• Question: Why are animals like sharks classed as fish but then whales are classed as mammals?

    Asked by lovetolife to Damien, Rachael, Simon, Suzi, Tim on 16 Jun 2011.
    • Photo: Suzi Gage

      Suzi Gage answered on 14 Jun 2011:

      Hi @lovetolife
      Thanks for this question. It’s all about how the animals eat, and reproduce, which determines whether they are fishes or mammals. Although sharks and whales look quite similar from the outside, on the inside they are very different. Sharks actually lay eggs, so they are fishes. Whereas whales reproduce like humans, they give birth to live babies. There are lots of other differences too. They have very different looking skeletons as well.

      Hope this answers your question 🙂

    • Photo: Damien Hall

      Damien Hall answered on 16 Jun 2011:

      This has to do with the way that these animals breathe. Sharks are fish because they breathe through their gills (flaps of skin that keep water out of their bodies), but whales are mammals because they have to breathe air (and for other reasons too). That’s why you see whales coming to the surface (it’s called breaching) and blowing air and water out of their blowholes – they need to fill their lungs and dive again. But they have really big lungs, so they can stay underwater for a really long time! You should check this with your biology or science teacher, though.

      But here’s an interesting thing I learned recently: from a certain point of view, there’s no such thing as a fish. What the person who said that meant was that there are very few similarities that all of the animals that swim in water and breathe through gills all share – apart from swimming and having gills. So, this person said, calling all of them “fish” is like calling everything that lives on land and breathes air a “monkey”. I thought that was really interesting!

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