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Why Does the Ocean Sunfish Produce So Many Eggs?

The ocean sunfish, or Mola mola, is a reproductive powerhouse, producing more eggs than any other known vertebrate—up to 300 million at a time. This staggering number ensures the survival of the species amidst numerous predators and a harsh marine environment. But what drives this extraordinary fecundity? Uncover the secrets of the sunfish's reproductive strategy as we dive deeper.

The ocean sunfish, also known as the common mola, is the world’s heaviest bony fish. It can grow as large as 5,000 pounds (2,300 kg) and can measure 14 feet (4.3 m) when measured from the top of its dorsal fin to the bottom of its anal fin. This oddly-shaped fish without a tail loves to float on its side at the surface of the sea and soak up the sun.

It's also among the animal kingdom’s most prolific egg producers, releasing about 300 million eggs during the spawning season. These tiny eggs, though, hardly ever become adult fish. Scientists say that despite all those eggs, a spawn usually produces just two adult sunfish.

More sunfish surprises:

  • The ocean sunfish is always on the lookout for jellyfish. But since jellyfish are almost entirely made of water and are low in nutrients, a growing ocean sunfish has to eat a whole lot to put on hundreds of pounds a year, its usual growth rate.

  • On the other hand, adult sunfish can fall prey to sea lions, killer whales and large sharks. In California, sea lions have been known to bite off the fins of small ocean sunfish and then play with them like Frisbees.

  • The ocean sunfish has also made its mark on popular culture. A simulation game called Survive! Mola Mola! is a popular app purchase in some Asian countries. The Japanese edition of the game has reportedly been downloaded more than four million times.

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    • Although the ocean sunfish produces around 300 million eggs, only two will usually make it to adulthood.
      Although the ocean sunfish produces around 300 million eggs, only two will usually make it to adulthood.