Many readers will think that dolphins are fish, because they live in the water with fish, and their body organs and structures are similar to each other. For example, their body shape, dolphins do not have limbs, their body shape is similar to fish. However, these characteristics are only the structures that dolphins evolved in the process of evolution to adapt to the environment in the water, and these structures can not change their original attributes.
Dolphins are not fish themselves, and some of their key characteristics are different from those of fish. For example, their reproductive methods are very different from those of fish. Most fish reproduce by laying eggs, but dolphins do not. Moreover, dolphins and fish breathe differently. Fish have specialized breathing parts. They breathe with their gills, but dolphins do not. Therefore, dolphins should not be mistaken for fish.
As mentioned above, dolphins are quite different from fish, and they cannot be considered fish. Dolphins are essentially mammals, and they are a typical mammal. Some of their features are unique to mammals. For example, the two characteristics described above, dolphins do not use oviparous way of reproduction, but use viviparous way of reproduction, and they also have lactation period, which shows that they are obviously mammals; Dolphins don't breathe with their gills, they breathe with their lungs. In addition to these two characteristics, there are some other characteristics that conform to the characteristics of mammals. Dolphins are warm-blooded animals, which is what most mammals have.
