Shark Species

What Makes a Shark a Shark?

what makes a shark a shark

The world beneath the water is the home of various creatures of different shapes and sizes. The one toothy, fearsome creature in this habitat is a Shark. The Sharks are one of the most skillful predators of the Ocean. They belong to the family that evolved 500 years ago and their ancestors roamed in the sea even before the Dinosaurs on the earth. They are placed in the class Chondrichthyes, which includes the fish and all the cartilaginous skeletons. The Sharks live in water, breathe through gills, and have fins like other fish. 

Have you ever wondered what is Shark? Is a Shark considered a fish? What makes a Shark a Shark but not another fish? In this comprehensive tutorial, we will discuss the following details:

What Are Sharks?

Sharks belong to the class Chondrichthyes and subclass Elasmobranch; it includes Skate, rays, and chimeras. They live in all the water around the world from deep to shallow water and have a wide range of adaptations that make them the best for their environments. They come in all sizes; from the smallest Shark (a dwarf lantern shark, which is equal to the palm of your hand) to the largest Shark (Whale Shark, the biggest fish in the world which measures about 46 feet).

There are almost 500 species of Sharks, some are speedy while some are slow, some sharks feed on Plankton and others feed on other fish. Most Sharks have streamlined bodies while others have falter bodies like rays.

Fast Facts of Sharks

Phylum: Vertebrates

Class: Chondrichthyes

Key Features: Torpedo-shaped body, triangular scales, razor-like teeth, and a strong sense of smell.

Habitat: Sea and Oceans

Diet: Feed on plankton and other vertebrates or invertebrates

Size: 7 to 32 feet

Weight: 1 Ounce to 20 tons

What Makes a Shark a Shark?

The Sharks live in water and breathe through gills but there are a few major differences between the Sharks and fish. Here are a few unique physical features of Sharks:

1: Bone Vs Cartilage

The most prominent feature difference between Sharks and other fish is the skeleton. The skeleton of fish is made up of bones while Sharks have a soft skeleton, which is made up of cartilage similar to the structure of the nose and ear of humans. The Sharks and rays are the only fish made up of this skeleton. The cartilage has lower density and is both durable and flexible helping the Sharks to swim better.

2:  Gill Slits

The Gills are the respiratory organ of the fish, the water flows through them and as a result, the gases are exchanged (Oxygen is absorbed and carbon dioxide is released). The Sharks have gill slits instead of flappy gills. They keep their mouths open while swimming to keep the water flowing through their Gill slits. In Sharks, the Gill slits are found on both sides of their bodies while in rays the gill slits are present on the underside of the body.

In Mostly fish, there is only one Gill, while in Sharks there are five to seven gill slits. Most Shark species have five-gill slits, but few have six or seven.

3: Fins For Swimming

The Sharks have various fins that are not present on any other fish. Each fin of the Shark performs a specific function. The Caudal fin also known as tail fin helps the Sharks in swimming. They move the Caudal fin side by side while swimming. 

The other fin is the Dorsal fin, the big scary fin located on the top of the Shark. The Dorsal fin prevents the Shark from rolling and maintains the balance.

The fish have less functional Pectoral Fins, on the other side the Sharks have well-developed Pectoral Fins. The Sharks use the Pectoral Fin lifting its body and steering.

The Fins and tails of the Shark and fish vary greatly. The faster Sharks like Shortfin Mako have short crescent-shaped tails while the slower moving Sharks have longer thinned tails.

4: Teeth That Regrow

The Sharks are born fully equipped and they have so many rows of teeth and only the front row of teeth are functional. The Teeth of Sharks are made of dentin, the tissue that is harder than the bone. Depending on the species and diet of the Sharks, the teeth have various shapes and sizes. They never run out of teeth; If the Shark’s teeth fall out, they will be replaced within 24 hours, and this phenomenon is known as revolver dentition. Most Sharks lose 30,000 teeth in their entire life. 

On the other hand, the bony fish has only one set of teeth and if they lose their teeth, it will be very slow to replace the broken teeth.

5: Dermal Denticles 

Sharks have unique skin in the fish world. The fish skin is covered with scales, while the Sharks have tooth-like scales on their bodies known as Dermal Denticles. The denticles are spread all over their bodies which reduces the drags and helps them swim more effectively. The dermal denticles vary in shape from species to species. As Sharks grow, they shed their denticles and replace them with larger ones.

6: Body Shape

Although the fish and Sharks are similar, they still have a few differences in their body shapes. The fish have an oval-shaped head, and the Sharks have a triangular-shaped head. Sharks have generally fusiform bodies ( rounded and tapered at both ends). The fish have streamlined bodies, and the head and tail of their bodies are generally smaller than the rest of the body.

7: Egg Vs Babies

The fish are oviparous, they release unfertilized eggs and fertilize them outside their bodies generally in water. The Sharks either lay eggs or give birth to a fully developed young Shark. They fertilize the eggs inside their bodies and mother Sharks carry the egg and then give birth to the young.

8: Senses

fish have five senses as humans; Taste, Smell, Sight, Hearing, and Feeling. They also have an additional sense Lateral line, which enables them to sense vibrations in water. In Sharks, in addition to these senses, they have one more sense as well that helps them to be aware of their surroundings. Using these senses, they detect changes in water like the temperature and pressure. The Sharks have following seven senses:

i: Sight: They can see colors and exceptional details and some Sharks can even see in the dark.

ii: Smell: They have developed a smell sense and they have the ability to find the location from where the smell is coming.

iii: Sound: They can hear sound from miles away.

iv: Pressure Changes: The Sharks can detect the changes in water using the Lateral Line. This is the extension of the sense of hearing of Sharks.

v: Electroreception: The Sharks have gel-filled pores on their heads that detect the tiny’s electric field. They can even find the hidden fish in the sand.

vi: Touch: The nerve endings in the skin and teeth respond to the touch.

vii: Taste: They can taste the food.

9: Swim Bladder Or Liver

The fish have swim bladders filled with air that make them buoyant. This enables the fish to float in water even if they stop swimming. The Sharks lack swim bladders but they have oil-filled large livers. The liver helps the Sharks to easily swim. However, if the Sharks stop swimming they will sink. The only known exception to this rule is Spotted ragged-tooth Sharks as they can float in water like other fish.


Sharks are the oldest and most successful marine vertebrates. They are fish that are made up of cartilage instead of bones. This skeleton makes them more buoyant in water. Like other fish, they are cold-blooded, live in water, have fins, and breathe through gills. 

However, they have fusiform bodies with denticles on their bodies instead of streamlined bodies with scales. Depending on the species, Sharks either lay an egg or give birth to a fully developed individual. The fish has mostly six senses while they have seven senses.

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