One of the biggest differences between whales and fish is that whales need to breathe air. They have lungs, and they need to come to the surface of the water often for air. Their blowhole is like their nose, which is on top of their heads. It is located on the top of their head so that the whale can breathe fresh air without coming very far out of the water. Before a whale dives under the water, they will take several deep breathes - just like you would do before diving under the water.
Whales also swim very differently than fish.
A fish swims by moving its tail from side to side, but a whale moves it s tail up and down to propel itself through the water. Whales are covered with skin which is very smooth and firm. It kind of feels like soft rubber to the touch. Whales also give birth to live babies, they do not lay eggs like fish. You may wonder how a baby whale is born underwater if it has to breathe to live.