Are Whales Just Really Big Fish?

humpback whale with mist out of blowhole

Written by Cindy Rasmussen

Published: November 28, 2021

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If you ask a Kindergarten class where do fish live they may shout, “In water!” Fish can live in lakes, rivers, the ocean and even in a little bowl on your kitchen table. Whales live in water just like fish, but are whales fish? Let’s take a look at the similarities and difference of whales and fish.

Where do whales and fish live?

Animals With the Toughest Skin-sperm whale

A sperm whale in the Indian Ocean. Both whales and fish live in aquatic environments

This is one thing whales and fish have in common, they both live in an aquatic environment. Depending on the species fish can live in freshwater or salt water. Whales primarily live in the ocean but there are a few dolphin species (yes, dolphins are a kind of whale) that live in fresh water like the Amazon River dolphin. Some animals like alligator and crocodiles live in water and on the land whereas both whales and fish are completely aquatic.

How do whales and fish breathe?

Animals That Live in Coral Reefs: Whale Sharks

Whale sharks are filter feeders and can neither bite nor chew. They can process more than 6,000 liters of water an hour through their gills.

One of the biggest differences between whales and fish are that whales are mammals so they breathe air and have lungs. Whales must come to the surface of the water to get air through their blowhole (some have one, others have two). Their blowholes are connected to their lungs and provide it with the needed oxygen. Large whales have large lungs so they can stay under water for extended periods of time. Sperm whales can hold their breath for up to 90 minutes!

Fish have gills. Gills are slats on the side of the fish that allow water to flow through it. Tiny blood vessels are able to extract the oxygen from the water and eliminate the carbon dioxide. Some fish can extract enough oxygen out of the water without having to swim around much whereas some sharks (sharks are fish, not whales) have to keep moving so that the water passes over their gills. Other sharks have a buccal pump system that actively sucks water into their mouths across the gills so they do not have to constantly be moving.

Fish vs. whale: How big are they?

Are Blue Whales Endangered - A Blue Whale Near the Surface

Blue whales can grow to be more than 100 feet in extreme cases

Whales are the largest animal on the planet, but there are some fish that get pretty big too. The largest whale is the blue whale which can get to be 70-90 feet long (and the largest ever measured more than 110 feet)! Followed by the fin whale, right whale, sperm whale and humpback. The biggest fish species actually has the word “whale” in its name, the whale shark, but it is a shark (and sharks are fish). Whale sharks can grow to be more than 50 feet long. The other largest fish are also sharks with the basking shark, great white shark and tiger shark coming in next. The biggest ray (which is a fish) is the Giant oceanic manta ray and the biggest bony fish (Osteichthyes) is the ocean sunfish. These sunfish are very strange looking fish with no tail and blob-like shape. It floats on its side near the surface of the ocean. They can get to be 14 feet from fin tip to fin tip and weigh up to 5000 lbs! For reference a Smart Car weighs around 1550 lbs, and an adult rhino can weigh 5000lbs. Now that is a big fish!

How do they swim?

Another difference between whales and fish is their tales, whale’s tails have a fin that is horizontal and it moves it up and down to mover through the water. Fish tails are vertical and are moved back and forth to glide through the water. Some fish, like rays don’t use their tail for propulsion but flap their sides to create a current to scoot along.

How do fish and whales maintain their temperature?

Do Whales Have Hair - Humpback Whale Hair

Whales are mammals and therefore are warm blooded. To maintain their temperature they have a thick coat of blubber. You can tell by looking at whales that they are covered in blubber but what about the sleek dolphin, do they have blubber? Yes! They have a layer of blubber under their skin that serves the same purpose of maintaining warmth.

Fish are not mammals and are cold blooded so they do not need to retain warmth in the chilly depths of the waters they live in. They can adapt to the temperature of their surroundings. In the animal world it seems there are always exceptions so there are some tuna and sharks that are partially warm blooded, but in 2015 scientists found the first fully warm blooded fish. The opal fish which is a large round fish that shimmers in the sun can be found off the coast of Hawaii. Scientists tested the core temperature of opal fish and found it was consistently warm because heat was circulated throughout their whole body!

How do they whales and fish have babies?

mother and baby humpback whale swimming together

mother and baby humpback whale swimming together

Going back to whales being mammals, one characteristic of mammals is that they give birth to live young. Talk about big babies! A baby blue whale can weigh 5,000-6,000 lbs! That is about the same size as the adult rhino mentioned above. Whales typically give birth to one baby at a time, with an occasional instance of twins.

Fish on the other hand lay eggs, and lots of them! Some fish species can lay over a thousand eggs at once. There are a variety of ways that fish lay eggs, the most common is that the females release the eggs into the water or near rocks and crevices and the male comes along and fertilizes them. They grow into larvae and hatch and then go on to mature into adult fish. Some fish have the eggs grow inside their bodies and then release live larvae.

Sharks are a little trickier, there are some that lay eggs (oviparous) and there are others that give birth to live baby sharks (viviparous). Sharks do not have thousands of eggs but they do have more babies at once than whales. The sand tiger shark gives birth to two babies whereas the blue shark can give birth to more than a hundred live shark babies at once, now that is a lot of brothers and sisters!

So, are whales fish?

Whales are not fish. As we’ve described, whales are warm-blooded while almost all fish are cold-blooded. Fish also breath through gills while whales have lungs and breath air from above the ocean’s surface. In addition whales give brith to live young while most fish lay eggs. For all these reasons, whales are mammals that evolved from land creates about 50 million years ago while fish have always been adapted for the seas.

How do whales and fish raise their young?

Baby Whale Shark - Juvenile Swimming the Ocean

A junveile whale shark swimming on its own

Another difference between whales and fish is that whales typically raise their young and nurture them until they are able to take care of themselves. Being mammals, newborn whales rely on their mothers to provide milk which strengthens their bond. Some whales stay with their mothers for 6 months to a couple of years.

Fish in general are on their own when they hatch. Many species are born with a sack of nutrients that they live off until they are adept at finding their own food. Shark babies that are born from eggs are typically on their own and equipped to survive once hatched. Sharks that give birth to live babies, like the hammerhead shark try to find a good place to give birth so that the babies can find food and shelter, but they are born ready to venture out on their own.

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About the Author

I'm a Wildlife Conservation Author and Journalist, raising awareness about conservation by teaching others about the amazing animals we share the planet with. I graduated from the University of Minnesota-Morris with a degree in Elementary Education and I am a former teacher. When I am not writing I love going to my kids' soccer games, watching movies, taking on DIY projects and running with our giant Labradoodle "Tango".

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