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Whales are marine mammals, but many people often think they are fish. Although there are similarities, there are also many differences.

  1. Whales breathe oxygen from the air
  2. Whales give birth to live young
  3. Whales breastfeed their young
  4. Whales are warm-blooded
  5. Whales are born with a small amount of fur

Many people ask me why whales are mammals and not fish. In this article, I look at the differences between fish and whales and the five mammalian characteristics that whales share.

Whales often swim close to the shore. Find out why here


1. Whales Breathe Oxygen From The Air

Whales must use oxygen from the air to breathe. Whales have lungs, and their blowholes are repositioned on top of their heads to absorb oxygen easily. 

Baleen whales have two nostrils, whereas toothed whales only have one. Whales cannot breathe through their mouths as the trachea is not attached to it, so the blowholes on their heads are their only means of oxygen intake. This separation removes the risk of an airway opening when food is swallowed underwater.

Whales have developed an efficient respiratory system, where they can utilize 90% of the oxygen they breathe in, in contrast to the 15% humans use. 

Whales produce a protein called myoglobin, which allows them to store additional oxygen within their muscles for later use; this is particularly useful for long dives, with some whales staying underwater for hours. All mammals produce myoglobin, but whales can have much greater amounts than other animals.

Due to living in an aquatic environment but needing to breathe air, whales never fully sleep. They can sleep with one half of their brain while the other stays awake and alert in case they need to breathe or are at risk of attack from predators.

Whales Give Birth To Live Young

Whales give live birth to calves after an extended gestation period, which lasts between 10 and 17 months, depending on the species.

During this time, the calf is connected internally to the mother by an umbilical cord. They share blood, which provides the calf with the nutrients it requires and removes waste products using their internal organs.

Calves are born underwater. While young mammals are usually born headfirst and take their first breath as soon as air touches their faces, marine mammals, including whales, give birth with the tail coming out first. 

This method ensures that the calf will not drown if the birth takes longer or there are complications. As whale calves are born ready to swim, being carried tail first means facing the same direction as the mother.

If you want to know more about how whales breastfeed underwater, I have written this article.

3. Whales Breastfeed Their Young

Whales do not breastfeed their young in the same way that land mammals do. Instead, they nurse their calves through mammary glands. Female whales have mammary glands that produce milk, and they typically nurse their calves by secreting this milk into their mammary ducts. The calves then suckle on the teats or nipples found in the mother’s mammary area to consume the milk.

The mother will continue nursing anywhere between six months and two years, depending on the species, until the calf feeds independently. Whales’ mouths are not flexible enough to latch on, so the mother whale has to eject the milk into the calf’s mouth. However, the calf can curl its tongue so that the milk is directed into its mouth and not wasted.

Once the calf is born, the mother produces milk in a thick paste form with high-fat content, which reduces the risk of the milk dissolving in the water. 

4. Whales Are Warm-blooded

Whales are warm-blooded mammals, also known as endothermic homeotherms. Whales must maintain their body temperature using energy they convert from food, rather than their surroundings.

Cold-blooded fish, including sharks, are ectothermic, meaning they use their outside temperature to regulate their body temperature.

As whales are so large, there has been some discussion about how whales can take in enough food to produce the required energy to keep them warm. Baleen whales use large keratin plates in their mouths to ensure that they eat enough food to provide this.

Baleen plates allow whales to hunt for smaller prey much more efficiently by taking in large amounts of water and filtering water from their mouth through the baleen plates, leaving the small organisms behind. 

Smaller, toothed whales tend to eat larger octopus and, in many cases, seals, which have a high-fat content due to their thick layer of fat.

The blubber built up from eating fatty food assists not only with insulation but also as a food store if they cannot find food for an extended period. The blubber aids migration as whales build their fat store for traveling between feeding and mating grounds.

Whales can endure water temperatures as low as -2 Celsius or 28.4 degrees Fahrenheit and air temperatures of -40 degrees Celsius or Fahrenheit. Due to movement and salinity levels, seawater does not freeze at these frigid temperatures. 

Whales maintain their internal body temperatures through both physiological and behavioral methods. Behaviorally, whales will migrate if they are too cold and often migrate to mate and look after their calves in warmer waters. 

Because whales are large, they preserve heat through a large surface area to volume ratio. This means that there is a low amount of skin compared to their weight to lose heat. 

5. Whales Have Fur

One of the more subtle features of whales is that they have fur at some point in their life cycle.

This does not necessarily mean that whales are visibly hairy or that the adults of mammalian species have visible hair.

Humpback whales have bumps that can be seen on their backs. These bumps are hair follicles that can be either active or inactive, depending on the individual. This leads to some whales having more hair than others.

