The term "Ocean Sunfish" refers to the family Molidae. The family is comprised of three genra and 5 species split between those three genra. All five species have a similar shape. They are larger fish whose bodies are flattened laterally. This means that they look like they have been squeezed from the side. Their body has been described as a thick head. Their dorsal and anal fins are both lengthened, which can make some species as tall as they are long.
There is a small river fish found in the United States called the freshwater sunfish, but it is unrelated to the Ocean Sunfish and, surprisingly, doesn't look like it at all.
The Ocean Sunfish is also the common name for a particular species of sunfish (Mola mola) found throughout temperate and tropical waters. It is one of the two heaviest bony fish, sharing the title with another species in the Mola genus, the Southern Sunfish. Both fish can reach a weight of about 2000kg (4 400lbs). They are large fish, having a maximum length of about 3m (10 ft) and a fin span of about 4.2m (13.9ft). The caudal or tail fin of the sunfish has adapted into a structure called a clavus. This structure gives the fish its truncated shape.
The sunfish is related to pufferfish and they have a few similarities. The teeth, for example, are fused into a beak-like structure. The fish feed on other fish, squid and crustaceans. It used to be believed that they fed primarily on jellyfish, but it seems that jellyfish only make up a small portion of the sunfishes' diet. As for what eats the adult sunfish, the list is quite small since it is such a large fish. The main predators of the adult sunfish are orcas, sealions, and large sharks.
One of the most intriguing aspects of the Ocean Sunfish is that, in addition to being the largest bony fish alive today, the females are also capable of producing the most eggs at a given time for ANY vertebrate.The females can release up to 300 000 000 eggs at a time. Yes, that is 300 million eggs. The eggs are released by the female and the male then swims over to them and releases his sperm. This means that the eggs are fertilised externally. When the eggs hatch, the little sunfish fry are only about 2.5mm (3/32inch) long. This means that to reach their adult size, the fry have to grow about 60 million times larger, which is one of, if not the most extreme growth of any vertebrate. However, while the growth rate in the wild is unknown, in captivity they can grow extremely quickly. One such youngster from the Monterey Bay Aquarium grew from 26kg to 399kg (57 to 880lbs) in about 15 months. It is not known if this type of growth rate is the same for wild sunfish, and we aren't even sure how long they live in the wild.