When looking at how animals are classified, it can get quite confusing, quite quickly. There are lots of words in Latin with many classifications and definitions.

So, are Piranhas mammals? In short, no, Piranhas are not mammals. Under the definitions in the animal kingdom, the classifications at the class level has the options of mammals, birds, fish, reptiles and amphibians. Mammals must be warm blooded, possess hair or fur and give birth to live young. The Piranha is scientifically a fish of the order of Characiformes, which are ray finned fish. They fall under the Chordata phylum as they have a spinal cord.

Definition Of A Mammal

Before we define a Piranha, the definition of a mammal is;

1. a warm-blooded vertebrate animal of a class that is distinguished by the possession of hair or fur, the secretion of milk by females for the nourishment of the young, and (typically) the birth of live young.

The Piranha is certainly a vertebrate animal, but there are some issues in the definition that are not representative of the fish.

Firstly, the Piranha is not warm blooded, it is technically classified as a cold blooded, poikilothermic vertebrate. This means that it gets its body temperature from its surroundings, and it does not internally regulate that temperature. If the temperature of the Amazon river is 78 degrees Fahrenheit on a particular day then that will be the temperature of the Piranha’s body.

Additionally, the Piranha does not possess fur, does not secrete milk, and they do not give birth to live young. All Piranha have scales, lay eggs and do not secrete milk.

So, by the definition of the word mammal, no, the Piranha is not a mammal.

So What Is A Piranha and How Are They Classified?

As part of the ‘domains of life’, and depending upon where you are in the world there are either 5 or 6 kingdoms.

In the USA the kingdoms that all life on earth fall under are Animalia, Plantae, Fungi, Protista, Archaea/Archaebacteria, and Bacteria/Eubacteria.

Many other countries, including the UK, Australia and India use the five kingdoms of Animalia, Plantae, Fungi, Protista and Monera.

Clearly, the two major kingdoms that get the majority of exposure are the Animalia kingdom and the Plantae kingdom. More commonly they are known as the animal kingdom and the plant kingdom.

All animals on earth fall under the classification of being in the animal kingdom, but you can obviously further classify animals, as some fly and others swim.

The classifications that further specify and identify a species are Kingdom, Phylum, Class, Order, Family, Genus, and Species.

The classifications for Piranha are;

Thus Piranha are a genus of the family Characidae, of the order Characiformes, of the class Actinopterygii, of the phylum Chordata of the animal Kingdom.

Characiformes are just the scientific way of saying a ray finned fish.

As you can see, the further down you do down the classifications you go, the closer you get to how to define a Piranha.

The Red-Bellied Piranha is a species, with the scientific name of Pygocentrus nattereri.

Conclusion

So, definitely, all Piranha are not mammals. Mammals are segregated as an option at the class level. Piranha are animals with a spinal cord, so that classifies their kingdom and their phylum.

The options at the class level are mammals, bony fish, cartilaginous fish, birds, amphibians and reptiles. It’s in this class that we can separate the Piranha away from being a mammal. 

Mammals must give birth to live young, possess hair or fur and be warm blooded. This clearly does not define a Piranha.

Piranha are a cold blooded, poikilothermic vertebrate bony fish of the order Characiformes and the family of Characidae.