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.
The Blue Whale. At up to 33.58 meters (110 ft 2 in) in length and 172 metric tons (190 short tons) or more in weight, it is the largest animal ever known to have existed. What makes the Blue Whale a predator is that, as with other baleen whales, its diet consists almost exclusively of small crustaceans known as krill. The whales always feed on large amounts of krill, sometimes eating up to 3,600 kilograms (7,900 lb) of krill in a single day.