The Mola Mola or ocean sunfish is a gentle giant, a peaceful head of a fish with a large dorsal and ventral fin, and a clavus instead of a tail. It’s the heaviest bony fish that we know of, at 545 to 2,205 lbs (247 to 1,000 kg) on average. Mola is Latin for millstone, which refers to its gray, flat, and roundish appearance. From National Geographic:
Mola are found in temperate and tropical oceans around the world. They are frequently seen basking in the sun near the surface and are often mistaken for sharks when their huge dorsal fins emerge above the water. Their teeth are fused into a beak-like structure, and they are unable to fully close their relatively small mouths.
Ocean sunfish can become so infested with skin parasites, they will often invite small fish or even birds to feast on the pesky critters. They will even breach the surface up to 10 feet (3 meters) in the air and land with a splash in an attempt to shake the parasites…
Their food of choice is jellyfish, though they will eat small fish and huge amounts of zooplankton and algae as well. They are harmless to people, but can be very curious and will often approach divers.
This one in the video seems alright with having some temporary company. Plus, watch how their fins move (at 2m17s) when a few of them swim quickly away.
Related reading: oceansunfish.org.