Which Are The Largest, Longest And Heaviest Animals Of The Ocean?

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The largest animal on the planet is the Blue Whale. The largest fish is the Whale Shark. Both of these marine mammals are filter feeders.

The ocean is home to some of the weirdest, creepiest and largest living creatures on this planet. A mere glimpse of them spawned countless tales of sea monsters, such as the Loch Ness Monster and the Kraken. Reality might not be as terrifying as these fantastical monsters, but it doesn’t make any of these creatures any less amazing. They are big and they come in all shapes and sizes. So, here’s a list of some of the ocean’s superlative animals.

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The Largest Animal Of The Ocean: The Blue Whale, Balaenoptera musculus.

From an aerial view, a blue whale swims under the surface in Monterey Bay(Chase Dekker)s
The largest animal the Earth has ever seen. (Photo Credit : Chase Dekker/Shutterstock)

It is the biggest animal in the ocean to have ever existed. To measure the blue whale, you would need approximately 108 standard 12-inch rulers placed end to end to measure the biggest blue whale out there. That’s a lot of rulers. This incredible creature weighs an astounding 177 tons, the same as about 30 African Bush Elephants, the largest land mammal.

Its relatives are other giant whales called Baleen Whales, suborder Mysticeti. The whales in this suborder differ from other whales in that they have something called baleen plates, instead of teeth. Other humongous whales in this suborder are the fin whale, the second largest after the blue whale, coming in at 26 m (85 ft), as well as the humpback whale and the Sei whale.

Filter Feeding

Even though baleen whales reach such enormous sizes, they feast on surprisingly small creatures—krill, zooplankton and small fish. An adult whale can eat about 40 million krill a day! They just open their mouths, position themselves properly and then suck in all the krill in one gulp—a feeding method called filter feeding.

Also Read: Why Are Marine Mammals, Like Whales, Larger Than Land Mammals?

The Largest Fish: The Whale Shark, Rhincodon typus

whale shark cruising in crystal clear water(Leith Holtzman)S
The Whale Shark, the largest fish in the world, swimming in clear waters, with its unique dotted pattern on display. (Photo Credit : Leith Holtzman/Shutterstock)

The Whale Shark is so big that it’s called a whale, but it is, in fact, a shark. It is part of the class Chondrichthyes, which contains all cartilaginous fish, including sharks, rays and skates. The maximum recorded verifiable length is 18.8 meters, while some other sources have even reported seeing whale sharks at a staggering 20 meters (65.6 feet) in length!

With its characteristic dotted pattern, the whale shark is found globally, but prefers warmer, more tropical climates like those of Western Australia, where they are frequently sighted.  This massive fish roams the open water, filter feeding like baleen whales, coming to the surface to feed.

The Whale Shark is known as a gentle creature that minds its own business and feeds on krill. There have been a few times when Whale Sharks have rammed into the sides of boats, mostly while feeding, and these strikes do not appear to be malicious in nature.

Whale Sharks are listed as a vulnerable species.

Also Read: Can A Whale Swallow You Whole?

The Heaviest Jellyfish: Nomura’s Jellyfish, Nemopilema nomurai

the largest jellyfish, the Nomura’s jellyfish.
The largest jellyfish, the Nomura’s jellyfish. (Photo Credit : Flickr)

When most of us think of jellyfish, we think of ethereal floating tentacled bells that can cause you a lot of pain if you run into one at the beach. However, we rarely think of them as gigantic, or even heavy. Well, the Nomura’s Jellyfish should change that.

Coming in at 2 meters (6.5 feet) in diameter and weighing 200 kilograms (440.9 pounds), the Nomura’s Jellyfish is massive. Adults can gain 2 to 10% of their body weight each day, so a 100 kg (220.47 lb) individual could gain 2 kg (4.4 lbs) every day.  However, since jellyfish cannot actively find a new food source, their growth depends on the availability of food around them. Jellyfish eat a variety of things, ranging from plankton to shrimp.

The Heaviest Bony Fish In The Seas: The Ocean Sunfish, Mola mola

Enormous Sunfish
A giant ocean sunfish with a weight estimated at 1.587 kg (3,500 pounds) (Photo Credit : P.V. Reyes of Avalon/Wikimedia Commons)

If you’ve ever wondered what a 3 meter (9.8 ft) disc would look like with fins, then you’ve probably imagined an ocean sunfish. This odd-looking fish can weigh as much as 2,300 kg (5070.6 lbs). Although the whale shark is also a fish, sharks have cartilage for their skeleton, not bones. Thus, the title of the heaviest bony fish (and some might say the oddest) goes to the sunfish.

Its scientific name means millstone, due to its undeniable millstone shape. The common name, ocean sunfish, comes from their habit of sunbathing so that aquatic birds can nibble the parasites on the back of the fish.

