Floating "Millstones" In The Ocean
At first glance, these curious-looking fish look like gigantic fish heads without a body. They are known as “sunfish” in English and “mondfisch” in German. Although the two names are indeed descriptive, the fish's scientific name – Molidae, which comes from the Latin word mola (meaning “millstone”) – perhaps best describes their unique body shape.
Seeing a sunfish up close is a unique experience. The animal has a large head with one fin each on the top and bottom of its massive body. It has no scales, but a thick leathery skin that is several centimetres thick. Its body comprises a gelatinous mass of cartilage (no bones!). Additionally, it is a teleost (ray-finned fish).
Sunfish do not have a swim bladder, an organ which in other animals would give controlled bouyancy. However, the sunfish has no need for it, as its body tissues has a density of 1.03g/cm3, similar to that of seawater. This allows the fish to maintain its bouyancy despite swimming to increasing depths.
Info on Sunfish
German: Mondfisch (Moonfish)
Best-known representative species: mola mola
Size: Up to more than 9 feet high and almost as long
Weight: Up to 2 tons
Habitat: Offshore resident that sometimes stops by at the coast
Where to find: Worldwide in warm seas
Triple world champion?
2.3 tonnes: The heaviest recorded sunfish specimen topped the scales at 2.3 tonnes as the world's heaviest bony fish (Teleostei – yes, indeed - no bones but belongs to the family of teleosts).
300 million eggs: When the female spawns, at least 300 million eggs are released. However, there's no need to worry about our seas overflowing with sunfish – most of the eggs and larvae end up in the stomachs of other fish.
0.25cm to metres-long adult fish: That's how much "growing" the 0.25cm larvae will do, as it grows into adulthood. Its weight gain is just as impressive: In just 15 months, a sunfish managed to gain 373kg while in captivity. That works out to 0.82kg per day!
Limited funds have been set aside for the sunfish, as they do not have any commercial interest. However, with its fins above and below its body, the sunfish's movements have become quite efficient, as shown by experiments in the flow channel. The GPS system has also tracked the sunfish worldwide, confirming that covering distances of 2,000 kilometres in three months is not uncommon for the sunfish.
Posted by National Geographic Channel on Freitag, 28. August 2015
Sometimes, sunfish lie flat on the seabed, as if they are basking. So far, we have not found out why they do this; one theory suggests that sunlight and UV radiation may help to expel parasites (though this has not been confirmed). In the open seas, there are no cleaning stations. Thus, to get rid of parasites, the sunfish sometimes leap into the air, and then turn their bodies horizontally so they crash back onto the ocean surface with a big splash, much like how whales remove the parasites from their bodies.