Head to head
Piranha vs Shark
Both animals star in the same kind of nightmare, water that suddenly boils with teeth. In reality they are wildly different fish living in different worlds, and both are far less dangerous to people than films suggest.
| Piranha | Shark | |
|---|---|---|
| Skeleton | Bone | Cartilage |
| Water | Fresh water, tropical South America | Marine (a few enter fresh water) |
| Size | Usually under 50 cm | 20 cm to 12 m by species |
| Diet | Omnivore: fish, fins, insects, fruit, seeds | Carnivore; a few are plankton filter feeders |
| Group behaviour | Shoals for defence, not pack hunting | Mostly solitary; some feed in loose groups |
| Teeth | One interlocking row, replaced in blocks | Many rows, continuously replaced |
| Danger to people | Rare defensive nips; deaths extremely rare | Under 10 deaths a year worldwide |
| Age of the lineage | Within the bony fish radiation | Over 400 million years |
Piranha vs Shark: common questions
Could piranhas and sharks ever meet?
Essentially never in the wild. Piranhas live only in the fresh waters of tropical South America, in rivers, oxbow lakes, and flooded forest, while almost all sharks are marine. There is a narrow overlap in that the bull shark can travel far up rivers, including the Amazon, and has been recorded thousands of kilometres inland, so in the lower and middle Amazon a bull shark and a piranha could in principle be in the same stretch of water. But it would be a curiosity, not a contest, since a bull shark is many times the size of a piranha and the two are not adapted to interact.
Which has the stronger bite?
Relative to body size, the piranha, and by a wide margin. The black piranha bites with a force of around 320 newtons, roughly 30 times its own body weight, one of the most powerful bites for its size ever measured. In absolute terms, though, a large shark is not close. A big great white or bull shark can bite with several thousand newtons, enough to shear through bone and cartilage, simply because it is a far larger animal with a far bigger jaw and jaw muscles. The piranha's bite is remarkable engineering at a small scale; the shark's is remarkable raw power.
Are both piranhas and sharks endangered?
Neither is threatened as a whole group, but the situations differ. Piranhas are generally common and widespread across South American rivers, several are important food fish, and none is currently listed as globally threatened, though dams and deforestation alter the flooded-forest habitat many rely on. Sharks are a much bigger conservation concern; while there are hundreds of species and many are stable, roughly a third of assessed sharks and their relatives are threatened, mainly from overfishing for meat and fins and from bycatch, and several large species have declined by 70 per cent or more. So the group that frightens people most, sharks, is the one actually in trouble.