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What are the differences between fish, sharks and whales?
Have you ever had questions like, ‘are sharks considered a mammal or a fish?’Or maybe, ‘is
a whale a shark or a fish?’ Well in this eBook we are going to go over what makes fishes,
sharks and whales so different from each other but yet still live in the same oceans.
Although all these animals (fishes, sharks and whales) live and thrive in the ocean, whales are
not sharks nor fish, but mammals and sharks are not mammals but yes they are fish but a
special species of fish. So let’s look into the major differences between these three marine
animals:
1) What is their body/skeleton made up of?

Sharks
Cartilage is what the shark’s body made up of. Cartilage is flexible, durable and has about half
the amount of density as bones. As a result this helps to reduce the skeleton’s weight and
conserves energy. Sharks also lack a rib cage which would result in its own weight crushing it
if it were placed on land
Shark cartilage

Fish
Bony fishes are divided into two groups, the ray-finned fishes and the lobe-finned fishes.
Since the ray-finned fishes include the vast majority of bony fish species, when you would refer
to bony fishes, you're largely talking about ray-finned fishes. But it's important to remember
that bony fishes include a handful of species of lobe-finned fishes as well. The skeleton of a
bony fish gives structure, provides protection, assists in leverage, and (along with the spleen
and the kidney) is a site of red blood cell production.

Whales
Whales have bones; the skeleton of a whale consists of a skull, a backbone, a rib cage, and a
collection of bones that form part of the flipper, but correspond closely to the bones in the
human arm and hand.
Whale's vertebrae
2) Buoyancy, how do they stay afloat?

Sharks
Sharks have specially developed livers that are less dense than most animals and contain a
large amount of oil, called Squalene oil. This makes it easier for them swim and makes them
faster than other fish.
Shark's liver

Fish
Fish generally have something called a swim bladder that is filled with air/gas and makes
them buoyant so that they float in the water even if they stop swimming.
Fish's swim bladder

Whales
Whales huge bodies are made up of a type of fat called blubber. This is what makes them
float. Seals, penguins and walrus also have blubber, but to a much lesser degree.
Whale cross section
3) Body shape

Shark
Sharks have a more rigid, torpedo-like, stream line body structure. A shark’s head is
generally more triangular in appearance and they also have very well developed pectoral fins.

Fish
A fish’s body is often fusiform, a streamlined body plan often found in fast-moving fish,
however, you also get filiform (eel-shaped) or vermiform (worm-shaped), these are the
shapes that usually occurs with bony fish. Normally, fish have slightly oval shaped heads, and
their pectorals fins would be less developed than those of a shark.
Different bony fish shapes

Whales
Whale’s body shape is also fusiform and the modified forelimbs, or fins, are paddle-shaped.
The end of the tail is composed of two flukes, which propel the animal by vertical movement,
as opposed to the horizontal movement of a fish tail.
Different whale shapes
4) Texture of skin

Shark
Fish and sharks do not have ‘skin’ like we generally think of skin. A shark’s skin is covered
with something called derma denticals, direct translation meaning’ skin teeth’. This derma
denticals are composed of material similar to their teeth, and acts as an ‘armor vest’ to
protects them from serious injury. Their skin is very ruff when you run your hand across it in
the opposite direction in which it swims, but smooth when you rub it from head to tail. This
allows the shark to move quickly and silently through the water.
Derma denticles

Fish
Like most of us know fish have scales, along with reptiles, because scales help protect a fish's
body and make it comfortable for the fish to swim and move from side to side. In addition,
scales help to protect the fish from predators especially if they are hard, sturdy, and slippery.
Fish scales

Whales
Whales have skin because they are mammals just like us. Some whales also have body hair
which scientist believe serves as a sensory structure, and may be used in social or sexual
situations, or for calves communicating a need to nurse. They also nurse their young with milk
they produce from their mammary glands.
Barnacles growing on the skin of a whale
5) How do they breathe?

Sharks
Sharks have 5-7 gills without a gill cover (operculum). Sharks can breathe in two ways.
Some sharks, mostly benthic sharks (bottom dwelling), do not need to move in order to
breathe. They have a special respiratory organ called a spiracle, located behind the eye, to
help them to pump water while remaining still. Other sharks, mostly pelagic sharks (relating to
open sea sharks), need to move in order to breathe - thus they rely on a process known as
ram ventilation. Basically, this means the forward motion of the shark sends water into the
mouth and forces it out through the gill slits.
Ram ventilation

Fish
Most fish have gills that they pump water through to take in oxygen and dispose of CO2. They
do this whether in motion or sitting still as they have everything they need to pump water
through their system. Most fish only have one gill slit but then multiple gills inside, the gills are
behind and protected by the operculum.

Whales
Whales are mammals, and mammals are the group of animals that breathe air using lungs.
So whales would come to the surface ever so often to breathe air into their lungs. Because
whales do not have noses like we do, instead they have a hole, called a ‘blowhole’, on top of
their head, so through this blowhole they breathe in and exhale.
Whale exhaling through blowhole
6) Reproduction

Sharks
Shark can reproduce in 3 ways depending on the species. There is viviparity (live-bearing)
just like humans give birth, e.g. Bull shark. Then, oviparity ( egglaying), which occurs mainly
in bottom dwelling sharks e.g. pajama shark, leopard catshark.
Then, there is Oviviparity(which is n mixture of the two above). Eggs develop inside the
female and then the offspring goes out, this is also the most common way that sharks give
birth, e.g. Ragged-tooth shark. Some sharks fertilize their eggs internally, while others fertilize
it externally.
Oviviparity
Viviparity
Oviparity

Fish
Fish also breed in different ways. There are two main strategies that fish use: Oviparity
(egglaying and vivparity - live-bearing). Live-bearing female fish are internally fertilized by the
male fish, and carry the fry for about a month before delivering them. Egglaying fish lay eggs
instead of giving birth to little fish. However egg-layers have many methods of laying eggs. For
example, substrate spawners which lay their eggs in protected areas such as plants, rocks,
wood. And then mouth-brooders that actually keep their eggs in their mouths until the eggs
hatch out.
Mouthbrooder releasing young

Whales
All whales give live birth (viviparity), because whales are mammals. The calves grow inside
their mothers and are born with their fins emerging first. The offspring are born during the
migration process in most instances. Females often have many partners during the mating
season so it is highly likely that she will conceive. Since the female will only have one baby
and then nurse it for a full year, so the rate of reproduction is less than fishes and sharks.
Mother and baby humpback whales
Conclusion
Although each of these fascinating marine animals are different from one another, we can really
appreciated their uniqueness and amazing ability to adapt in the great oceans of the world.
Differences between fish, shark and whales. Comprehension test
1) Name the six major differences between fishes, sharks and whales discussed in the ebook
2) Whales and fish have bones while sharks have?
3) What makes sharks and fish float?
4) What is the name of the body type that whales have?
5) How many gills does a shark have?
6) What is the name of the opening that whales use to breathe air on the surface?
7) Name the 3 ways in which sharks reproduce?
8) True or False: Fish only lay eggs
9) Fill in the blanks: All whales give live birth (viviparity), because whales are _________
10) Sharks are covered with skin called derma denticals, what does that mean?