What is the biggest fish?

In this post, we will know The biggest fish species and also understand its general anatomy, biology, ecology, main threats and needs for conservation.

The biggest fish

The biggest fish in the world is the Whale Shark. Although the name has the word whale, it is not a mammal. This fish species belongs to the group of cartilaginous fish. Whale Sharks live in the marine environment, in tropic and warm temperate waters. With remarkable size and colour, the Whale Shark represents the largest species of fish in the world. Unlike most shark species, the whale shark is a filter feeder, feeding on plankton and small fish, such as anchovies and sardines. 

Whale Shark

The whale shark is not aggressive, on the contrary, it is very peaceful and gentle. It has the habit of living solitarily. However, sometimes it is possible to encounter groups of Whale Sharks in feeding grounds. They inhabit the tropical open and coastal marine waters. 


Extraordinary in size, Whale Sharks can reach up to 12 metres in length and weigh up to 12.5 tons. They also have a whale-like appearance, which inspired the common name of the species. The Whale Shark (Rhincodon typus) is characterized by a flattened head and a big mouth. The mouth opening can reach up to 1.5 metres, almost the entire width of its body. 

This fish has small eyes, behind which are the spiracles, and five-gill slits on each side of the head. Its unique colour is one of its most striking features: the back and sides vary between grey and dark blue tones, punctuated by light round spots, while the ventral region is predominantly white. The patterns observed for the spots even reveal the different individuals of a population, being used to identify these animals. 

The Whale Shark has around 300 small teeth in its mouth, with unknown function, and 10 pairs of filtering organs, which help during feeding behaviour. This fish also has a pair of dorsal fins (the first is larger than the second) and a pair of pectoral fins, in addition to a crescent-shaped caudal fin. 


The Whale Shark is distributed throughout the great oceans, inhabiting tropical and temperate regions, except for the Mediterranean Sea. This fish can be found in shallow and deep waters, especially on the coastline of countries such as Mexico, Australia, and the Philippines (as it prefers warmer waters). 

Usually solitary, the Whale Shark can be seen in groups of up to 100 individuals in the feeding areas. These feeding grounds are places with high concentrations of plankton. During the spring, these animals make long migrations to the coast of Australia for reproductive and feeding purposes. Extremely docile and intelligent, these fish pose no danger to humans.

R. typus is one of three filter shark species in the world. Unlike the other two, the Peregrine Shark (Cetorhinus maximus) and the Great mouth Shark (Megachasma pelagios), the Whale Shark filtration works with the sipping from the surface of the water to obtain the plankton, not needing to swim with his mouth open to feed similarly to the other two. 

Habitat and reproduction

Whale Sharks prefer to inhabit warm waters. Thus, they almost never abandon the tropics. They can be seen in the Yucatán Peninsula, islands of Honduras, Galapagos Islands, Philippines, Thailand, Western Australia, Caribbean, and Brazil. They were rarely observed off the coasts of Europe and in the region of South Africa. 

The largest distribution area of these animals is located around the Philippines, between January and May. Researchers claim that they are animals with migratory habits in search of food and during reproductive seasons.

The Whale Shark is considered an ovoviviparous animal, that is, fertilization is internal, with eggs being stored inside the female. Embryos hatch from the eggs still inside the mother’s body, where they complete their development. Embryos are fed through the yolk sac, where they remain attached until their birth. The type of reproduction that Whale Sharks have is also called lecithotrophic viviparity. 

Whale Sharks and tourism

Some regions have become the target of a lot of tourists exploitation due to the presence of the Whale Shark. In Western Australia, for example, in some regions, it is possible to swim together with this shark. The Whale Shak size and appearance can frighten some people. However, they are docile and do not pose threats to humans. 

Predatory hunting

The Whale Shark is a species considered to face the possibility of extinction in the short future. In some countries, such as Taiwan, predatory hunting of this animal is still allowed.

Whale Shark is a species highly valued by the international market, The demand for meat, fins (used in the production of aphrodisiac and medicinal soups), and oil from Whale Sharks represent one of the main threats to the conservation of these animals, together with unregulated fishing.

This species is also a victim of bycatch – accidental capture by fishing vessels – and is currently classified as endangered by the IUCN Red List. Although on a smaller scale, observational tourism can also be stressful for these animals, as it interrupts their feeding behaviours. In addition, it also can cause injuries due to the propellers present on the boats. 

Therefore, countries that harbour Whale Shark populations such as Australia and the Philippines have regulated this activity. In the Philippines, the hunting of whale sharks has also been banned since 2002. 

Pollution as a threat to this giant of the seas

Ocean pollution is the biggest cause of large animals death, especially filter feeders. Although, pollution is much more complex than imagined, for example, the dumping of pesticides into the oceans by industries; pollution of beaches, which generates a large amount of solid waste, especially plastic; increase in heavy metals and trace contaminants/pollutants in water.

These are the biggest killers not only of Whale Sharks but also of large whales, sea turtles, dolphins, other sharks and several species of fish. Ecosystems are also affected, having their balance intensely disturbed.  

Actions that can save the species

The Whale Shark is still little studied by the academic community due to the logistical difficulty in understanding its life history and habitats. From the generated knowledge, more effective measures can be implemented promoting the species’ conservation by developing strategies and action plans.

The human population, in general, must avoid throwing garbage in the street, on the ground, on the beach, and in rivers. Campaigns that promote the cleaning of beaches can bring great results for all the aquatic and semi-aquatic biota.

The Whale Shark is a species with a very important role in the ecosystem it inhabits. They are top predators in their food network. It must remain at sea, peacefully coexisting with other living organisms. Thus, everyone must protect not only the Whale Shark but the entire marine ecosystem.


In this post, we met The biggest fish species and also understood its general anatomy, biology, ecology, main threats and needs for conservation.

If you have any thoughts or doubts, feel free to drop us in a comment below!

Frequently Asked Questions (FAQs): The biggest fish

How old can the whale shark live?

Whale Sharks are estimated to live over 100 years of age. They reach full maturity at around 30 years old.

What is the biggest whale shark?

The largest Whale Shark individual recorded had a length of 12.65 metres and a weight of about 21.5 tons. 

Where to find Whale Shark tourism?

The Whale Shark is found in open tropical ocean waters and is rarely seen in waters with temperatures below 21 degrees Celsius. Some of the tourist places you can see a Whale Shark are: 

–       Isla Holbox, Mexico;

–       South Ari Atoll, Maldives;

–       Cenderawasih Bay, Indonesia;

–       Tofo, Mozambique;

–       Koh Tao, Thailand;

–       Wolf and Darwin Island, Galapagos, Ecuador.

What is the size and weight of the whale shark?

Adult Whale Sharks weigh an average of 19,000 kilograms, but one individual weighing approximately 21,000 kilograms has already been found.


Sequeira, A., Mellin, C., Rowat, D., Meekan, M. G., & Bradshaw, C. J. (2012). Ocean‐scale prediction of whale shark distribution. Diversity and Distributions, 18(5), 504-518.

Colman, J. G. (1997). A review of the biology and ecology of the whale shark. Journal of Fish Biology, 51(6), 1219-1234.

Pravin, P. C. F. P. D. A. (2000). Whale shark in the Indian coast – need for conservation. Current Science, 79(3), 310-315.