The ocean sunfish (mola mola) eats a much wider variety of food than most people think. For decades, scientists assumed these enormous fish survived almost entirely on jellyfish. But DNA analysis of stomach contents has revealed at least 41 different prey items, including crustaceans, small fish, and squid, with jellyfish making up only about 16% of consumed prey in some studies.
More Than Just a Jellyfish Eater
The old image of the mola mola as a dedicated jellyfish specialist came from limited evidence: fatty acid tests on just four individuals and observations of sunfish swimming near jellyfish blooms in the Irish and Celtic Seas. It made intuitive sense. The sunfish has a small, beak-like mouth that doesn’t close fully, and jellyfish are slow-moving, easy targets. But when researchers used DNA barcoding to identify prey remains in 57 sunfish, the picture changed dramatically.
Crustaceans and small bony fish turned up far more often than jellyfish. Researchers even visually confirmed a freshly eaten conger eel larva in one sunfish’s stomach. Stable isotope analysis, which reveals what an animal has been eating over weeks or months rather than just its last meal, confirmed the same thing: mola mola feed broadly within coastal food webs.
That said, jellyfish are still an important part of the adult diet, especially in certain regions. In the northeast Atlantic, sunfish regularly feed on barrel jellyfish, compass jellyfish, and lion’s mane jellyfish, and they’re frequently spotted near large jellyfish blooms. Scientists believe sunfish play a meaningful role in controlling these blooms, which have been increasing in many ocean regions.
How Their Diet Changes With Size
Smaller sunfish eat different prey than larger ones. Juveniles and sub-adults feed mainly on small crustaceans and bony fish, often targeting species that live near the seafloor or in coastal waters. As sunfish grow larger, their diet shifts toward more open-ocean, pelagic prey, including a higher proportion of jellyfish and other gelatinous animals like salps and siphonophores.
This progression makes sense from a practical standpoint. Young sunfish are small enough to hunt quick, energy-dense prey like tiny fish and shrimp-like crustaceans in shallower water. As they reach adult sizes of over a meter in length, they increasingly rely on the soft-bodied prey that their specialized anatomy is built to handle.
Built for Eating Jellyfish
While mola mola turn out to be more versatile eaters than expected, their anatomy is still remarkably well-suited to gelatinous prey. They feed by suction, drawing water and food into their mouths. Deep in their throats sit rows of pharyngeal teeth, small, claw-like structures normally tucked beneath soft tissue. When engaged, a strap-shaped muscle pulls these teeth outward, much like a cat extending its claws.
These throat teeth act as a retention cage. Jellyfish are slippery and mostly water, making them difficult to grip and swallow. Sunfish solve this by jetting water during feeding, and their pharyngeal teeth catch and hold the gelatinous tissue with 70 to 100 percent success in laboratory simulations. Even at 50 times the force of normal jetting, the teeth stayed locked in place, showing they’re built with a huge margin of safety. This adaptation is a striking case of convergent evolution, mirroring the throat spikes found in unrelated animals like leatherback sea turtles, which face the same challenge of keeping jellyfish from sliding back out.
Where and When They Hunt
Mola mola don’t just drift around the surface waiting to bump into food. Tagged sunfish in the northwest Atlantic spend over 80% of their time in the top 200 meters of the water column, but they regularly dive much deeper. The deepest recorded dive reached 844 meters, well into the cold, dark midwater zone, and temperatures experienced by tracked fish ranged from 6 to 30°C.
Their diving follows a daily rhythm tied to finding prey. During the day, sunfish make repeated dives below the thermocline (the boundary where warm surface water meets colder deep water). At night, they stay in shallow water near the surface. This pattern mirrors the behavior of blue sharks, swordfish, and tunas, all of which are thought to follow the daily vertical migration of the small organisms they eat. Many crustaceans and small fish rise toward the surface at night and sink to deeper water during the day, and sunfish appear to track them.
Seasons matter too. In summer, sunfish in the northeastern United States stayed in shallower water and spent more time at the surface. When those same fish moved south into the Gulf Stream during winter and spring, they avoided the surface almost entirely and shifted to deep dives of 400 to 800 meters. This seasonal change likely reflects different prey availability and ocean conditions in each region.
Why the Jellyfish Myth Persisted
Part of the reason scientists long classified mola mola as jellyfish specialists is that jellyfish digest slowly and are easy to spot in stomach contents. Crustaceans and small fish break down quickly, so by the time a sunfish was examined, those prey items had often disappeared, leaving behind the more resistant gelatinous remains. DNA barcoding solved this problem by identifying prey from genetic traces rather than visual inspection, revealing all the smaller, faster-digesting food that had been missed for years.
The practical takeaway is that mola mola are opportunistic feeders. Adults lean heavily on jellyfish in some environments, but the species as a whole consumes a cosmopolitan diet that spans crustaceans, fish larvae, squid, and various gelatinous organisms. Their role in the ocean is more complex than the “jellyfish vacuum” reputation suggests, and their feeding connects them to food webs at multiple depths and across multiple prey groups.