Whales live in the water like fish, and can not leave the water for too long, and their body structure is very similar to fish, so many people will think that whales are also fish. That's a mistake. A whale is not a fish, it's a mammal. There are several characteristics that determine that a whale is not a fish:
1. Breathing: As a mammal, whales use lungs to breathe, so they cannot breathe in the water, but need to periodically come to the surface to breathe before entering the water. But fish breathe with gills and can breathe freely in the water.
2. Reproductive methods: The reproductive methods of whales are also very different from those of fish. They reproduce by viviparity. Their pregnancy time is even longer than that of humans. Fish generally use oviparous way of reproduction.
3. Need to suckle: As a mammal, another important characteristic of whales is different from that of fish, that is, whales need to suckle, that is, young whales need to supplement nutrition through milk. Fish is different, fish eggs themselves contain relatively rich nutrients, small fish rely on the nutrition can maintain life.
The differences between whales and fish have been introduced above. Although they are mammals, they can still live in water. This is because in the process of evolution, in order to adapt to the living environment in the water, whales have evolved some body structures suitable for living in the water. For example, in order to cope with the resistance in the water, whales have gradually formed streamlined bodies, just like fish. This phenomenon is a typical example of convergent evolution.
