What do you call a fish without a tail? You might say it looks like the world’s ugliest pillow, with huge triangular fins, yet totally tailless. Oh, and it's about the size of a Cadillac.
What does my friendly neighborhood ichthyologist say about this? That behemoth is a mola, also called the ocean sunfish. “Mola” comes from the Latin for millstone, and it did resemble one rolling my way. The heaviest ever found was just over 6,000 pounds, making it the largest bony fish out there. And they really don’t have tails: their back fin folds in on itself as they grow, leaving a rounded hindquarters called the clavus. The clavus acts like a ship’s rudder, useful for steering but not propulsion.
Despite their awkward appearance, molas are fantastic swimmers—by flapping their large dorsal and ventral fins, they can travel nearly thirty miles a day, and dive thousands of feet deep. They can even launch themselves into the air!
Molas can often be spoted lying flat like a lumpy pillow, basking just under the surface. They like to float, which exposes their many parasites to hungry seabirds, who happily peck the parasites away. Those birds would gladly eat the mola too, if its skin weren’t so thick. As for the swimming, molas get curious about nearby humans. Luckily, they’re totally harmless.
A special thank you to Natasha Phillips for reviewing this episode’s script!
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Sources and Further Reading
Kemp, Daniel. “The Solar-Powered Fish with Jellies in Their Bellies: Molas.” U.S. Fish and Wildlife Service, September 26, 2022.
“Ocean Sunfish.” National Geographic.
Parkinson, Kerryn. “Ocean Sunfish, Mola mola (Linnaeus, 1758).” Australian Museum, August 12, 2023.
Thys, Tierney M., John P. Ryan, Heidi Dewar, Christopher R. Perle, Kady Lyons, John O'Sullivan, Charles Farwell, Michael J. Howard, Kevin C. Weng, Bertha E. Lavaniegos, Gilberto Gaxiola-Castro, Luis Erasmo Miranda Bojorquez, Elliott L. Hazen, and Steven J. Bograd. “Ecology of the Ocean Sunfish, Mola mola, in the southern California Current System.” Journal of Experimental Marine Biology and Ecology, vol. 471, October 2015. https://doi.org/10.1016/j.jembe.2015.05.005.
