Animal World Records

Biggest Fish

A whale shark at Georgia Aquarium
Image Source: Stefan

To celebrate International Whale Shark Day, The Nature Nook will be taking a brief look at these amazing aquatic leviathans. Not only is the whale shark the biggest species of shark in the world, it’s also the biggest of all the planet’s approximately 34,000 species of fish and the largest living non-mammalian vertebrate. Capable of reaching 12 m in length – double that of a great white shark – and weighing up to 21 tonnes, the whale shark easily rivals many prehistoric dinosaurs in size. In the modern era, only a few whales grow larger.

Despite its immense bulk, the whale shark is a gentle giant – it poses no threat to humans whatsoever. One of only three filter-feeding sharks in the world, it somehow manages to achieve and sustain its phenomenal size on just a briny broth of tiny, usually planktonic, animals. This colossal creature cruises around with its 1.5 metre-wide mouth open, sucking in vast mouthfuls of water – enough to fill an Olympic-sized swimming pool every 100 minutes – and expelling it through its gills. Any small organisms that it ingests at the same time – krill, copepods, small fish and squid, for example – are trapped by sieve-like membranes in the gills, concentrated into a ball, and then swallowed. The whale shark has up to 350 rows of minuscule teeth (around 4,000 of them in total, each no bigger than a grain of rice), but because the animal does not chew its food, these teeth play no role in feeding and are likely just vestigial remnants.

A whale shark - the biggest fish in the world - swimming in the ocean
The arrangement of white spots on a whale shark’s body is unique to each animal and so can be used as a ‘fingerprint’ of sorts to identify individuals.
Image Source: Peakpx

Though it’s hard to estimate overall numbers, the whale shark is believed to be in decline and was officially classified as Endangered on the IUCN (International Union for Conservation of Nature) Red List of Threatened Species in 2016. The greatest threat to this species is the fishing industry. In some cases, they are caught by accident – even an animal as enormous as the whale shark is not immune from getting tangled in fishing nets.

But in many cases, the whale shark is actively, deliberately fished. Boats target this species for its meat, oil, gills and fins. Fins are considered to be particularly valuable because they are used as ingredients in shark fin soup and some traditional cures, especially in China. Shark fins are among the most expensive of all seafood products, commonly retailing at US$400 per kilogram. Some buyers regard the whale shark as a trophy species, paying between $10,000 and $20,000 for a single dorsal fin.

A whale shark being followed by suckerfish, or remoras
The whale shark has the thickest and toughest skin of any living animal, measuring up to 15 cm thick on the back.
Image Source: Derek Keats

Whale sharks have roamed the oceans for 60 million years – yet they remain very mysterious creatures. Many aspects of their biology, behaviour, migration and life cycle remain poorly understood. No one knows, for example, how long these docile giants can live for – recent studies have given a rather vague estimate of between 80 and 130 years. And although we know that females give birth to live young, we still do not know for definite where their birthing grounds are, since pupping in this species has never been observed. The only pregnant female to have been physically examined was accidentally caught in a Taiwanese net, where she died. After being passed on to scientists to be studied, it was discovered that she had 304 embryos inside her. These ranged from recently-fertilised to near-term, all with the same father, indicating that female whale sharks only mate once and then store sperm to fertilise their eggs.

International Whale Shark Day aims to increase awareness about this magnificent animal and the threats it faces, and encourages marine conservation efforts aimed at protecting it. There is hope yet for this gargantuan denizen of the ocean, but only by unlocking its secrets can we secure a future for the planet’s biggest fish.


  • Jason Woodcock

    With a background in conservation and animal behaviour studies, Jason's passion lies in the natural world. He adores all things nature and enjoys nothing more than spotting rare and interesting species out in the wild. He has also worked in a zoo and knows plenty about keeping the animals inside our homes healthy and happy, too.

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