Still, the film made me wonder about these ill-reputed creatures. Herewith, a piranha primer.

Big (living) animals aren’t the usual target. Unless they are starving, as is sometimes the case during the dry season in the Amazon when water levels drop, piranhas rarely attack a much larger animal (such as you), though bites and lost toes do occur, and blood in the water does get them riled up.

It’s sometimes a piranha-eat-piranha world. During a feeding frenzy, piranhas sometimes tear each other up along with their intended prey. Then, cannibalism is common. (Why waste fresh meat?)

They’re good parents—at least initially. A mom may lay 600 eggs at once, dad promptly fertilizes them, and both parents guard the brood once it hatches. (Later, they might eat some of their young. But let’s not focus on the negative.)

Despite their scary looks, they’re actually cowards. Okay, that’s a bit unfair, but studies have shown that rather than congregating to hunt cooperatively, as was always believed, they join forces because they’re afraid of being eaten. They’re especially likely to band together—in schools as large as 1,000 fish— at times of year when predators such as caimans and dolphins are regularly present. Apparently, they’ve gotten the message (evolutionarily speaking) that there’s safety in numbers even if you yourself have really sharp teeth.

24 U.S. states have outlawed keeping piranhas as pets. The main concern isn’t the danger to human toes but that, if released into the wild, they’ll become established and outcompete or kill native species. As they prefer warmer water, their survival would be most likely in southern states. Cold kills them.

In states where piranha are legal to keep in aquariums, one particular species is a favorite. The red-bellied piranha, Pygocentrus nattereri, has a rosy tummy and shimmering scales. Pretty! The species is also known for its aggression, which for some enthusiasts is the whole point (apparently, it’s fun to watch a big fish quickly turn live bait into a bloody pulp).

Hollywood typecasts them. Piranhas have starred in at least four films, including Piranha 3D, all of which portray them as bloodthirsty man-eaters. Sample plot, courtesy of imdb.com: “Doctor Baines has been conducting genetic experiments on piranhas and has made them virtually unstoppable” (Roger Corman’s Piranha).

Theodore Roosevelt wasn’t a fan. In his 1914 book Through the Brazilian Wilderness, the president described seeing starving piranhas devour a cow carcass (probably placed in the water by local fishermen to guarantee a show). He called piranhas “the most ferocious fish in the world” that will “rend and devour alive any wounded man or beast; for blood in the water excites them to madness.” He further described the fish as “the embodiment of evil ferocity; and the actions of the fish exactly match its looks….” Later, he adds, “The only redeeming feature about them is that they are themselves fairly good to eat, although with too many bones.”

–Jennifer S. Holland

Piranha photographs by Frank Magallanes

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