Ocean Sunfish

Ocean Sunfish Mola mola 

Ocean Sunfish with Great Shearwater

On July 7 a group of 35 naturalists were treated to a good viewing of an Ocean Sunfish (Mola mola) while on a long boat trip off Grand Manan to the Prong area between Grand Manan, NB and Nova Scotia.  The Mola mola is a slow-moving creature so we had a good view and photo opportunity.  Shown above is what it looked like as it moved along slowly at the surface.  There were many seabirds present and the photo shows a Great Shearwater.

Ocean Sunfish (Mola mola)

The Mola mola is a very large pelagic bony fish which inhabits all the world oceans except the Arctic and Antarctic Oceans.  It is a member of the Molidae family which contains the world's largest bony fishes.  There are several species of Molas in this family.  The Molas are prehistoric creatures being around since 45 million years ago.  They are harmless, slow-moving creatures which occasionally occur in our waters.  The Molidae contains fishes which weigh from 247 to 1000 kg or more.  Some rays and sharks can be larger but they are cartilaginous fishes.  

Ocean Sunfish (Mola mola)

The Ocean Sunfish occupies a unique place in the ocean ecosystem.  It drifts around slowly looking for jelly fish, its main diet.  Its top speed is 3.2 km/hour.  Its name, 'mola', is derived from the word for millstone and describes its peculiar shape.  It looks like a fish without a tail; a fish that has only a head.  In German it is called a 'swimming head'.  It is flattened dorsoventrally and its dorsal and anal fins have evolved into large paddles which it uses to slowly move along.  It kind of looks like a lollipop with 2 fins on the lower edges.  It moves through the water by slowly undulating back and forth propelling itself along with the 'paddles'.  

Ocean Sunfish (Mola mola)

The Mola can get very large, 10 ft by 14 feet.  Because of its large size it does not have many predators except orcas, sharks and sea lions.  It is silvery in colour and is covered with tough, leathery, sandpaper-like skin.  The skin is composed of millions of minuscule bony plates each with a tiny spine.  It has large eyes and an open mouth which gives it a weird expression.  It cannot close its mouth and its teeth are fused into a beak-like structure.  Its only mammal-like bones are in the dense bony spine.  The other bones are cartilaginous.  This is an advantage for weight reduction while maintaining structural integrity.  Its intestinal walls are thick in order to resist the stings and abrasions from its food.  Its 'tail fin' is not actually derived from a tail at all but has evolved from a fusion of the trailing edges of its dorsal and anal fins.  It is called a 'clavus' and is used for steering.  

Ocean Sunfish (Mola mola)

The dorsal fin which is frequently out of the water looks much like that of a shark.  It can be distinguished by the motion of being waved in and out of the water as it propels the fish along.  The dorsal fin of a shark would be cutting straight through the water.  See the photo above.

The Ocean Sunfish eats mainly jelly fish but also small fish, zooplankton and algae.  It dives to a depth of 500 ft to feed and then returns to the surface to warm itself after being in the cold ocean depths.  That is how its gets its name, 'sunfish'.  Its skin can be covered with parasites and it often has commensal fish feeding off these parasites.  The Sunfishes sometimes breech in an attempt to rid themselves of these parasites with the force of the heavy splash.  The female lays 300 million eggs and the young are only millimetres in size when they hatch.  The young travel in schools but become loners when they reach adulthood.

Ocean Sunfish (Mola mola)

The Mola mola has a very large eye which can be seen in the photo above.  They are curious creatures and often approach people.  It seemed to be enjoying watching us as we watched it.

The populations of Molas are vulnerable to human activity.  Many get caught in gill nets and other fishing gear.  They are especially vulnerable to the garbage in our oceans.  Many suffocate on plastic bags which they may mistake for jellyfish.  They also consume other ocean trash like so many other species.  

We must clean up our oceans in order to protect vital ocean ecosystems!