why are whales not considered to be fish?

Where is a Marine organism that lives in water. It size resembles a fish but in reality it does not come in fish category. It is mammals.

Its growth is considered as glants zoo- dinosaurs. who distributed over earth million of year ago today. Blue whale or sulphur bottom whale is the most gargantuan organism. He breathes like us and its gills are not present.

In whose next part of the head is nostril and its nostril inside the water closes. This can be breath 5 -10 minutes uninhaled  by the female begent weaned and suckle her body parts meet mammals.

Some whales teeths and some have plate shaped bones instead of teeth. By all these qualities whales are considered as mammals