Is the biggest animal really a fish

Mr. Big lives in the deep ocean for, like a fish, he cannot live on the land. Most of his time is spent with the fishes deep below the waves. But Mr. Big is not a fish and the reasons why he must live in the sea are very different from the reasons why a fish must live in the sea,
A fish has gills for taking his oxygen from the water. He suffocates in the air. The worlds biggest animal has lungs, Just as we do, for taking oxygen from the air. Though he lives in the sea, he must come up to breathe two or three times every hour. A fish is covered with scales and the huge body of Mr. Big is covered with lots, of skin, plus a few bristly hairs, A fish hatches from a glassy egg, but Mrs. Big gives birth to a chubby baby and feeds him on mother’s milk,
This last item proves that the world's biggest animal is a mammal, for only the mammals feed their babies on mother's milk. Most of the warm blooded, fur coated, air breathing mammals live on the land. But ages ago, certain mammals took to living in the sea where food was very plentiful. Their descendants gave up the skills for coping with land life and developed water skills. They are the seals, the dolphins and the giant whales,
Water gives more support to a big body than does the air, The whales made the best of this fact and grew bigger and bigger through the ages. Now they are so big that their huge bodies collapse when they come cut of the water. When a whale is washed up on a beach, his lungs and bones are crushed under the weight of his tremendous body. He must stay in the ocean,
The biggest of the many whales is the blue whale. His body may be 100 feet long and in order to carry him we should need several flat freight cars. We would need a whale of a pair of scales to weigh him, On one side of the scales we could put 300 average human families, plus 200 cows, 500 dogs and cats, 2,000 mice, several thousands birds and several billion insects. In fact, we could put the entire human and animal population of a small village.
On the other side of the scales would be one blue baleen whale, weighing about 150 tons. Our giant would most likely be Mrs. Blue Whale, for as a rule she is slightly bigger than her husband. Not only is she the biggest animal alive, she is the biggest animal who has ever lived in the world. The modern whales are bigger than the great dinosaurs that once lived on the land.
For his size, the big whale is not a tremendous eater. He may be as bulky as a dozen elephants, each needing a quarter ton of food a day. The whale eats only about a ton of food each day and his diet is plankton, a seafood mixture of seaweed and small sea dwellers no bigger than shrimps.