Piranhas: How Dangerous Are They?

The Piranha: Interesting Fish But Not a Good Choice for a Community Aquarium

Red-Bellied Piranha
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Adventure movies wouldn't be complete without scenes of people being stripped to the bone in seconds by ravenous piranhas in jungle rivers. And yet piranhas are also kept by some people as specimens in home aquariums. This contradiction may leave hobbyists wondering just how dangerous piranhas actually are.

In truth, it is the piranhas that are routinely eaten by people; only a few people have ever been eaten by piranhas. And yet, attacks on humans have indeed occurred, mostly in the Amazon basin. There are several hundred documented cases of attack, with a few ending in death. But of more than 20 piranha species, it is only the red-bellied piranha that is the subject of most of the man-eater legends.

How Dangerous Are They?

According to one study, red-bellied piranha attacks tend to peak in the dry season when food is scarce and water levels are low, which leads to heavier-than-usual concentrations of hungry fish. Still, even these dry season attacks are normally limited to small but painful nips to the hands and feet; fatal attacks are quite rare.

A piranha has powerful jaws with sharp teeth and is a formidable predator, but these fish usually only feed on other fish or wounded animals. The fact is that hungry piranha will bite at almost anything, even other piranhas. This conspecific predation happens frequently enough that piranhas have developed incredibly fast fin and body wall regeneration, with bites making visible healing progress literally overnight. This speedy regeneration is the topic of scientific study.

Fish expert Dr. H. R. Axelrod stated on network television that piranhas are not dangerous to people. Later he was asked to prove it, and prove it he did--by wading into piranha-infested waters wearing only swim trunks. Placing a large piece of meat on a fishhook, he dangled it in the water and waited. The piranhas tore into the meat but left Dr. Axelrod untouched.

Are Piranhas Legal?

Even though piranhas pose little danger to humans, they do present a danger to native fish species. For that reason, many states and countries restrict importing, breeding or even keeping them in aquariums.

Unfortunately, people have dumped fish they no longer want into rivers or lakes, but a piranha tossed into a river or lake can easily disrupt fish species that live there, thus damaging the ecology. The potential for a breeding population becoming established in our waters is real, and for this reason, some states instead choose to ban the fish even for use in indoor aquariums. 

Should You Keep Piranhas?

Even if they were legal, piranhas are not ideal aquarium fish. They cannot be kept with other fish because they are natural predators; they will eat all of your other species and sometimes even others of their own kind. Piranhas are also quite reclusive and rather skittish. Unless your tank is empty of all cover you won't see piranhas out and about very often.

Feeding time is when you will see the most action, and even then they may wait for you to leave the room before they decide to eat. Much like any aquatic predator, piranhas take single swipes at food. Their eating habits are much slower and relatively uneventful compared to the feeding frenzies depicted by Hollywood movie magic.

If you are serious about choosing to keep piranhas, study what they need to stay healthy. Piranhas are carnivores that prefer fresh food. They need a quiet habitat with places to hide, and should not be kept with other fish, even of their own species. And remember, because of the danger they present to local habitats, piranhas are not legal in many states; check your local laws before attempting to bring one home.