The Record-Breaking 6,000-Pound Sunfish: Largest Bony Fish Ever Documented

The giant sunfish found floating near Faial Island in the Azores archipelago Courtesy of the Atlantic Naturalist

Last December, scientists in Portugal got word that fishermen and boaters had spotted an enormous dead sunfish floating in the central North Atlantic. Researchers initially had doubts about the fish’s reported size, but when they finally reached the carcass near Faial Island in the Azores archipelago, they almost couldn’t believe their eyes.

Now, after weighing, measuring and analyzing the bump-head sunfish (Mola alexandrini), scientists believe it’s the heaviest bony fish ever discovered. Weighing in at roughly 6,050 pounds—the size of a large SUV—the fish was 882 pounds heavier than the reigning bony fish world record-holder, a 5,070-pound sunfish discovered off the coast of Japan in 1996.

Scientists shared more details about the giant sunfish found in the Azores last year in a new paper published last week in the Journal of Fish Biology.

Bony fish is an umbrella term used to describe the 29,000 species of aquatic wildlife with skeletons made at least partially from bone, rather than cartilage. These diverse swimmers range from teeny-tiny pygmy goby to sunfish and every size in between. More than 90 percent of all fish are bony fish; the category excludes rays, sharks and other marine wildlife with cartilaginous skeletons.

Sunfish have huge, hulking round bodies, dorsal and anal fins, and a unique rounded rudder called a clavus formed when their back fin naturally folds into itself, per National Geographic. Droves of parasites feed on their rough, gray skin. Sunfish are awkward swimmers, and they can’t fully close their mouths, which are tiny compared to their massive bodies. Sunfish prefer to munch on jellyfish, but they also eat algae, zooplankton and small fish.

When massive sunfish swim or float near the ocean’s surface, people often mistake them for sharks. But though they can be quite curious, sunfish are largely harmless.

Scientists first recognized bump-head sunfish as a distinct species in 2018. They are related to ocean sunfish (Mola mola) but can be twice as heavy.