References and Further Information: 1  Morrissey, J.F. and J.L. Sumich. 2012. Introduction to the Biology of Marine Life (10th Edition). 2  University of California Museum of Paleontology. Bilateral (left/right) Symmetry.
A lot of things. For one, Whale sharks are fish and use gills to breathe. Blue whales are mammals. The blue whale is also bigger than the whale shark. The tail structure is also different if you watch the whale shark swim, it uses its tail in a side to side motion while the blue whale uses a up and down movement.
Whale sharks are fish, not mammals. According to an article by Jennifer Kennedy on About.com, the whale sharks are the largest fish in the world. They grow as long as 65 feet and weigh up to 75,000 pounds. Female whale sharks are generally larger than males.