Marine Mammal vs Fish
Critter File
Posted: August 30, 2017


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It’s a shark and whale showdown! But it’s also a fish and marine mammal showdown. (Marine mammals include species like whales, dolphins, seals, and walruses—non-fish creatures that rely on the ocean for food and a place to live.) God gave both mammals and fish some incredible features!

Hair: Fish don’t have fur. Marine mammals do—though usually not much. Some whales have fine hair, especially on their head. Whale babies have a small amount of fur before they are born.

Breathing: Just like you, whales and other marine mammals take air into lungs. Some use blowholes at the tops of their heads. Fish extract oxygen from water using their gills.

Blood: When water gets cold, mammals need to keep warm. A mammal’s warm blood does that job. A thick layer of blubber insulates the mammal too. But fish are cold-blooded. When the water is cold, a fish’s blood and body are cold too. Brrr!

Birth: Marine mammals are born alive. Fish hatch from teeny, tiny globs—fish eggs.

Young: Most baby marine mammals are taken care of, protected, and fed milk by their mothers for several months. Some fish build nests and guard their young, but most do not care for their young at all. They hatch and live on their own immediately. That’s no surprise. Most fish lay hundreds or thousands of eggs each year! That’s way too many to pack lunches for and take to violin lessons!

Swim: To move through the water, many marine mammals use their tails and flukes to move up and down. When fish swim, their spines and tail fins move from side to side.

Limbs: Have you ever seen a fish with arms and legs? Neither have we. But a mammal’s flippers can work a little like arms or hands. The bones of an orca flipper even look like finger bones. Did you know that polar bears are counted as marine mammals too? They doggy paddle through cold water with their webbed feet!