Largest and one of the most unusual ray-finned bony fishes
Ocean sunfish (Molidae) are large pelagic fish found in temperate and tropical marine waters worldwide. They feed primarily on jellyfish, but also eat algae, crustaceans, mollusks, and small fish. In addition to being quite large [mola mola can grow to a length of seven feet and weigh well in excess of two tons], they look like the rear third of the body has been chopped off. They lack caudal (or tail) bones and the caudal fin is almost vestigial. The ocean sunfish, though, has large dorsal and anal fins, which provide almost all of the animal’s propulsive power. The small pectoral fins serve as stabilizers. The relatively small mouth contains long, claw-like teeth. Ocean sunfish lack swim bladders. The adult female may be the most fecund of fishes, producing up to 300 million eggs. Coloring ranges from gray to brown to blue, with lighter coloring on the lower portion, and variable spots on the sides. The skin is thick and leathery, lacking traditional scales, but covered in mucus, which is susceptible to parasites. To rid itself of these pests, the ocean sunfish will sometimes float on the surface while lying on its side. Seabirds land on the animal and consume the parasites. Alternatively, the sunfish swims slowly in patches of algae or flotsam where halfmoon and other cleaner fish congregate. The cleaner fish then perform the same service as seabirds. Because ocean sunfish live almost exclusively in pelagic waters, many details of their lives are unknown, such as life expectancy. In those rare instances when divers have encountered sunfish, the animals have proven quite docile, allowing humans to approach closely. Most people do not like the flesh of the ocean sunfish, so it is not targeted commercially.