In our New England waters, the most commonly encountered ocean sunfish is the Mola mola, also called the common mola. These large bony fish can be sighted in Cape Cod Bay and Massachusetts Bay in the summer months of July and August. Common molas are often observed lying on their sides at the water’s surface. They seem to be sunning themselves and this behavior has given them the common name of “sunfish”. Molas have been observed in both temperate and tropical waters. Yet their exact distribution and overall movements is not well understood.
The unusual swimming behavior of the common mola often alerts us to the presence of this animal at the water’s surface. As the fish lies on its side, the dorsal fin flops up and down causing a disturbance at the water's surface. This sculling motion can be used to help distinguish the common mola from the basking shark. The basking shark also has a large dorsal fin, but the fin is typically observed erect as it moves slowly along the water’s surface.
The common mola has an unusual body shape as well as unique external features. The body is somewhat flat and rounded giving this fish the appearance of being “all head” and very little tail. This circular, thin body shape is the basis for the Family name, Molidae, which is derived from the Latin word for “millstone”. The skin is silver in coloration and has a slight sheen overall. Although not obvious from a distance, the skin is covered with copious amounts of mucus. The skin is also very thick and has a gritty texture when touched. The animal’s mouth is quite diminished in size and very rounded in appearance. The mouth is formed by the fusion of the animal’s 4 teeth and is used to capture gelatinous organisms, like jellyfish, ctenophores and Portuguese man-o-war. But don’t let this animal’s strange shape and unusual features fool you. Common molas are the heaviest bony fish in the world, reaching lengths of 6 to 10 feet and weights of 2 to 4 tons. However, little is known about their feeding habits and reproduction. Females have been reported to carry the most eggs of any vertebrate. These eggs are minute in size and when they hatch, produce a larvae that is quite comical in appearance. The larvae of the common mola have numerous spines projecting from many directions. As the larvae grow, their spines and the majority of their caudal while the tail fin slowly disappears. Finally, we begin to see a fish that more closely resembles the larger adults.
Many people often refer to the common mola as the “ocean sunfish”. However, there are two other species of sunfish in the family Molidae including the sharp-tailed mola Masturus lanceolatus and the slender mola Ranzania laevis. Although neither species is commonly observed offshore, the sharp-tailed mola have been sighted on a number of occasions in the water’s off New England. Sharp-tailed molas have have a similar appearance to that of the common mola. However, one obvious difference is that sharp-tailed molas have a projection on the tail fin, also called the caudal fin. This projection provides the basis for their common name. When you sight a mola offshore, it is best to photograph the caudal fin in order to verify which species of mola you have observed. The terminology used to distinguish between the three different species can be a bit confusing. In actuality, the words “ocean sunfish” can be applied to all three species of mola. Therefore, it is best to refer to the more commonly sighted Mola mola as the common mola, not the ocean sunfish. Ocean sunfish are not fished commercially in the waters of the United States. However, molas are eaten throughout Asia with Taiwan and Japan being the largest markets.
Each year, a small number of common molas strand, typically dead, on New England beaches. Some animals have visible propellor scars indicating that they have been hit by boats. Others show signs of having been entangled in fishing gear. Other individuals were healthy animals that stranded in shallow tidal areas as the tide went out. A large number of strandings occur each fall and early winter, when ocean sunfish move into shallow tidal areas like harbors and bays. As the tide goes out, these sunfish will become trapped in shallow areas and strand. Later in the winter, any ocean sunfish still in our New England waters will become cold-stunned, a hypothermic response to prolonged cold water temperatures. NECWA staff and interns respond to both live and dead strandings so please call us at 508-566-0009 if you see an animal on the beach.