Sunday, October 2, 2011

Mola mola (Ocean Sunfish)

Ocean sunfish or mola mola lying on its side, just under the
surface.  The head it toward the top right corner. 

Ocean Sunfish or mola mola are the largest bony fish reaching up to 3.3m (11 feet) and the heaviest over 2300 kg (5000 lbs).  They are disc shaped with two large fins, the dorsal and anal fins which they use to propel themselves through the water.  They are flattened vertically.  Their tail is a long, wavy structure.  They feed on jellies, comb jellies and other plankton.  They come to the surface and often lay on their sides giving them their name, ocean sunfish.  The French name is actually moon fish, poisson lune.  The surface behaviour has been suggested as a method to warm their bodies after spending time as deep as 600m.  Frequently those observed in the Bay of Fundy have their mouths open so perhaps they are also feeding close to the surface.  Most years we see only the occasional ocean sunfish but in the last two summers, multiple sunfish have been seen some days.  The ocean sunfish this year also seem much larger than the ones seen in other years.  Why have the numbers increased in recent years?  It is unknown but some years warm-core eddies break off from the Gulf Stream and get swept into the Gulf of Maine and Bay of Fundy carrying with it species that are usually seen in warmer waters.  This could be the case or other forces were in play bringing these huge fish into the Bay.

Ocean sunfish or mola mola lying on its side at the surface.
Its mouth is open.  These fish feed on jellies.
They are slow moving but can manoeuvre out of the way of oncoming vessels if the vessels aren't travelling quickly but are at risk when they are at or just below the surface since they are difficult to spot until nearly on top of them. They can also breach or leap out of the water. Inshore, however, their ability to navigate leaves much to be desired. 

On the evening of September 10, two friends of the GMWSRS out for a drive had stopped at the fishermen's wharf and found a stranded ocean sunfish.  It was up against the wharf and was bumping into boats, piers and the shoreline.  They tracked us down and we rallied a few people to help, some of whom had never seen an ocean sunfish.  We tried to herd it out from between the floating wharf and the fishermen's wharf using a small inflatable and oars but to no avail.  The sunfish would not go back under or between boats or piers.  It was difficult to judge how heavy this sunfish was but it was at least 2 m across, not including the fins, the same size as the inflatable. We were quite concerned because the tide was beginning to recede and we didn't want the fish to completely strand. 

Finally we decided to grab the sunfish by its dorsal fin when it was up against the shore and try to tow it out.  A friend, who is also a whale watch captain, and the fellow who spotted the sunfish got into a much larger, motorized inflatable and were able to get the sunfish away from between the wharf and the floating wharf but lost their grip before they could get it around the end of the wharf. The fish blundered into a row of boats tied to the wharf before they could grab it again.  It was amazing to watch the sunfish try to swim away from them, jetting water out through its gills as a type of jet propulsion to increase its speed.

Pectoral fin of an ocean sunfish as it lays at the surface.
The second time they got the fish to the end of the wharf but they again lost their grip and the fish got away, this time heading off through the boat moorings but away from the wharf.  It was not seen again and, hopefully, headed out to deeper water with fewer obstacles.  The rescuers did not go unscathed because sunfish skin is like sandpaper, cover by a mucus layer, and they had several scrapes on their hands and arms.  Gloves would definitely be in order next time.

Here are some other articles about stranded sunfish this summer, the outcomes deadly for the sunfish, despite valiant efforts:


  1. A really interesting animal with it's unusual shape. By the way : It`s name in german is "Moonfish" !
    Bye !

  2. I guys,

    Check mola mola (the ocean sunfish) page at,
    a comprehensive catalogue of marine species to sea lovers.