Natural La Jolla: Ocean sunfish Mola mola
If you are out boating in local waters, one of the strangest fish you may come across is the ocean sunfish or Mola mola.
These gigantic odd-looking fish are the largest bony fish in the world (whale sharks are larger but have a cartilaginous skeleton). An average mola is 6 feet in length, and up to 10 feet vertically; an average one may weigh up to 2,500 pounds!
They are roundish in shape and compressed from side to side. Their large triangular fins (one dorsal, one anal, set far back on their body) often look like a shark fins when they are swimming upright in the water. The fish itself looks like a swimming head — there isn’t much body behind their tall fins — just a scalloped tail, which is called the clavus. To swim, molas wave their fins back and forth and steer with their clavus.
A few years ago, I found myself snorkeling with three junior molas in the Galapagos Islands, where they seemed to just float up and down in the water column, while keeping curious eyes on us.
Most often they are seen at the water’s surface basking on their sides. While lazing
about at the surface, gulls may help pick off parasites (molas typically have a heavy dose of parasites).
Molas have large eyes that are set back from their tiny mouths. Strangely they cannot close their mouths, and their teeth are formed into a beak-like structure, as is seen in pufferfish (a relative). This beak helps them break down their gelatinous prey, such as jellyfish and squid. Their predators include sea lions, killer whales and sometimes dolphins.
This past summer, the waters off San Diego were especially productive for molas and large groups of juveniles could be seen swimming together.
Usually, you may see a solitary mola or you may find a few within a bigger area. They are one of the most productive fishes in the sea, with a mature female producing some 300 million eggs. Perhaps this past year was an especially good recruitment year for molas.
Ocean sunfish are vulnerable to being caught in some kinds of fishing nets and may mistake plastic bags floating in the water for jellyfish prey, which is why it’s always a good idea to pick up rogue plastic
bags especially when we see them heading for the ocean. Now that California is banning single-use plastic bags (effective in July 2015), there may be less bags lost and floating where molas may pick them up.