What Is the Biggest Fish in the World?

The whale shark, weighing up to 47,000 pounds, eats only tiny plankton

Diver photographing a whale shark
Jones/Shimlock-Secret Sea Visions / Getty Images

The largest fish in the world might surprise you: It is the whale shark. At a maximum length of about 65 feet and weighing up to 47,000 pounds, a whale shark's size rivals that of large whales.

Largest Nonmammalian Vertebrate

The whale shark even sets the record as the largest living nonmammalian vertebrate on land or in the air or water. There are unconfirmed claims of individual whale sharks that are even larger and heavier—70 feet and weighing up to 75,000 pounds.

By comparison, school buses are generally no longer than 40 feet and generally weigh much less. Whale sharks live in tropical oceans and have very large mouths to filter the tiny plankton that is their only food. Their mouths can open up almost 5 feet wide, with over 300 rows housing about 27,000 teeth.

Whale Shark Facts

While its name may be deceiving, the whale shark is actually a shark (which is a cartilaginous fish). But these mammals are in no-way viscous man-eaters. "Despite their (second) name—shark—these giants are so gentle that snorkelers and scuba divers seek them out to swim alongside them," says The American Museum of Natural History. The museum also notes that the whale shark is listed as “vulnerable” on the International Union for Conservation of Nature Red List of Threatened Species due to threats from commercial fishing, "but the growth of whale-shark tourism may lead some communities to see them as more valuable alive."

Whale sharks have a beautiful coloration pattern on their back and sides. This is formed by light spots and stripes over a dark gray, blue or brown background. Scientists use these spots to identify individual sharks, which helps them learn more about the species as a whole. Indeed, every whale shark has a unique spot pattern, similar to a human fingerprint. The underside of a whale shark is light.

Scientists are not sure why whale sharks have this distinctive, complex coloration pattern. The whale shark evolved from bottom-dwelling carpet sharks that have noticeable body markings, so perhaps the shark's markings are simply evolutionary leftovers. Other theories are that the marks help camouflage the shark, help sharks recognize each other or, perhaps most interesting, are used as an adaptation to protect the shark from ultraviolet radiation. 

Other identification features include a streamlined body and broad, flat head. These sharks also have small eyes. Although their eyes are each about the size of a golf ball, this is small in comparison to the whale shark's massive size.

Distribution and Feeding

The whale shark is found in the pelagic zone in the Atlantic, Pacific, and Indian Oceans. Whale sharks are migratory animals that appear to move to feeding areas in conjunction with fish and coral spawning activity. 

Like basking sharks, whale sharks filter small organisms out of the water. Their prey includes plankton, crustaceans, tiny fish, and sometimes larger fish and squid. Basking sharks move water through their mouths by slowly swimming forward. The whale shark feeds by opening its mouth and sucking in water, which then passes through the gills. Organisms get trapped in small, tooth-like structures called dermal denticles, and in the pharynx. A whale shark can filter over 1,500 gallons of water an hour.

Whale sharks are also amazing swimmers, often moving over 10,000 km each year, and they can dive to around 2,000 meters in depth.

Other Large Fish

Basking shark (Cetorhinus maximus), underwater view, Baltimore, Cork, Ireland
Basking Shark. George Karbus Photography/Getty Images 

The second-largest fish is the basking shark, which grows to about 26 feet, but the largest ever accurately measured was 40.3 feet long and weighed over 20,000 pounds. It was caught in 1851 before fishing reduced the population and lifespan so that basking sharks this large are no longer seen. It also is a plankton filter feeder with a very large mouth. It is a commercially harvested fish for food, shark fin, animal feed, and shark liver oil. The basking shark lives in temperate rather than tropical waters, and it is often seen close to land.

The other type of large fish is a bony fish. The largest bony fish is the ocean sunfish, growing as large as 10 feet across its body, 14 feet across its fins, and weighing over 5,000 pounds. These fish eat mostly jellyfish and have a beak-like mouth.

Their size is rivaled by the largest freshwater bony fish, the beluga sturgeon, which is a prized source of caviar. While beluga were once recorded as being as long as 24 feet, with increased fishing they now generally grow to no more than 11 feet long.