By now you've all seen the video of local boaters encountering a "sea monstah" (watch the video here on Boston.com—NOTE: the language is vulgar and may not he appropriate for younger viewers). In fact, that large silvery fish is an ocean sunfish, or Mola mola.

A Mola mola as seen on a New England Aquarium Whale Watch (Credit: Boston Harbor Cruises)

Mola mola are no strangers to local waters. Our whale watches have been seeing them all summer. And our researchers in the Bay of Fundy see these large fish regularly.

Credit: New England Aquarium Whale Watch/Boston Harbor Cruises

So what is a Mola mola? These fish are the largest bony fish in the world. An adult can weigh more than 2,000 pounds! They have no real tail, small pectoral fins, and large, extended dorsal and anal fins. They eat mostly jellies and salps and can be found in oceans around the world. While they can dive several hundred feet underwater, they're commonly encountered basking on the surface. Scientists believe this behavior may be way to thermoregulate, or it allows seabirds to pluck off parasites. Our right whale researchers have described these clumsy looking fish as "wobbling, struggling pancake[s] at the surface."

Credit: New England Aquarium Whale Watch/Boston Harbor Cruises

When basking at the surface, a mola's dorsal fin can break the surface of the water. After a few seconds, the fin (and so the fish itself) will lay horizontally against the water until it rises vertically again. That flapping fin can look a lot like a shark fin. Here's a video that can help you distinguish between the fin of a basking shark and that of a Mola mola.


Video: NECWA1 with Massachusetts Division of Marine Fisheries via YouTube

Mola mola pose no threats to human. They are frequently caught as bycatch in fishing nets, and they are vulnerable to eating ocean pollution as plastic bags can often be confused as jellies. Do your part to protect ocean sunfish, sea turtles and other marine animals by using refillable water bottles and recycling or disposing your litter properly.

And here's one last fun fact about Mola mola: One of the Giant Ocean Tank divers has an ocean sunfish tattoo on his leg! See the picture on our Instgram.