To solve this question, the user needs to have knowledge of marine biology.
Now, let's go through each option and explain why it is right or wrong:
A. Killer Whale: Killer whales are not fish. They are actually the largest member of the dolphin family.
B. Great White Shark: Great white sharks are also not the largest fish in the world. They are one of the most well-known shark species but are not the largest.
C. Blue Whale: Blue whales are the largest animals on earth but they are not fish. They are mammals.
D. Whale Shark: This option is correct. Whale sharks are the largest fish in the world, growing up to 40 feet (12 meters) in length and weighing up to 47,000 pounds (21,500 kg). They are filter feeders and feed mainly on plankton.