Are Sharks Fish? Why are Sharks Classified as Fish?

This question remains very simple until you start considering if “sharks are fish or mammal?” There’s quite a number of debates coming up on this issue. This is because some sharks’ characteristics match with fish while others with mammals.

So, are sharks fish or mammal? Sharks are fish! They are not mammals. As a fish, sharks are among the category of fish known as Cartilaginous fish. By understanding the characteristics of fish and mammals, you’ll easily figure out why sharks are fish. And, when we say sharks are fish, we mean all shark species!

That sharks live in the ocean is not what made them fish. Instead, they possess certain traits used in classifying fish.

No doubt, there are several marine mammals such as dolphins that look like sharks. However, this doesn’t make sharks mammals.

Let’s now find out More about sharks being a fish!

Why Do People Confuse Sharks to be Mammals?

First, there are several reasons why you can mistake a shark as a mammal. The most common reason is learning that sharks give birth to their young ones alive (viviparity).

Most people would consider this first in their definition of mammals, hence, the misconception of sharks as mammals. Note that not all shark species give birth to live young pups.

Another reason is the similarity in looks between sharks and dolphins a known marine mammal.

This leads to the question, “if sharks aren’t mammals, why do they look like dolphins?”

The truth remains that in the evolutionary family tree, sharks and dolphins are far apart. They share a similar body design which is a torpedo body and tail for pushing their body.

Well, it is likely that this design is ideal for fast-moving sea predators. Hence, these creatures only evolved into this design as a solution for living in the water.

In all, we shall now see the reasons why sharks are fish and not mammals.

Why are Sharks Classified as Fish?

To answer this question, we have to find out what fish have in common. Note that sharks fall into the type of fish known as Cartilaginous Fish.

This class includes skates and rays. They do not have bones and their skeletal system is made up of cartilages.

Now let’s compare some features of fish to sharks.

Fish Have Gills, What of Sharks?

The organ for gaseous exchange in sharks is the gill. So, yes! Sharks have gills.

Their gills help them to trap oxygen dissolved in water as water flow through their gills.

One major characteristic of all fish is that they live in water. Therefore, for them to survive underwater, they need to breathe. This is where their gills become very important.

Sharks have gills and this is a check when classifying them as fish.

Fish are Cold-blooded, Is this True of Sharks?

Certainly, sharks are cold-blooded or ectothermic. This means that they depend on the temperature of their surroundings to regulate their body temperature.

Most shark species are cold-blooded, however, there is the exception of those under the Lamnidae family. These have some traits of warm-blood.

Examples of these few shark species include the Great White Shark, Longfin Mako, and Shortfin Mako. Although, this does not make them any less a fish.

These sharks have the uncommon capacity to slightly raise their body temperature above that of the surrounding water.

For being mostly cold-blooded, sharks are classified as fish.

Fish have Scales, Do Sharks?

Sharks have tiny scales that may appear smooth in the eyes, but rough to touch surrounding their body.

These scales or dermal denticles not only serve as protection to the sharks against parasite attacks, but they also help to reduce drag in sharks as they swim. This makes them swim faster.

Since sharks have scales like most other fish do, they qualify as fish also.

Fish Have Well-developed Set of Fins, How about Sharks?

A typical fish would have a first and second dorsal fin, pectoral fins, pelvic fin, anal fin, and caudal fin (tail).

Most shark species have all these sets of fins. Their caudal fins help them to maintain stability while swimming, steer, boost, and swing their head.

When identifying a fish, fins serve as the most unique anatomical characteristic.

Do sharks have fins? Yes, sharks have fins.

Therefore, we say this feature also qualifies them as fish!

Why are Sharks Not Mammals?

Are you still wondering why sharks are not mammals?

Let’s compare the characteristics of mammals to that of sharks. Hence;

Mammals have Mammary Glands for Nursing Their Young Ones, Do Sharks?

Sharks do not have mammary glands; therefore, they cannot nurse their young ones. Mammary glands are only present in mammals which helps them in milk production. This is one major characteristic of mammals.

