The Mola mola has fascinated people from the moment they first set eyes on one. Despite this, not very much is known about them. They remain semi mysterious creatures of the sea, always visible and eager to show off, yet keeping many of their secrets well hidden.

These animals have been given many names over the years; the most common bring ocean sunfish, mola or simply sunfish. These can be a little misleading though, as people often use the names interchangeably, sometimes referring to all types of mola or even to the small freshwater sunfish which have nothing at all in common with the Mola mola. Mola comes from the Latin word for millstone – presumably applied to the fish due to its round shape. It works like this:

Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Actinopterygii
Order: Tetraodoniformes
Family: Molidae
Genus + Species: Mola mola (that’s our guy – we’ll just call him mola for short), Masturus lanceolatus (Sharp-tailed mola), Ranzania laevis (Slender mola), Mola ramsayi (Southern Ocean Sunfish)


Swimming head

Schwimmender kopf – that’s 'swimming head' to us – is the name the Germans have given to the mola. If you were to see one, you’d see just how fitting the name is. The mola is shaped rather like a slightly distorted disc. Looking at it from the side it would seem like a huge, kinda elongated circle, and from the front pretty much all you would see is mouth – they are as flat as a pancake.

The shape of the body combined with its rather unusual arrangement of fins make the fish appear as though it was a normal fish that had been cut in half just behind the fins. On the top of their bodies, right at the back, they have a very large dorsal fin which is often mistaken for a shark fin when they swim near the surface. Directly opposite on the underside of their bodies is an equally sized anal fin. Molas to do not have a caudal (tail) fin like most fish, instead the dorsal and anal fin extend downwards and upwards respectively to form a clavus. This is a broadly rounded but very short and firm extension which marks the end of the fish’s body. Molas swim by flapping their dorsal and anal fins in unison to move themselves forward, while using the clavus much like a rudder. Very small pectoral fins wave continuously and appear to act as stabilizers.

Molas can be found in any shade of white, grey and silver with the fins being a darker colour than the body. They often have a shiny, pearlescent look to them and exhibit an endless variety of spots and mottled patches of colour. Also unlike most fish, molas are not covered in scales. Their skin is very gritty – almost like sandpaper - and very tough and leathery, so thick over most parts of the body that hunters often have trouble piercing the skin with their weapons. It is also covered in a thick layer of mucous which is thought to help protect them from infection. Despite this, molas are renowned for the abundance of parasitic life which can be found on their skin. Specimens with over 40 different types of parasite living together are not an uncommon find.

One of the most amazing things about molas is their size – they are the world’s largest bony fish. The average size for an adult specimen is 1.8 m (6ft) from snout to clavus and an enormous 2.4 m from the tip of the dorsal fin to the tip of the anal fin. All together this brings these fish in at an average weight of 1 tonne! The largest mola ever recorded weighed in at 2235kg (almost 5000 pounds) and was 3.1 meters tall and 4.26 meters long.


What an effort

Being so large, molas have to consume a lot of food to survive, however they are far from being veracious predators. Their mouths are really rather small in comparison with the rest of their body, with just a little snout protruding from their face. They don’t have big sharp teeth either; instead they have a hard bony plate on the top and bottom of the jaw which acts a lot like a beak.

Basically, they just swim along with their mouths open and eat whatever happens to get sucked in. They then grind up the prey and spit it out again, repeating this process until the pieces are small enough to swallow and digest. Usually this results in a diet of gelatinous zooplankton like jellyfish, Portuguese man-of-war, ctenophores and salps. But since the mola is so unusual in every other way, so it is with feeding. Rather than just sticking to this surface and shallow water feeding, the mola can dive to depths of 500 meters and so it often gets a meal consisting of squid, small fish, deepwater eel larvae and crustaceans. Although it is not known for certain, it’s suspected that they also forage on the seafloor as specimens have been found with sponges, eel grass and starfish in their stomachs.


Makin’ little ones

One of the biggest unknowns about molas regards their mating habits. We do know that the females produce more eggs than any other vertebrate. Females have been found containing as many as 3 million eggs in their ovaries. The eggs are very small, about the size of a little 'o'. It is thought that the females release the eggs into open water, after which the male swims over the area and releases sperm to fertilize the eggs. From then on the parents have nothing to do with them and they are left to hatch on their own.

When the eggs hatch, the larvae are tiny – about 1.8mm in size - and do not resemble the shape or structure of the adults at all. They have a primordial tail fin as well as large pectoral fins. But most peculiarly they are also covered in many large spines, very much resembling the puffer fish to which they are related. As the larvae grow, the spines begin to disappear and the bony beak and clavus begin to develop. By the time it reaches about 40mm in size it looks just like its parents did, only smaller.


