Piranha Teeth: Everything You Need to Know

Piranhas belong to a family of bony fish characterized by highly developed dentition. They’re cousins to the pacu fish, which has dentition eerily similar to human teeth. Unlike pacu teeth, which are flat, piranha teeth are very sharp and very effective. These fish are native to South America and can be found in the Amazon and Orinoco River basins. They’re illegal to own as pets in many areas, largely to prevent the risk of them threatening ecosystems if they were released into local waterways.

Here, we’ll learn all about piranha teeth and debunk a few of the popular myths surrounding these incredible fish. Then, we’ll take a look at how piranhas replace their teeth and how many they have in their mouths. After that, we’ll discuss the bite force of the piranha and whether or not they’re a real threat to humans. Finally, we’ll go over the teeth of the extinct megapiranha, which, by scientists’ estimates, grew up to three feet long!

Why Are Piranha Teeth So Sharp?

Popular myth might lead one to believe that piranhas have such wicked-looking teeth because they spend most of their lives defleshing large animals like cows and humans. 

Let’s stop right there.

First, piranhas aren’t obligate carnivores (animals that eat nothing but meat) at all — they’re actually omnivores, and those fearsome teeth serve as more than just steak knives.

Piranha teeth are scalpel sharp for two reasons: shredding up prey (like small fish), and scraping vegetable material up from the murky river or lake bottom. Their teeth are uniquely designed to shear flesh, but they’re also used to eat plant material.

How Many Teeth Do Piranhas Have?

Piranhas are one of the most feared of all bony fish, and their teeth are indeed efficient. They have a single row of extremely sharp teeth that run all the way around their mouth, top and bottom. Each tooth is tightly fitted to the next tooth. In fact, they’re so close that they actually overlap. 

Piranha teeth have three sharp, triangular cusps. The central cusp is by far the largest, and it’s razor sharp. The two smaller cusps on either side of the center cusp are used to lock each tooth into the teeth on either side of it. The razor-like teeth are wide from front to back, and narrow from side to side, like a straight razor.

When the piranha closes its mouth, the top and bottom rows of teeth act together to form a pair of scalpel-sharp scissors. A quick shake of the head, and whatever prey was unfortunate enough to find its way into the piranha’s mouth is no more. 

Replacing Teeth

Though there is no hard and firm number, piranha generally have around 20 teeth that can grow up to 4 mm long. Their bottom teeth are usually larger than their top teeth, and they have a pronounced underbite that forever highlights the fearsome teeth of the lower jaw.

Piranhas, like many toothed fish, are polyphyodonts — meaning they continuously replace broken or missing teeth throughout their lifetime. But, unlike sharks — which replace one tooth at a time — piranhas replace an entire side of teeth at a time.

Scientists have found that, because of the interlocking nature of piranha teeth, they cannot replace them one by one. Instead, the piranha loses all the teeth on one side of its mouth at once. These teeth are then immediately replaced by a brand new row of already interlocked, razor-sharp teeth.  

Piranha Bite Force

Piranhas aren’t just known for their sharp teeth; they’re also known for how hard they can bite. Though they’re small (usually between six and 12 inches), there’s nothing small about the piranha’s bite.

Piranhas have extremely tough jaw muscles, and all those jaw muscles are designed for one thing: biting. Piranhas can bite with a bite force of around 70 PSI. For comparison, rottweiler dogs bite with a force of around 350 PSI.

That might not seem like a lot, but considering that piranhas usually weigh less than 20 pounds and eat only small fish, it’s a bite force far outsized for this South American fish. The bite force works together with the razor-sharp teeth to act as one big biting machine. Piranha jaws are designed to grip and pierce small fish for swallowing whole, and to shear chunks off larger fish. But, they’re also effective for scraping up plant foods.

Are Piranhas Dangerous to Humans?

Given their fearsome reputation for defleshing man and cow alike in a matter of seconds, it’s no wonder so many people are afraid of piranhas. But, not to worry; the circumstances under which piranhas pose a danger to humans are very rare. Attacks are few and far between but usually include small children, hurt animals, and starved or extremely stressed piranhas. There have been a few instances of piranhas attacking and killing people, but for the most part, they would rather leave us alone.

Humans don’t fit the piranha ‘prey image’ — that is, what piranhas see as something to attack. They will only attack under the direst of circumstances. Still, given their extremely sharp teeth and predatory nature, it’s probably best not to go sticking your fingers in piranha-infested waters.

Ancient Piranha Teeth

Today’s piranha can bite through fish like a hot knife through butter. But would you believe that they’re actually much smaller than their extinct cousin, the megapiranha?

Megapiranha lived during the Miocene era, and is known from only one fossil fragment of a jawbone (complete with teeth). Scientists believe they grew up to three feet long, and — based on their jaws — may have had a bite force of up to 1,000 PSI. That’s a pretty big bite. But, based on their similarity to the modern piranha, scientists believe that these monstrous fish were also omnivores, and ate their vegetables just like today’s piranhas.