Farallones Marine Sanctuary Association protecting our ocean wilderness through public stewardship
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Wildlife Spotlight: Ocean Sunfish (Mola mola)

By Stefan Marti
Published: November 2006

A diver next to a huge Mola mola.
A diver swims up to a mola. Credit NOAA

Imagine a giant 10-foot-tall fish with no tail lying on its side, sunbathing at the ocean’s surface.  Well, there you have the Ocean Sunfish, or Mola mola, the largest bony fish in the world.  

The ocean sunfish is a flat, oval-shaped fish with a huge dorsal and anal fin, giving it the shape of a propeller.  The two fins, which flap from side to side, are its principal source of locomotion.  Although the sunfish has a truncated body, it does have a short, round tail (clavus) that acts as a rudder.

Ocean sunfish are pelagic (deep water) fish found in all oceans.  They are often spotted in the Gulf of the Farallones National Marine Sanctuary. 

Typically silvery in color with a slight opalescent sheen, ocean sunfish have rough, sandpapery skin covered with mucus.  Their tiny mouths cannot be closed, and their top and bottom teeth are fused to form a beak.

Drawn to the sun’s warm rays, these sunfish often float on their sides near the surface of the ocean.  Their average weight is one ton—500 pounds heavier than a horse—and their average length from the tip of the snout to the end of the clavus is 6 feet (1.8 meters).

Mola floating at the surface. Credit NOAALast week on a research cruise aboard the new research vessel Fulmar, Beach Watch Manager Shannon Lyday spotted several ocean sunfish on the surface.  "It is exciting to see these amazing creatures within the Sanctuary.  It is important to protect open ocean habitat for these graceful behemoths."

Diet

Ocean sunfish feed on jellyfish and other gelatinous, soft-bodied zooplankton as well as small fish, squid and crustaceans. Although they generally feed in deeper waters, at times they forage near kelp beds in shallow coastal areas.

Sponges, serpent star bits, eel grass and deepwater eel larvae have been found in their guts, indicating that they forage at the surface, among floating weeds, on the seafloor and into deep water.

Predators

When ocean sunfish are smaller, their predators are orcas, sea lions, dolphins and marlin. Only orcas will attack large adults.

During the fall months in Monterey, sea lions can be seen ripping the fins off ocean sunfish and slamming them against the sea’s surface. Presumably this action helps the sea lions tear through the molas’ tough leathery skin. After tossing them through the air for several minutes, the lions often simply abandon their prey, and the hapless, finless molas sink to the seafloor where they are consumed slowly by bat stars.

However, the most deadly predator for ocean sunfish are humans.  Although people in China and Japan eat ocean sunfish, most of the sunfish caught are bycatch, killed by fishermen looking for other species. 

Mola is the most common bycatch of the drift net fishery, which targets broadbill swordfish off California and Oregon.  Nearly 40% of all discards are mola.

Mola mola.Amazingly, ocean sunfish still have healthy populations.  This is most likely due to the incredible number of eggs they lay.  The Mola mola may have the highest reproductive rate of all vertebrates. A four-foot female contains approximately 300 million eggs.

Protecting Molas

When you buy swordfish, help the ocean sunfish by looking for swordfish that is sustainably caught.  And next time you are on the water and see an enormous sunbathing fish, say hello to the Mola mola.