Piranhas are freshwater fish found only in the river systems of central and southern South America. They prefer tropical rivers and streams, particularly those with murky water and plenty of vegetation to hide in. These fish have strong jaws lined with sharp, pointed teeth, which allow them to bite into their prey and tear flesh from bone. Piranhas are one of the most feared fish species, but do they deserve their reputations? How big do they actually get, and are the largest piranhas ever really dangerous man-eaters? Read on to find out.
Piranha Species
There are between 30 and 60 piranha species.
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It is estimated that there are between 30 and 60 species of piranha. Piranhas are part of the subfamily Serrasalminae in the family Serrasalmidae. They are part of the order Characiformes, which also includes tetras. Carnivorous piranhas belong to four different genera, including:
- Pristobrycon
- Pygocentrus
- Pygopristis
- Serrasalmus
Most piranhas only grow to about 12 inches long and weigh less than 2 pounds, but a few species can grow significantly larger. The largest piranha species belong to the Pygocentrus genus and the Serrasalmus genus, discussed below.
The Largest Piranha Ever
San Francisco piranhas can weigh up to 8 pounds.
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Some claim that the largest known species of piranha is the Rio São Francisco piranha (Pygocentrus piraya), also known as the San Francisco piranha or the piraya piranha. The San Francisco piranha’s average weight is around 5 to 8 pounds. They regularly measure between 12 and 14 inches. Some claims suggest they can reach 20-24 inches in the wild, but no specimens of this length have been scientifically verified. According to the International Game Fish Association (IGFA), the world record Pygocentrus piraya was 7 pounds and 6 ounces. No length was provided. The piranha was caught by angler Russell Jansen in the Amazon River Basin in Brazil in 2009.
Another contender for the largest piranha ever is the redeye piranha (Serrasalmus rhombeus), also known as the black piranha. They typically grow to around 13 inches on average and have a maximum weight of around 6.6 pounds. However, the IGFA world record Serrasalmus rhombeus is 8 pounds and 7 ounces. Guinness World Records lists the length of this catch as 19.5 inches, with a girth of 20.5 inches. Angler Russell Jansen also caught this record-breaking piranha in the Amazon River Basin in 2009.
Are Piranhas Dangerous to Humans?
Despite their menacing appearance, piranhas are generally not dangerous to humans.
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Piranhas have exaggerated reputations due to their razor-sharp teeth, partially carnivorous diet, and the horror stories that have been told about them over the years. Former president and adventurer Teddy Roosevelt is responsible for some of their bad press. During a visit to South America, he saw a cow torn to shreds right in front of him, leading him to describe it as normal behavior when he wrote about his experiences. In the James Bond film, “You Only Live Twice,” the villain feeds a henchman to piranhas. There is also a horror film franchise named after these unfortunate fish.
However, the piranhas Teddy Roosevelt was shown had been rounded up and starved. While some piranha species form large schools, this is primarily for protection, not for hunting. Yes, piranhas can go into feeding frenzies, but only when they are extremely hungry. Many piranha species do not eat meat at all. Even those with a more carnivorous diet do not eat live humans. The few documented instances occurred after death by other means. They rarely ever even eat large animals. Unprovoked attacks on humans are extremely rare. Piranhas may become aggressive when defending their young, when starving, or when confused about whether human fingers and toes are prey, but in most cases, attacks result in only minor injuries.
The Megapiranha
A 2-pound black piranha can generate a bite force of around 35 times its own weight.
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Giant piranhas are not just creatures from horror movies. They once roamed the waters of South America, much like the species we have today. Megapiranha paranensis is an extinct species that lived over 10 million years ago in the Late Miocene era. Research suggests they were able to reach over 4 feet in length and weigh up to 30 pounds.
Only the teeth of the holotype specimen have been discovered so far, but researchers believe Megapiranha had a bite force of up to 50 times its own weight. The team used the size and jaw structure of the black piranha to determine the size of the Megapiranha and reconstruct its bite. On average, black piranhas only weigh around 2 pounds, but they can generate over 70 pounds of force, or 35 times their weight.
