Mola mola is more commonly known as the ocean sunfish. This unusual looking fish is found in the Pacific, Indian, and Atlantic Oceans, as well as the Mediterranean in waters that are in the tropical to temperate range. Though usually found in open water, they will go into more shallow waters to make use of cleaner fishes. They are actually the largest of the bony fish, coming in at up to nearly 5000 pounds and over ten feet in length. Another unusual trait, this fish is scaleless and has rubbery, thick skin. Its body is flattened laterally.
The sunfish is also odd in its method of propulsion. While most fish use their caudal (tail) fin as their main means of propulsion, this species doesn't even have a caudal fin. It instead has what is called a "clavus" which it uses as more of a rudder. The dorsal and anal fins are enlarged,and are used to propel them using a sort of flapping motion. They will sometimes be seen swimming on their sides, and this form of propulsion makes this feat easier. They are known to undergo vertical migration, likely to follow their planktonic prey. The mola mola can sometimes be found basking at the surface of the water, which is believed to be a way for them to warm up after diving to deeper, colder water.
|A mola mola caught in 1910|
A lot is still unknown about this species.
Here is a video of this fascinating creature:
Source is Animal Diversity Web. Images are from Wikimedia commons and are copyright free: one, two.