Here comes the tricky part, why some people consider sharks as mammals. Mammals give birth to their young ones alive and they get nourishment through the placenta (viviparous).

Some species of shark also give birth the same as mammals (viviparous). However, they do not have the capacity to nurse their young ones. This includes even the Nurse Shark.

Note that different species of sharks give birth in different ways. While we know that some give birth to their young alive (viviparous), some others lay eggs (oviparous), while the rest have their eggs hatch internally prior to delivering live pups (ovoviviparous or aplacental viviparous).

As sharks do not have mammary glands and cannot nurse their young ones, they are therefore not mammals.

Mammals have Hairs, Do Sharks?

Obviously NOT! Sharks do not have hair. The body of sharks is covered with dermal denticles, tiny tooth-like scales.

If you ask whether marine mammals such as dolphins also have hair, yes, they do. Cetaceans have some kind of hair at various parts of their body.

As for dolphins, they usually have a few whisker-like hairs protruding from the sides of their rostrum. Though they lose these hairs immediately after birth, the follicles would still be there.

The lack of hair in sharks is still a disqualification from being a mammal.

Mammals Breathe Air, Do Sharks?

Sharks do not breathe air; they do not have lungs. Instead, they make use of their gills for gaseous exchange in water.

Wait, do marine mammals also have lungs and breathe air? Yes! Marine mammals such as dolphins and whales have lungs and do breathe air.

They usually swim to the water surface at intervals to draw in air to their lungs using their blowholes. The blowhole is of similar functionality as the nostrils of the terrestrial mammals.

The blowhole is on top of the head. After breathing air, marine mammals close their blowhole and seize their breaths while inside water.

Sharks have different breathing mechanism using gills. This equally disqualifies them as mammals.

Mammals are Warm-blooded, are Sharks?

Sharks are generally not considered warm-blooded. Though there is the exception of the Lamnidae family.

Even with this exception, no shark species qualifies as a mammal.

Mammals are warm-blooded (endothermic). This means that they can regulate their body temperature independent of their surrounding temperature.

Most sharks also do not meet this criterion, hence, doesn’t qualify as mammals.

Mammals have Neocortex, Do Sharks?

The neocortex is the dorsal region (6-layered) of the cerebral cortex unique to mammals. This in simple definition is the mammalian cerebral cortex.

Do sharks have this in their brains? NO! sharks do not have a neocortex.

Though sharks have a relatively large brain to body ratio compared to most other fish.

As observed in mammals, the neocortex relates to higher functions such as consciousness, motor commands, language, spatial reasoning, and sensory perception.

If the neocortex is unique to mammals and not present in sharks, it disqualifies sharks as mammals.

Summarizing the Comparison

With our comparison, you can easily tell that sharks are Fish and not mammals. In fact, sharks are among the types of fish called Cartilaginous Fish.

Though there are other reasons why sharks are classified as fish and not mammals. However, the ones discussed should be able to convince you!

Why are Sharks Further Classified as Cartilaginous Fish?

Yes, sharks are fish, but among fish, there are different classes. The classes of fish include Bony Fish, Cartilaginous Fish, and Jawless Fish.

Cartilaginous Fish are fish of the class Chondrichthyes which includes sharks, rays, and skates. This group represents fish whose entire skeletal system comprises of cartilages.

Sharks belong to this group since they have their entire skeletal system built from cartilages.

Other groups such as bony fish of the class Osteichthyes comprises of fish with bony skeleton instead of cartilage. Examples include sturgeons, mackerels, eels, and sunfish.

For the Jawless Fish of the taxon Agnatha, they are a group of primitive vertebrates having no jaws as their name suggested. Examples include cyclostomes and other extinct related forms.

To therefore different these differences among fish, there is the need to further classify them.

In Conclusion

This page presents sharks as fish, detailing the reasons why they are so!

If you ever asked the question, “Are Sharks Fish or Mammal or Both?” Here you have your answer.

Sharks are NOT mammals nor both fish and mammal. Sharks are only in the class of FISH!