Hair can be seen on most newborn whales and other marine mammals, but the majority of them shed the hair within the first few weeks of life after birth.

Hair is not necessary for whales like many other mammals, such as dogs or cats. Most mammals use their fur to keep warm, but whales use a layer of fat called blubber to regulate their temperature.  

Most dolphins are also born with hairs around their muzzles, which are then lost soon after birth, except the Amazon Dolphin, which uses whiskers as sensory organs.

Whales have excellent senses. Find out more here.

What Is A Mammal?

A mammal is a warm-blooded animal born with fur that feeds milk to its young. They also have lungs and, therefore, must breathe air. When thinking of a mammal, the prominent examples are humans, dogs, and cats. 

Marine animals such as dolphins, whales, dugongs, and manatees are also considered mammals as they possess all the typical mammal traits.

The order of Mammalia includes animals that possess mammary glands. The order incorporates Monotremes (egg-laying mammals), such as echidnas, and Marsupials (mammals with pouches), including kangaroos and possums. The third includes Eutherians, which are also known as placental mammals. Whales are Eutherians and have a long gestation period, as evidenced by blue whales carrying their young for 10-12 months.

Why Are Whales Not Fish?

Whales are not classed as fish as they don’t share the same characteristics. Fish use gills for respiration, while whales use lungs and breathe in oxygen from the air, not water. Whales are warm-blooded (endothermic), while fish are cold-blooded (ectothermic) and cannot regulate their body temperature.

Fish and whales do share some characteristics. Both have vertebrae and live in water, but the differences see them being classified in two different Orders.

Why Are Whales Not Sharks?

All cetaceans, including whales and dolphins, are mammals, while sharks are fish. Sharks are ectothermic (cold-blooded), while whales can control their body temperature (warm-blooded.)

Sharks use gills to extract oxygen from the water, while whales use their lungs to take in oxygen from the air. The main similarities between whales and sharks are that they are both large marine animals and some sharks give birth to live young.

Are All Cetaceans Mammals?

Cetaceans are an order of marine mammals that incorporates about 90 species, including 49 species of river and oceanic dolphins and porpoises. The other 41 species are divided into 14 species of baleen whales and 27 species of toothed whales. These carry the mammalian traits of being warm-blooded, having fur, lactating, and breathing air. All cetaceans are mammals.

Cetaceans belong to the eutherians group as they do not lay eggs or possess pouches and give birth to live young after an extended gestational period. They then continue parental care with lactation, like land mammals, until their young are independent.

Did you know that whales migrate? Please find out more in this article I wrote.


Similarities to Land Mammals

Even after millions of years in the sea, whales still have the same bone structures as land mammals. When studying the whale’s bone structure, it is possible to see that their pectoral fins contain the same bones that would be recognized as hands and finger bones in humans or foot and digit bones in a hippopotamus, their closest living relative.

A whale’s tail is an altered version of the tail of land mammals, and vestigial rear limbs can still be seen. The connection with the hippopotamus, a semi-aquatic mammal, was discovered through the similar structure of the ankle bones of hippopotami and whales.

Although sparse, whales have thick bristly hairs on their bodies and have continued to breathe air, with the nostrils migrating to the top of the head and repurposed as a blowhole that can blow air and water to heights of 30 feet or 10 meters.

If you are going on a whale-watching trip, it is best to be prepared.  Find out more in this article.

References And Further Reading

Spying on whales: The past, present, and future

Whales, dolphins, and porpoises 

Whales, dolphins, and seals:  A field guide 

Guide to whale watching in North America

The illustrated encyclopedia of whales and dolphins

Hickman, C., Roberts, L., Keen, S., Eisenhour, D., LarsonI’Anson’Anson, H. 2014, Integrated Principles of Zoology, McGraw Hill Education, New York

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Stone, M. 2019, How Much Is A Whale Worth? National Geographic Partners, Retrieved 01/02/20, <>

Whale and Dolphin Conservation, Facts About Whales, Whale and Dolphin Conservation, retrieved 01/02/20, <>

Whale and Dolphin Conservation, Do Whales and Dolphins Have Hair?, Whale and Dolphin Conservation, retrieved 01/02/20, <>

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Garrod, B. 2020, How Do Whales Breastfeed Underwater?, Discover Wildlife, retrieved 01/02/20, <>

USCB Scienceline 2015, How Can Whales Hold Their Breath Longer Than Most Mammals? National Science Foundation & USCB School-University Partnership, retrieved 1/2/20, <>

Whale Facts 2020, How Do Whales Breathe?,, retrieved 1/2/20, <>