A fish is essentially a cold-blooded vertebrate which is characterized by a slender body, heart with two chambers, gills, fins and scales. Unlike marine animals a fish doesn’t have to reach the surface of water to breathe but does so with feather tissue membranes referred to as gills. A fish breathes in water with gills which extract oxygen from the surrounding water.
However, dolphins and whales are mammals as they breathe in air using lungs and they give birth to their young ones and also feed their young ones. Their nature to take in oxygen from the air also gives them a distinguished identity from fish. Mammals have noses in the middle of their heads, also called as blow holes, which shut down when whales and dolphins are in the water and, otherwise, open up to take in fresh air to breathe which is high in oxygen.
