha were very abundant and I've never been bitten,” adds Hogan.
Source: National Geographic
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