Mola mola is a giant disk with a clipped-off look
Ocean sunfish (Mola mola) rank among the heaviest ray-finned fishes and serve as the type species of genus Mola. Biologists still lack clear maps of mating grounds, early life, and migrations, even though sea lions, orcas, and sharks successfully hunt the adults.
Mature fish average 1.8 m long and 2.5 m from fin tip to fin tip, usually weighing 247 to 1,000 kg. The biggest measured, stranded in New Zealand in 2006, was 3.3 m long and 2,300 kg. It was long misnamed the heaviest bony fish; that title belongs to its relative Mola alexandrini. Names across Europe mostly mean moon fish, while German also says swimming head, Polish head alone, Scandinavian and Finnish words mean lump fish, and the Chinese name translates as overturned car fish. English sunfish refers to its habit of basking at the surface.
Guillaume Rondelet described it in 1554, comparing it to a sucking pig, and it was first filed among the pufferfish. The epithet mola is Latin for millstone, for its grey, rough, round body. Like puffers it has a beak of four fused teeth, and its fry look like spiky puffers. A rudder-like clavus, formed where the dorsal and anal fins meet, replaces the tail. Its spine is shorter relative to the body, with fewer vertebrae, than in any other fish.
Much of the skeleton is light cartilage, which helps it reach sizes impractical for other bony fishes. Lacking a swim bladder and the usual trunk muscles, it floats on a stiff gelatinous layer that is about 90 percent water, laced with collagen and elastin. The belly skin can be 7.3 cm thick, rough as sandpaper and coated in mucus rather than scales, and it can darken when attacked. Over 40 parasite species may live on or inside it. Near the surface its fin is sometimes taken for a shark's, but it sculls from side to side.
Japan, Korea and Taiwan eat it as a delicacy, while the European Union bans selling molid products, and many are caught in gillnets. Researchers use aerial surveys, pop-off satellite tags, genetics and amateur sightings to fill in its unknown life history.
Source: Ocean sunfish