The life and times…

Molas are found in all temperate and tropical oceans and need a warm environment to survive. Much as with their eating habits, molas often appear to be lazy with regards to swimming. It is common to find whole shoals being carried along by currents, even if this sometimes leads them into colder water where they perish if they cannot swim back to warmer waters fast enough. Its shape may make it look like its all head and no body, but there isn’t a whole lot up there. Their tiny brain, about the size of a walnut and weighing only a couple of grams, is attached to a spinal cord just a few inches long.

The behaviour of molas is something that has long fascinated researches because no one seems to be able to explain it. The molas got their nickname of sunfish due to their habit of basking in the sunlight and sightings are common because of this. The fish turn over onto their sides and lie like that on the surface of the water. Sometimes it will just be one of them, sometimes a whole group, sometimes for a few minutes, other times for whole days.

Many theories have been put forward to explain this, the most popular being that it has to do with heat regulation. Since the molas can dive so deep, it is hypothesised that perhaps after such expeditions they simply like to lie in the sun and soak up the heat. Others say that because of the shape of the molar and the arrangement of its eyes, it cannot normally see in very many directions when swimming. When it turns sideways and lies like that it allows it a much larger view of below, helping it to spot prey or predators. Yet others claim it is a sign of illness and that the fish do it when they are sick or dying.

Another common behaviour is for large groups of molas to collect in one area. Like one big get-together the fish just mingle near the surface for days, with comings and goings all the time. Since these gatherings often take place near patches of drift kelp, it is thought that they may be parasite clean-up times. Perhaps the molas get help with removing some of their large array of pests both from each other and the other small fish that live in the kelp. The molas can also be seen jumping as much as 10ft into the air and landing back in the water with a resounding splash. This could also help to rid them of parasites or it may be a show for potential mates.


A sad demise

During late summer and autumn, shoals of molas tend to stay very close to shore. This results in lots of problems with incidental bycatching from fishing boats. California’s drift gillnet fisheries can find that as much as 25% of their total catch is made up of mola. In the Mediterranean it is even worse, during the 90's driftnet swordfish fishery off the coast of Spain would produce bycatch rates of up to 90%. Since these fish are only served as a rare delicacy in some parts of Asia, most of them simply die a pointless death. The global population of mola is not known, so it is hard for scientists to say how badly this affects the species.

Due to their very large size, molas do not have very many natural predators. A molas primary worry would be an attack from a sea lion. One of the main points of documentation of this comes from observations off the shore of Monterey, California. When the molas gather here in the autumn one can be sure that the sea lions are not far behind.

The sea lions viciously attack molas near the surface, ripping off their dorsal and anal fins. Without these, the fish is left helpless and the sea lions begin phase two. They dive underwater and then propel themselves toward the mola on the surface at great speed. Connecting their head with the molas body, they punch it out of the water and then let it fall. They can repeat this for hours, and it’s thought to be a way of softening and puncturing the tough skin so that the sea lions can get to the soft meat inside. But often it appears to be done just for the fun of it and a mola will be 'played with' for a few minutes and then left before it is dead. Without its fins it is unable to swim and simply sinks to the floor where it is slowly eaten by star fish and other small animals.

No one knows how long molas live for in the wild. Some suspect that like other large sea animals they can live for many many years. The oldest one in captivity is kept at Kamogawa SeaWorld in Japan; it’s been living there for 10 years.


The future

Although molas are very friendly to humans in the water, and often a little too inquisitive, we can’t ask them what’s up and they do not adapt well to life in captivity. Thus it seems that we may never know exactly why they do what they do. Yet in recent years there have been many programs using tag and release, satellite tracking and attempted controlled breeding to learn more about them.

Organizations such as oceansunfish.org and The National Geographic Society are in the midst of decade long studies to try and establish baseline biological data for the species. This will help us to learn how and where they breed, how far they migrate and what relationships they have with other sea animals. But for now, we can simply marvel at their huge size and gentle nature and wonder what surprises they hold in store for us.


These amazing animals really need to be seen to be believed, you can look here for some great pictures.


Sources:

  1. OceanSunfish.org: http://www.oceansunfish.org/sightings.html
  2. fishbase.org – Mola mola: http://www.fishbase.org/Summary/SpeciesSummary.cfm?ID=1732&genusname=Mola&speciesname=mola
  3. Larval Ocean Sunfish - Mola mola (Linnaeus, 1758). Found online at: http://www.amonline.net.au/fishes/fishfacts/fish/molalav.htm
  4. Fine-scale movement patterns of the ocean sunfish, Mola mola, off the coast of southern California, as determined by acoustic telemetry. By D. Cartamil & C. Lowe. Found online at: http://www.csulb.edu/web/labs/sharklab/students/current/dan/flash/projectmola.html
  5. Austraila Museum Fish Site: http://www.amonline.net.au/fishes/fishfacts/fish/mola.htm
  6. The Ocean Sunfish by Enrique Rodríguez. Found online at: http://marenostrum.org/vidamarina/animalia/peces/mediterraneo/mmola/indexi.htm
  7. Ocean Sunfish Photographs by Phillip Colla. Found online at: http://www.oceanlight.com/html/mola_mola.html

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