To become as large as the ocean sunfish, which is to say about the size of a rhino, it has to eat. Its favorite meal is jellyfish. The sunfish spends a lot of its time eating a lot of jellyfish, probably not because it loves the taste, but because floating blobs don’t pack a very filling or nutritious meal.

The Longest Bony Fish – The Oarfish, Regalecus glesne

giant oarfish (Regalecus glesne)(Dotted Yeti)s
The Oarfish is a very very long fish. (Photo Credit : Dotted Yeti/Shutterstock)

If the ocean sunfish looked like a dinner plate, then the oarfish looks like an accompanying utensil. The oarfish is aptly named for its length and thinness; it slithers around in the seas, intriguing and scaring people in equal measures. If any fish deserves the title of a sea monster, it is this one!

The longest ever recorded is 8 m (26.2 ft) long, but some have reported oarfish up to 11 m (36 ft)! The latter length might not be reliable due to an odd ability of the oarfish to detach their tail from their bodies, just as lizards do with their tails. So, some past records have assumed the length of the tail, which leads to a very long oarfish.

Why the fish detaches its tail isn’t clear. Oarfish prefer the deep open oceans over shallower waters, making it difficult for scientists to observe them. Specimens are difficult to come by, and good ones are even rarer. Since scientists have such limited information on this sea serpent, it is also difficult to estimate the maximum length to which the oarfish could grow. With that said, 8 meters is the length of 4 very tall people, which is still pretty impressive!

Some Honorary Mentions:

The oceans offer so many strange life forms to observe, it’s impossible to write about all of them. Here are a few that just missed the list.

The Largest Clam: The Giant Clam, Tridacna gigas

The Giant Clam, Tridacna gigas, is the largest clam you’re likely to ever see. You will not find this 1.37 m (4.5 ft) clam, which potentially reaches weights of 333 kgs (734 lbs), in your clam chowder anytime soon. Described as a man-eating clam, the Giant clam is listed as a vulnerable species on ICUN’s list. There have been several efforts made to aquaculture the clam and release it back into the wild.

The giant clam, the colossal squid and the giant squid, the honorary mentions of our list.
The giant clam, the colossal squid, and the giant squid, the honorary mentions of our list. (Photo Credit : kai egan/Shutterstock & GNU Free Documentation License & NTNU Vitenskapsmuseet/Wikimedia Commons)

The Heaviest Invertebrate In The Ocean: The Colossal Squid, Mesonychoteuthis hamiltoni

If squids and octopuses, aka cephalopods, aren’t on a list of ocean superlatives, that list is incomplete. The Colossal squid, Mesonychoteuthis hamiltoni, is the heaviest invertebrate and probably terrorized many ships, inspiring all sorts of terrifying stories. The heaviest a Colossal Squid has been recorded at is 495 kgs (1091 lbs), and measuring as long as 2 humans. The Colossal squid often gets confused with another big cephalopod, the Giant Squid, Architeuthis dux. It seems that whoever named them didn’t have a dictionary or much imagination on hand, leaving many mistaking the two. The Giant squid takes the longest cephalopod title, coming in at 12 meters (39 ft) thanks to its trailing tentacles.

Size is important for living things. It determines how their bodies work and how well they can adapt to certain environments. Certain sea animals, like whales, have to be large so that they don’t lose too much heat to the freezing cold waters they swim in. Studying size is also important for scientists. Knowing size allows them to make predictions about metabolism, nutritional requirements and certain behaviors. In the end, though, each animal is ideally suited to its environment. If it happens to also be big and sometimes scary in appearance, it will become the stuff of human legends!

Also Read: Why Do Some Creatures In The Deep Sea Grow To Enormous Sizes?

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References (click to expand)
  1. McClain, C. R., Balk, M. A., Benfield, M. C., Branch, T. A., Chen, C., Cosgrove, J., … Thaler, A. D. (2015, January 13). Sizing ocean giants: patterns of intraspecific size variation in marine megafauna. PeerJ. PeerJ.
  2. Blue whale - Australian Antarctic Program. The Australian Antarctic Division
  3. Tou, J. C., Jaczynski, J., & Chen, Y.-C. (2008, June 28). Krill for Human Consumption: Nutritional Value and Potential Health Benefits. Nutrition Reviews. Oxford University Press (OUP).
  4. Gearty, W., McClain, C. R., & Payne, J. L. (2018, March 26). Energetic tradeoffs control the size distribution of aquatic mammals. Proceedings of the National Academy of Sciences. Proceedings of the National Academy of Sciences.
  5. Chondrichthyes - UCL. University College London
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About the Author

Salama has a degree in life sciences and biochemistry from St. Xavier’s College, Mumbai, which she puts to good use as a science writer and video producer at ScienceABC.com. She’s interested in the history of science; how science has shaped how we understand the world and society.