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.
Today, the largest shark roaming the oceans is the huge whale shark. Unlike the megalodon, whale sharks are not predators. Instead, they're slow-swimming giants that eat mainly plants and plankton. Although not the size of the megalodon, whale sharks are still really big. They can grow to be over 40 feet long and weigh over 15 tons, which makes them the largest fish in the world.