Join me in the cold, dark, life-sustaining NE Pacific Ocean to discover the great beauty, mystery and fragility hidden there.

Holy Mola!

Chad Chrighton, the pilot who found the Mola mola near the seaplane base. Photo credit: Mike D’Amour (North Island Gazette).

Something very unexpected landed near the Port Hardy seaplane base on October 20th – a dead Mola mola. This is the largest of the world’s ocean sunfishes and looks like a cartoon character rather than a relatively fast-moving, deep-diving fish whose design has been perfected by millions of years of evolution.

This fish species is aptly named since Mola means “millstone” in Latin and indeed this fish looks like a huge, flat, gray circle and has rough skin.  It appears to have no body, only a giant, round, flat head with a small beak-like mouth. It is propelled by two pointy fins (dorsal and anal) and is steered by a wide, rounded, rudder-like tail. 

Photo credit: Erika Grebeldinger.

Mola molas are found in all temperate and tropical seas and are relatively common in the open ocean off our coast; often getting misidentified as sharks. They were believed to be passive drifters who travelled only at the surface, wherever the current took them. However, satellite tracking studies have revealed that they dive deeper than 600 m and travel an average of 10 to 20 km per day, the same distance traveled by open-ocean shark species. 

Matthew Drake measuring the Mola mola. To give you get a sense of size, Matthew is almost 2 m tall (6.5′).

They are certainly a rarity on the inside of Vancouver Island however and I greatly appreciate that Matthew Drake let me know about this find and that he undertook a necropsy of the giant together with Louisa Clarke and Natasha Dickinson. (I only recall there being a similarly sized one on the beach in Port Hardy in 2005). 

This Mola mola measured 2.00 m wide, from beak to tail fin, and 2.06 m long, from the tip of one pointy fin to the other. It may have weighed more than 200 kg. Remarkably, this is small for its kind. Mola molas hold the record for being the largest bony fish on earth with an average mass of 1 tonne. The largest Mola molaever recorded was 2,235 kg and 3.10 m by 4.26 m (it was struck by a boat near Australia in the early 1900s). Note that the whale shark can be more than 9 times bigger than this but, it is not a bony fish. 

Mouthparts. Photo credit: Mandy Norrish.

Matt and the team concluded that the Port Hardy Mola mola was female which meant that she could have up to 300 million eggs in her one ovary. This is another record for the species: having more eggs than any other animal with a backbone.  Another astounding fact is that the larvae could grow to be 60 million times their weight at hatching.

The investigation also revealed partially digested jellyfish in her gut, which is the typical prey of Mola molas. Their diet also includes small fish, eelgrass and crustaceans and they are able to spit out and pull in water and food with their unique mouthparts. As with all species that feed on jellies, a conservation concern is that they mistake plastic bags for their food. However, there was no evidence for this being the cause of death for this particular Mola mola.  

Maybe parasites were a factor in her death? The team found lots of skin and intestinal parasites! Some of the round worms in the guts were even still alive. Parasites are common for Mola molas. In fact, it is now believed that the behaviour of “sunning” at the surface (hence, ocean “sunfish”) might be so that birds can feed on the skin parasites and that jumping more than 3 m out of the water might help dislodge some parasites too. Mola molas are also found associated with drifting kelp patches, where small fish can clean away the pests.  

HOLY MOLA you never know what you are going to find in our amazing marine backyard. 

All the information collected will be reported to oceansunfish.org and the mouth parts will end up on display in Telegraph Cove’s Whale Interpretive Centre. 

 

Beware!  Fabulous Mola mola parasite pictures below! 

Advance only if you are NOT about to eat lunch and/or if you a biology-type like me who can view these kinds of photos in rapturous fascination anytime!

Sources: 

Her intestines were an astounding mass of worms. Likely the species include the parasitic flatworm, Nematobibothrioides histoidii which is thread-like but can grow to be over 12 m (40′). No one apparently knows just how long they can become, in part because dissections/necropsies on Mola mola are rare events. Photo credit: Natasha Dickinson. Click image to enlarge.

Parasites near the eye. Photo credit: Mandy Norrish. Click image to enlarge.

More great ectoparasites. Photo credit: Matthew Drake. Click image to enlarge.

Her single ovary. Can have 300 million eggs. Photo credit: Natasha Dickinson. Click image to enlarge.


5 Responses to “Holy Mola!”

  1. Anonymous

    is it possible to infect the local fish with the parasites that are floating in the water were the fish was gutted?

    Reply
    • jackiehildering

      REALLY interesting question revealing a deep concern for the environment. The vectors the allowed the Mola mola to get the parasites would already have been present in the marine environment. These parasites are naturally occurring and the Mola mola is not rare to our Coast. Please let me know if you want a more in-depth answer.
      The intestinal parasites were also not left on shore but bagged up and taken away in case of interest to research.

      Reply
  2. Anonymous

    I believe the width & length measurements are transposed in your article

    Reply
      • Anonymous

        Thanks Jackie…we did not get to see this phenomenon, but I sure was interested in the photos…just after lunch, too!!!!!, good thing. Thanks for keeping
        in contact…BJ

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