the life of the dolphins is breathing with the lungs, while the class pisces breathe using the gills. This is why whales and dolphins have to swim to the surface to inhale oxygen because of the structure of the lungs that can not take oxygen from the water. It has been biologically proven that both deliver, not spawn. Nor is it ovovivipar like some fish species. Like humans, whales and dolphins multiply by childbirth.
photo taken by 
photo taken by
