Question

Why whales are not grouped in the fishes?

Answer 1

There are wide differences between whales and fishes

Whales	Fishes
Mammals	Not mammals
Breath air with lungs	Breath air with gills
Warm blooded animals	Cold blooded animals
Have hair, have eyelids and tear ducts	Typically have scales, do not have hair, do not have eyelids or tear ducts
Have arm bones, hand bones, and finger bones, do not possess bony fins	Do not have arm bones, hand bones, or finger bones, typically have bony fins
Evolved from other land-dwelling mammals	Evolved from primitive aquatic pre-fish ancestors