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Fish vs. Whale: What's the Difference?

Edited by Janet White || By Harlon Moss || Published on December 5, 2023
"Fish are diverse, water-dwelling vertebrates with gills, usually with scales; whales are large marine mammals, part of the cetacean family, breathing air through lungs."

Key Differences

Fish are aquatic vertebrates that use gills to breathe underwater, possessing a variety of shapes and sizes. Whales, on the other hand, are large marine mammals that breathe air through lungs, showcasing significant size differences compared to fish.
The body structure of fish is adapted to their aquatic lifestyle, often covered in scales with fins for swimming. Whales, distinct from fish, have streamlined bodies with flippers and a tail fluke, adapting them for efficient movement in water.
Reproduction in fish varies widely, ranging from laying eggs to live-bearing, depending on the species. In contrast, whales give birth to live young and are known for their extensive care and nurturing of their calves.
Fish are cold-blooded, meaning their body temperature varies with their environment. Whales, however, are warm-blooded mammals, maintaining a constant body temperature regardless of the surrounding water.
The sensory systems of fish are often highly specialized for underwater life, including lateral lines for detecting movement and vibrations. Whales use sophisticated echolocation for navigation and hunting, a trait not found in fish.

Comparison Chart


Vertebrates with gills
Marine mammals with lungs

Body Temperature



Mostly egg-laying; some live-bearing
Live-bearing, nurturing young


Underwater through gills
Air-breathing through blowholes

Sensory Systems

Lateral lines, varied per species
Echolocation, highly developed hearing

Fish and Whale Definitions


Fish refers to the flesh of aquatic creatures, often consumed as food.
For dinner, we're having fish with lemon and herbs.


A large marine mammal with a streamlined body, part of the cetacean family.
The blue whale is the largest animal known to have ever existed.


To fish means to catch or attempt to catch fish, typically with a rod, line, and bait.
Every summer, we go to the lake to fish for bass.


'Whale' can refer to investing or gambling heavily and recklessly.
He's known to whale at the casino, betting large sums of money.


In poker, a 'fish' refers to an inexperienced or unskilled player.
He lost his money quickly, being a fish at the poker table.


A whale is also used metaphorically to describe something huge or immense.
That project was a whale of a task but we managed to complete it.


A cold-blooded vertebrate living in water, typically with gills.
The trout is a common type of fish found in freshwater streams.


In slang, 'to whale' means to hit or beat forcefully.
The baseball player whaled the ball out of the park.


'Fish out of water' describes someone feeling out of place or uncomfortable in a particular situation.
Without my phone, I feel like a fish out of water.


In finance, a 'whale' refers to an individual or entity holding a large amount of a particular cryptocurrency.
The market fluctuated dramatically after a whale sold a significant amount of Bitcoin.


Any of numerous cold-blooded aquatic vertebrates characteristically having fins, gills, and a streamlined body and including the bony fishes, such as catfishes and tunas, and the cartilaginous fishes, such as sharks and rays.


Any of various marine mammals of the order Cetacea; a cetacean.


Any of various jawless aquatic craniates, including the lampreys and hagfishes.


Any of various larger members of this order, including the blue whale, humpback whale, and right whale, in contrast to the porpoises and dolphins.


Do whales sleep?

Whales do sleep, but they remain conscious to breathe.

Do fish have good eyesight?

Fish eyesight varies; some have excellent vision while others don't.

What is the largest type of fish?

The whale shark is the largest fish species.

Can fish feel pain?

Studies suggest fish can experience pain.

How long can whales live?

Some whale species can live over 100 years.

Can whales communicate?

Yes, whales communicate using a range of sounds.

What's the smallest fish species?

The Paedocypris, a tiny freshwater fish, is among the smallest.

What do whales eat?

Whale diets vary; some eat fish, while others consume plankton.

Can all fish breathe underwater?

Yes, fish breathe underwater through gills.

Are all whales endangered?

Not all, but several whale species are endangered or vulnerable.

Do whales have teeth?

Some whales have teeth, while others have baleen plates.

Can whales hear underwater?

Whales have excellent underwater hearing.

Are fish cold-blooded?

Yes, fish are cold-blooded.

Do whales migrate?

Many whale species migrate long distances for feeding and breeding.

How fast can whales swim?

Speed varies by species; the orca can swim up to 34 mph.

How do fish breathe?

Fish breathe by passing water over their gills to extract oxygen.

How do fish reproduce?

Most fish lay eggs, but some give birth to live young.

How do whales sleep without drowning?

Whales sleep by shutting down one half of their brain at a time.

What's the most common fish?

Perch is among the most common freshwater fish.

Can fish live in both salt and fresh water?

Some fish species can live in both, but most are either saltwater or freshwater fish.
About Author
Written by
Harlon Moss
Harlon is a seasoned quality moderator and accomplished content writer for Difference Wiki. An alumnus of the prestigious University of California, he earned his degree in Computer Science. Leveraging his academic background, Harlon brings a meticulous and informed perspective to his work, ensuring content accuracy and excellence.
Edited by
Janet White
Janet White has been an esteemed writer and blogger for Difference Wiki. Holding a Master's degree in Science and Medical Journalism from the prestigious Boston University, she has consistently demonstrated her expertise and passion for her field. When she's not immersed in her work, Janet relishes her time exercising, delving into a good book, and cherishing moments with friends and family.

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