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Funky Fish

A look at Tierney Thys and her work with the ocean sunfish

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By Stuart Thornton

Friday, October 15, 2010

Looking like a giant silver dollar with fins, the ocean sunfish’s appearance is striking. But its unique shape is only one of many characteristics that cause the creature to stand out, according to Tierney Thys, a National Geographic Emerging Explorer who has traveled the world studying ocean sunfish, also called mola.

“This is the world’s heaviest bony fish,” she says. Some sharks are heavier, but sharks have a light, flexible skeleton of cartilage, not bone. Mola can weigh up to 5,000 pounds (2,268 kilograms).

Thys lists other unique characteristics of mola. “It produces more eggs in one individual than any other vertebrate on the planet. It’s the growth champion of the world, so that from hatching size to adult size it puts on 60 million times its original weight, which just eclipses pretty much everything out there in the vertebrate world. So, it’s this magnificent creature with all these world records to its name, and we don’t really know that much about it at all.”

Like many others, Thys was initially drawn to the ocean sunfish because of its appearance. Having studied fish biomechanics at Duke University, the scientist was puzzled by the shape of the ocean sunfish. It didn’t appear to be very functional.

“You look at the sunfish, and at first glance, it really doesn’t look stunningly efficient,” she says. “It doesn’t really look streamlined. It doesn’t really look very intuitive. So, it grabbed my attention. Why make a fish without a tail? What’s the use of that?”

According to Thys, ocean sunfish don’t really need speed because they pursue a diet of slow, floating jellyfish. A streamlined body or powerful tail are not required. “It’s not a big speedster,” she says. “It doesn’t need to be.”

She and other scientists have debunked a misconception about the fish. Previously, ocean sunfish were perceived as lazy. They seemed to simply float along on the water’s surface, which is one reason they received the common name “sunfish.” Thys and other biologists, however, found that ocean sunfish are actually quite active. “We put these tags on them and found that they are diving industriously up and down, up and down, up and down, up and down to depths as deep as 800 meters, 2,100 feet down,” she says. “They are capable of a tremendous amount of activity.”

Studying Sunfish

The ocean sunfish, found in every ocean in the world, is not endangered. Thys has traveled to Indonesia, Japan, Taiwan, and South Africa to study them.

One unusual characteristic that Thys has observed in sunfish around the world is the high number of parasites on their bodies. Parasites are organisms that feed on other organisms. Most of the parasites that live on mola do not harm the fish. Thys says ocean sunfish are home to parasites because the fish are slow moving, which allows floating parasites to easily secure a place on the sunfish’s thick skin.

On her research expeditions, Thys has observed the ocean sunfish relax in what scientists call “cleaning stations.” In these areas, smaller fish remove the parasites from the larger fish’s body.

“In Bali, coral reef fish, banner fish, and butterfly fish will go in little groups off the reef and find these mola to clean them and give them a spa treatment,” she says.

Even though an ocean sunfish can reach 3.1 meters (ten feet) from snout tip to tail fin, they are prey to larger predators including sharks and killer whales. Off the coast of California, many ocean sunfish are killed by sea lions.

“Certainly in Monterey [California], sea lions rip the fins off and turn them into Frisbees and eat their guts,” says Thys.

Future of the Sunfish

Thys says the greatest danger facing ocean sunfish are not natural predators but fishermen, who often unintentionally catch ocean sunfish while harvesting other species. In the Mediterranean, ocean sunfish are the unintentional victims of drift net swordfish fishing. Off of South Africa, they are caught as fishermen try to bring in horse mackerel.

Thys contends ocean sunfish are one of the most evolved fish in the sea. “[I]t looks like this prehistoric weirdo, but it’s actually a modern marvel in fish terms.”

Recently, Thys received funding from the National Geographic Society to study a population of ocean sunfish located around the Galapagos Islands. In 2011, Thys will head to the Galapagos with a team of four scientists for several weeks. There, the research crew will attach satellite tags to the area’s ocean sunfish. The satellite tags record the fishes’ locations, diving depths, and diving temperatures.

Thys says her primary goal is to characterize the ocean sunfish’s use of the Galapagos ecosystem. Monitoring the fish will allow Thys to determine how they use the area’s animals and plants for food, shelter, or activities like cleaning station “spa treatments.”

"Prehistoric weirdo" is a scientific description of the ocean sunfish.

Photograph courtesy Gulf of the Farallones National Marine Sanctuary/NOAA

National Names
The French call the ocean sunfish "poisson lune," which means "moon fish." In Germany, an ocean sunfish is referred to as "schwimmender kopek" or "swimming head." Meanwhile, the people of the Philippines who speak in the Bisaya dialect say that ocean sunfish are "putol" or "cut short."

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Vocabulary

Term	Part of Speech	Definition
banner fish	noun	tropical marine fish.
biomechanics	noun	study of movement in animals.
bony fish	noun	fish with a skeleton made of bone.
butterfly fish	noun	brightly colored tropical marine fish.
bycatch	noun	fish or any other organisms accidentally caught in fishing gear.
cartilage	noun	strong, flexible connective tissue found in many animals.
cartilaginous fish	noun	fish with a flexible skeleton made of cartilage, not bone.
characteristic	adjective	particular feature of an organism.
coast	noun	edge of land along the sea or other large body of water.
coral reef	noun	rocky ocean features made up of millions of coral skeletons.
debunk	verb	to prove false or wrong.
drift net	noun	extremely large fishing net that can drift with currents or tides.
eclipse	verb	to block out or overshadow.
efficient	adjective	performing a task with skill and minimal waste.
evolve	verb	to develop new characteristics based on adaptation and natural selection.
fin	noun	device fixed to the bottom of a surfboard to aid in control. Also called a strut or skeg.
flexible	adjective	able to bend easily.
Frisbee	noun	brand of round, circular discs used as throwing toys and athletic equipment.
functional	adjective	usable.
hatch	verb	to emerge from an egg.
horse mackerel	noun	small ocean fish.
industriously	adverb	with hard work and dedication.
initially	adverb	at first.
jellyfish	noun	type of marine animal, not a fish, with a soft body and stinging tentacles.
killer whale	noun	carnivorous whale, actually the world's largest species of dolphin. Also called an orca.
magnificent	adjective	very impressive.
misconception	noun	misunderstanding or false statement.
mola	noun	gigantic ocean fish with a circular body. Also called the ocean sunfish.
ocean sunfish	noun	gigantic ocean fish with a circular body. Also called the mola.
organism	noun	living or once-living thing.
parasite	noun	organism that lives and feeds on another organism.
predator	noun	animal that hunts other animals for food.
prehistoric	adjective	period of time that occurred before the invention of written records.
prey	noun	animal that is hunted and eaten by other animals.
satellite tag	noun	device attached to animals that can track their movement using satellites and GPS technology.
sea lion	noun	marine mammal.
shark	noun	predatory fish.
silver dollar	noun	coin made of light-colored metal, including silver, tin, and zinc.
skeleton	noun	bones of a body.
snout	noun	protruding nose and jaw of an animal such as a pig.
swordfish	noun	ocean fish with a large, pointed upper jaw
tremendous	adjective	very large or important.
unintentional	adjective	accidental, or not on purpose.
unique	adjective	one of a kind.
vertebrae	plural noun	(singular: vertebra) bones that make up the spinal column, or backbone, of an animal.
spa	noun	facility, usually with mineral hot springs, offering health benefits.