These giant sunfish can grow to weigh as much as 5,000 pounds (2,268 kilograms). That's almost as much as a small pickup truck. The huge fish may reach a length of 14 feet (4 meters) from face to tail and 10 feet (3 meters) measured from back to stomach. Fish such as sharks and rays are cartilaginous fish—they don't have bones. Some are heavier than the mola. But among fish with bones, called bony fish, none is larger than the mola.
The mola has an unusual look. It's round. Its tail fin doesn't grow along with the rest of the fish after the mola hatches. It remains short and rounded, adding to the fish's overall round shape. The short fin is called a clavus. Molas use the clavus to steer as they swim. Molas enjoy sunning themselves at the surface of the ocean. This is why they are also called sunfish. They live in tropical and temperate oceans around the world. People sometimes see their tall dorsal fins poking above the surface of the water as they sun themselves, and mistake them for sharks.
When a mola first hatches, it's only one-tenth of an inch long. By the time the fish is fully grown, it gains more than 60 million times its weight from when it hatches. (To compare, you'll probably end up weighing about 30 times what you weighed at birth.) Skin parasites are often a problem for molas. When the fish become infested with parasites, they swim to areas where smaller fish hang out and invite the smaller fish to pick the parasites off as food. When the little fish nibble away at the pesky parasites, they get a meal and they relieve the molas. Another way molas try to get rid of parasites is to leap out of the water and—thwack!—hit the surface of the water hard as they land. They're trying to shake the pests off of their skin. Molas have been known to leap ten feet into the air doing this. Scientists also think that molas spend time sunning to allow gulls to land on the fish and pick off parasites. The fish float on one side as the birds peck them clean. Then the fish flip to the other side so that can be cleaned, too!
Jellyfish are a mola's favorite food. They also eat small fish and microscopic plants and animals found in the water. They have small mouths that look somewhat like a bird's beak. To feed, molas repeatedly suck in and spit out whatever they are feeding on. This process tears the food into smaller pieces that the molas can more easily swallow.
If you are ever snorkeling in an area where molas are found, don't be surprised if one comes to check you out. They are not dangerous, but they are rather curious. They often approach divers and snorkelers—just to investigate.