The Whale Shark (Rhincodon typus) and the Basking Shark (Cetorhinus maximus) are the two largest fish species in the world’s oceans. Both are massive, slow-moving filter feeders that pose no threat to humans, but they represent distinct lineages of shark evolution. Their impressive size often leads to confusion about which one holds the title of the largest fish. This comparison explores the definitive size difference and the unique biological traits that separate these two oceanic giants.
The Definitive Size Comparison
The Whale Shark is definitively the larger species, holding the record as the largest fish in the world. The largest reliably measured individual reached 18.8 meters (about 62 feet) and weighed up to 34 metric tons (75,000 pounds). The Basking Shark is the second-largest fish, but it is noticeably smaller. The largest accurately measured Basking Shark was about 12.27 meters (40.2 feet) long, weighing around 16 metric tons (35,000 pounds). While adult Whale Sharks commonly attain lengths between 12 and 14 meters, Basking Sharks are more typically found in the 7 to 9-meter range.
Characteristics of the Whale Shark
The Whale Shark’s distinct anatomy is suited to its life in warm, tropical waters. Its head is broad and flattened, featuring a massive, transverse mouth positioned at the front of its snout, a rare feature among sharks. This terminal mouth allows it to actively scoop and gulp water while feeding, a method known as active suction feeding. Its coloration is a dark gray or brownish skin marked with a unique “checkerboard” pattern of pale spots and stripes. This spotted pattern is unique to each individual, allowing scientists to use photo-identification to track them.
Characteristics of the Basking Shark
The Basking Shark is adapted to cooler, temperate and boreal waters, utilizing a different filter-feeding technique. Its mouth is sub-terminal, positioned slightly underneath the conical snout, and is proportionally larger than the Whale Shark’s, capable of opening over a meter wide. It is an obligate ram filter feeder, relying solely on swimming forward to force water over its massive, bristle-like gill rakers. A defining visual trait is the five pairs of enormous gill slits that nearly encircle the entire head. Its coloration is typically a mottled gray-brown to slate-gray, lacking the distinct spot pattern of the Whale Shark.
Conservation Status and Global Distribution
Despite their immense size, both the Whale Shark and the Basking Shark face serious conservation challenges due to their slow growth and reproductive rates. Both species are currently listed as Endangered on the IUCN Red List of Threatened Species. The Whale Shark prefers tropical and warm temperate seas, but its Indo-Pacific population has declined significantly due to targeted fishing and bycatch in commercial fisheries. The Basking Shark is found in amphitemperate waters (northern and southern temperate oceans). It was historically targeted for its valuable liver oil and fins, and continues to suffer from accidental entanglement in fishing gear and vessel strikes, especially when feeding near the surface.