Thursday, March 15, 2012

The Heaviest Bony Fish...

Common mola
An Ocean Sunfish, Mola mola, also known as the Common mola.  This fish deserves the title of "heaviest bony fish" because it averages 2,000lbs.  The current record for the largest Common mola is 10ft in length, weighing 4927 lbs.  The term 'mola' means Millstone in Latin.  A millstone is used to grind grain, and this fish relates to one in color and size, thus earning the name Mola mola.  When Common molas hatch out of eggs they resemble floating pincushions, very similar in appearance to puffer fish.  As they age, they lose their spikes and their tales.  From the above picture, it is evident that these fish do not have a caudal fin; instead they contain a “clavus,” which is the fusion of the dorsal and anal fin rays.  Adults also lack swim bladders. 

Ocean Sunfish
These giant fish feed on jellies, specifically the Portuguese Man o' War, and also Ctenophores and Salps.  Because these organisms are not completely nutritious, Ocean Sunfishes will prey on anything they may have to, such as small squids, sponges, other fish and several types of crustaceans.  They may additionally feed on weeds floating among the surface.  When feeding, these fish suck jellies in and out of their mouths until the food is small enough to ingest completely.  A mucous-like lining in their digestive tracts allows Common molas to eat such prey.  Shopping bags littered in the ocean become an extreme danger to these animals.  This is because shopping bags in water resemble jellies, which attract the Common molas.  Once they ingest the bag, there is a possibility of it getting trapped in their throats.  If the bag does not immediately stop in the throat, it could make its way to the stomach and cause a block, which would lead to slow starvation for the fish.  (This is a good reason to reduce your use of plastic shopping bags... go green!) 

The only aquarium in the United States to possess Common molas is the Monterey Bay Aquarium in Monterey California.

 The Common mola also enjoys basking in the sun near the surface of the water.  Mola mola live in tropical and temperate waters of the Atlantic, Pacific and Indian Oceans, along with the Mediterranean Sea.  Two common predators are sea lions and orcas, however they do not have many predators due to their great size.  Nonetheless these creatures still encounter many threats, such as parasites and being caught unintentionally from fishing.  There are nearly forty different kinds of parasites on one Common mola, one specifically being the larval stage of a shark tapeworm.  Around thirty percent of the a swordfish catch in California consists of Common molas, and ninety-three percent of the Spanish gillnet fishery's catch in the Mediterranean Sea is made up of Molas. 


  1. I saw a segment about the removal of parasites from this fish on Blue Planet. They seem very interesting (and funny looking) given the adaptation in their fins but I had no idea they could grow to such a large size!

  2. I do not believe I have every heard of these animals! I might have to go visit the Monterey Bay aquarium in California just to see one of these in person. It is crazy how they lose their spikes and do not have certain fins. This is definitely something new to me and very interesting. Thanks for a great post.

  3. We found a mola hit by a bit while staying on Catalina Island off of Los Angeles and tried nursing it back to health in one of the lab's tanks. But it was not nearly as large as those in your photos - maybe just two feet across.