Unraveling the Mysteries of the Ocean Sunfish

Marine biologist Tierney Thys and researchers at the Monterey Bay Aquarium are learning more about one of the largest jellyfish eaters in the sea

The ocean sunfish is the heaviest bony fish in the world; it can grow more than 10 feet long and pack on a whopping 5,000 pounds, and yet its flat body has no real tail to speak of. (Mike Johnson)

Part of the appeal of the ocean sunfish, or Mola mola, is its unusual shape. The heaviest bony fish in the world, it can grow more than 10 feet long and pack on a whopping 5,000 pounds, and yet its flat body, which is taller than it is long, has no real tail to speak of. (“Mola” means “millstone” in Latin and refers to the fish’s disc-like physique.) To motor along, the fish uses powerful dorsal and anal fins.

The mola is something of a star at the Monterey Bay Aquarium, the only facility in North America to currently exhibit the bizarre-looking fish. “You just don’t see anything like that,” says John O’Sullivan, curator of field operations at the aquarium. When the nearly four-foot-long sunfish swims slowly across the two-story window of the Open Sea gallery, its large eyes pivoting as it travels, it is as if the whole building shifts with the weight of people gathering in awe,  he says.

For being so visually arresting (it is on the bucket list of many scuba divers), the mola is a bit of a mystery; very little is known about its biology and behavior. Tierney Thys, for one, is trying to change this.

“I always feel that nature reveals some of her greatest secrets in her extreme forms,” says Thys at her home perched like a tree house in the hills of Carmel, California. With reports suggesting that jellyfish may be on the rise, the marine biologist is even more compelled to understand the lives of molas, which are voracious jelly eaters.

If the sparkle in her eye when she talks about her many encounters with wild molas doesn’t give away her passion for the species, her impressive collection of tchotchkes does. Thys shows me playing cards, postage stamps and chopsticks decorated with molas, stuffed animals, even crackers (like Pepperidge Farm’s “Goldfish,” only shaped like sunfish), laughing at the range of mola products she has found in her travels around the world studying the fish.

Thys’s introduction to the mola came in the early 1990s when she came across a photo of one while doing graduate work in fish biomechanics at Duke University. A tuna, she explains, is sleek, like a torpedo; its form gives away its function: to travel great distances with speed. “But you look at a mola,” she says, “and you think, what is going on with you?”

Molas emerged between 45 million and 35 million years ago, after the dinosaurs disappeared and at a time when whales still had legs. A group of puffer fishes—“built like little tanks,” says Thys—left coral reefs for the open ocean. Over time, their clunky bodies became progressively more “abridged,” but never as streamlined as some other deep-sea fishes. “You can only divorce yourself from your bloodlines so much,” says Thys. “If your grandmother had a big bottom and your mother had a big bottom, you are most likely going to have a big bottom. There is not much you can do!”

From her advisor, she learned that the Monterey Bay Aquarium was on the cusp of being able to display molas. The aquarists had a few fish in quarantine tanks, and Thys was able to spend some time at the aquarium studying their swimming mechanics and anatomy.

In 1998, Thys moved to the Monterey Peninsula, where she worked as a science editor and later director of research at Sea Studios Foundation, a documentary film company with an environmental focus. She served as the science editor for the foundation’s award-winning series “The Shape of Life,” about evolution in the animal world, which aired on PBS; the mola had a cameo. Meanwhile, Thys rekindled her relationship with the aquarium.

At the aquarium, O’Sullivan tested tags on captive molas, and in 2000, he and Thys began tagging wild molas in southern California. Chuck Farwell, curator of pelagic fishes at the aquarium, had established a relationship with Kamogawa Sea World in Japan, and he and Thys began tagging there as well. The Japanese have been the leaders in exhibiting molas. Historically, the culture holds the mola, known as manbou, in high regard. In the 17th and 18th centuries, people gave the fish to shoguns in the form of tax payments. Today the mola is Kamogawa’s official town mascot.


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