Are sharks mammals or fish? It may seem like an easy question, but it does catch a lot of people out. In this article, we’ll take a look at what makes a shark a fish, rather than a mammal …
Are Sharks Mammals or Fish?
Sharks are fish, not mammals.
In order to find out why this is, we need to learn a bit more about what makes a mammal a mammal … and what makes a fish a fish!
So What Are Mammals?
Mammals are a large group of diverse animals that all have certain characteristics in common. One of these characteristics is that female mammals produce milk to feed their young.
In fact, the word ‘mammal’ comes from the scientific word for the part of a female animal’s body that produces milk; the mammary gland.
Sharks don’t feed their young with milk, and therefore aren’t mammals.
Other characteristics that all mammals share include being warm-blooded and having hair.
Being warm blooded means that an animal is able to regulate its own body temperature (by shivering, etc.) in order to maintain a suitable temperature.
The scientific term for a warm-blooded animal is endotherm.
Sharks are cold-blooded. A shark’s body is unable to control its own temperature, and is reliant on external conditions.
The scientific term for a cold-blooded animal is ectotherm.
Whales Are Mammals, Sharks Are Fish
… Wait! Whales are mammals, they look like sharks … and they don’t have hair!
In fact, whales do have hair … but not much of it. The young of some species have hair before being born. Some whales have hair follicles around their mouths.
Sharks don’t have hair. Their bodies are covered with tough scales that enable them to swim quietly and efficiently.
The fact that whales – some of which look a little like sharks – are mammals confuses people into thinking that sharks may be mammals too.
Is A Shark A Mammal? Live Young
Another mammalian characteristic is giving birth to live young (rather than laying eggs).
… Hold on, not all mammals give birth to live young – platypuses lay eggs! I read it here: Platypus Facts.
Well spotted! Platypuses, and four species of echidna (spiny anteaters), are mammals that lay eggs. These five species are known as monotremes. They’re the only mammal species that lay eggs!
Like mammals – and unlike many fish – many sharks give birth to live young. So in this respect sharks are similar to mammals.
However, there are differences in how the unborn sharks receive nourishment while they are growing inside the mother.
Are Sharks Mammals: Breathing
Mammals breathe using lungs, whereas most fish (including sharks) breathe with gills. Gills are organs that extract oxygen from water.
So Are Sharks Mammals?
As we’ve found, although most sharks do give birth to live young – as opposed to laying eggs – they lack many other mammalian characteristics.
Sharks don’t feed their young with milk, neither do they have hair or lungs. Sharks are cold-blooded, whereas mammals are warm blooded.
This all means that sharks definitely aren’t mammals!
Sharks Are Fish
Let’s look at what makes a shark a fish…
Fish are cold-blooded vertebrates (animals with a backbone) that have gills (although some fish can breathe using other methods).
… Sounds like a shark to me!
There are 3 main types of fish: bony fish, cartilaginous fish, and jawless fish.
What kind of fish is a shark?
Let’s look at the different types of fish to find out where a shark belongs …
Jawless fish include hagfish and lampreys. They are eel-like fish, with long, thin bodies. As their name suggests, they don’t have proper jaws – so sharks definitely aren’t jawless fish!
95% of fish species are bony fish. Bony fish have skeletons made of bone. Most bony fish have a swim bladder, which is a gas-filled organ that controls the fish’s buoyancy.
A shark doesn’t have a swim bladder, and has to swim to get to the required depth. Sharks aren’t bony fish.
A shark’s skeleton is made of cartilage, rather than bone. (Cartilage is like bone, but more flexible.)
This means that sharks are cartilaginous fish.
Are Sharks Mammals or Fish?: Conclusion
Are sharks mammals or fish? On this page we’ve found that sharks are not mammals due to a number of reasons:
- Sharks don’t produce milk to feed their young.
- Sharks are cold-blooded (ectothermic) and cannot regulate their own body temperatures.
- Sharks don’t have lungs, and breathe using gills.
- Sharks don’t have hair. Their bodies are covered in hard scales.
We’ve also found that sharks are fish.
In addition, because they don’t have swim bladders, and skeletons made of cartilage rather than bone, we’ve found that sharks are cartilaginous fish.
Now find out the answers to more animal questions!
Other mammal pages:
- Mammals: An Introduction
- What Is A Mammal?
- Types of Mammal
- Mammal Evolution
- Is a bird a mammal?
- Is a dolphin a mammal?
The scientist responsible for much of the way we think about animal classification is Swedish naturalist Carl Linnaeus (1707–1778). The Linnean Society is the world’s oldest biological society, and is named after him.