Two of the most intimidating and recognizable predators on earth, piranhas and sharks share many similarities despite their different habitats, size, and feeding strategies. Piranhas are strictly a river and lake-dwelling species found in the Amazon Basin, while most shark species cannot enter freshwater.

Great white sharks give birth in warmer tropical or temperate waters, but their breeding behaviors and courtships are poorly understood.Piranha swimming
Shark (left) vs. Piranha (right)

Key Differences and Similarities Between Sharks and Piranhas

  • Appearance: Sharks have a more elongated, torpedo-shaped body than piranhas which are stubbier and triangle shaped. Instead of bones, sharks are made up of cartilage, while piranhas have skeletons made of bones like most fish.
  • Size: There are many different shark species, and their size can vary a lot from less than a foot long to over twenty feet. But the majority of species are significantly larger than a piranha which averages between six and twelve inches on average.
  • Habitat: Outside of a few unique species like the bull shark, sharks spend their entire lives in saltwater as their bodies are incapable of handling the difference in salinity though some can spend periods of time in brackish water near river mouths. Piranhas are the opposite, spending their entire time in the freshwater rivers and lakes of the Amazon.
  • Diet: Sharks are carnivores, subsisting on a variety of food sources depending on the species. They feed on other sharks, seals, sea lions, marine mammals, and smaller fish. They will even scavenge if given the opportunity. Piranhas are omnivores, able to eat both animal and plant matter. They primarily feed on the fins of other fish, insects, invertebrates, and whole fish. They can also metabolize plant material like figs and other fruits that fall into the water.

We’ll explore these differences and exciting facts about these ocean creatures below.


Sharks are elasmobranch fish, meaning they have cartilage instead of a bony skeleton. They are closely related to rays and skates and are some of the oldest creatures on earth, having emerged during the early Jurassic.


Sharks have five to seven gills and long, svelte bodies made for efficient traveling and bursts of speed that allow them to stalk and surprise their prey.

Bonnethead shark swimming
A bone shark with two dorsal fins and a swept-back caudal fin or tail

Most sharks have two dorsal fins, a taller one near the center of the body and a shorter one near the tail. On the underside are the pectoral flippers near the gills that are used for steering. Toward the tail are two more fins, the pelvic and caudal, that serve as skegs to stabilize and improve the shark’s tracking.


Sharks can be found in every ocean on Earth. Most species prefer temperate or tropical waters closer to the equator, but some species, like sleeper sharks and Greenland sharks, have evolved to live in polar waters. They are predominantly saltwater animals, although bull sharks have proven to be capable of spending extended periods of time in freshwater rivers with no adverse effects. 


You can think of sharks like an ocean-going garbage can. After millions of years, these carnivores have evolved to feed on an impressive collection of prey that includes fish, marine mammals, crustaceans, mollusks, and other sharks. Despite this flexible diet, shark attacks on humans are incredibly rare and are often a case of mistaken identity and not the result of the shark seeing the human as a food source.

Bull Shark leaping on the surface, a skill they utilize in streams.
Bull Shark leaping on the surface, a skill they utilize in streams.

Some of the largest sharks don’t feed on fish or mammals but are instead plankton feeders. These sharks don’t have teeth but instead are filter feeders in a manner similar to baleen whales.


Many shark populations have dropped drastically in the last century. Many species are poorly understood, and even basic life history facts like their lifespan and reproductive studies have not been determined. Sharks are commonly caught as bycatch for other fisheries and are also targeted for shark fin soup or because they’re viewed as competition for resources. Climate change and habitat destruction are exacerbating these problems. As of 2022, roughly one-third of all shark and ray species were considered threatened with extinction.


Piranha has a fearsome reputation that includes sensational stories such as a school consuming a cow in minutes. But piranha attacks are quite rare, and they feed on a diverse range of food sources as they travel through South America.



Most piranhas are between six and twelve inches in length, with the largest confirmed individual measuring twenty inches. The most recognizable feature of these little, triangle-shaped fish is their teeth.

Piranha close up
While stories exist of piranhas measuring more than two feet, most individuals are between six and twelve inches.

Piranhas have a single row of tightly packed teether on both the upper and lower jaw. The teeth are serrated, while well-developed jaw muscles allow piranhas to have the strongest bite of any of the bony fishes.


Piranhas can only be found in the freshwater environments of South America. They can be found in lakes, rivers, reservoirs, and floodplains. While not migratory, they will travel large distances depending on prey availability, water level, and reproductive reasons. Piranhas are schooling fish. It was long assumed they schooled for predatory reasons, but recent research shows that they form large groups for protection from their own predators.


Piranhas can feed on both meat and plants. Smaller fish, invertebrates, and opportunistic bites of larger fish are key parts of a piranhas diet. They can also feed on fruit when available such as figs.

Piranha teeth
Piranha used tightly packed, serrated teeth to nip at larger fish or grasp small fish.

The legend of piranhas skeletonizing a large mammal in minutes likely originated from an account by Theodore Roosevelt in 1913. After blocking off a portion of the river for several days, local fishermen pushed a cow into the river, and the ravenous piranhas quickly consumed it.


Piranhas are an important prey species source for several South American predators, including jaguars, dolphins, larger fish, and crocodiles. Their meat is considered good to eat, and they are a popular food source for South Americans. Despite this, piranhas are not considered threatened at this time, with the IUCN listing them under the category of “least concern.”


How many species of sharks are there?

There are 520 confirmed species of sharks, although this number continues to grow as scientists continue to discover subspecies and brand-new species. In total, there are over 1200 confirmed species of cartilaginous fish which include sharks, rays, skates, and chimeras.

How long do sharks live?

A shark’s lifespan depends on the species. Some have relatively short lives of less than twenty years. But whale sharks are believed to live over 100 years, while the Greenland shark is estimated to have a lifespan of more than 400 years.

Do piranhas attack people?

Contrary to their reputation, piranhas very rarely attack people. When attacks have occurred, the most common event is a few small nips. There have been a few fatalities over the years, usually involving small children or adults under the influence of drugs or alcohol.

Are piranhas poisonous?

Neither the bite of the flesh of a piranha is poisonous. Some Amazonian cultures consider the eating of predatory fish taboo. But piranhas are high in Omega fatty acids and are a popular dish either grilled or in soup throughout much of Brazil.

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