How the Whales does not have Fins like other fishes
The shape and structure of each living being on this earth will be different from one another and in the same way, there will be fins for some of the animals like the fish and so on and they will not be for the whales. Just as the gases in the air, there used to be different gases in the water that are in the diluted state. The water-based animals like the fishes and so on live with the water by taking the gases as their oxygen. The fins on their body are useful to separate these gases from the water and becoming useful for these animals. The whole process takes a lot of time and it is very difficult process.
The capacity of the oxygen that is to be taken by the fishes depends on the size of the fishes and for example, if the body of the fish is very big, the size of the fins will be such big and they used to work more effectively. As the fishes are the cold based body animals they need less oxygen for their body to survive. In addition, in contrary to them, the whales are the heat-based bodies and so they need the oxygen in large quantity for their survival. If this oxygen is to be get from the fins, they need big size fins to supply the oxygen to them. It is very easy to say but in practicality, it is very difficult to perform. On the other hand, the whales do not live with such a big fins on their body. That is the reason why the water living animals like the whales take the oxygen from their respiratory system but not with the fins.