San Francisco State University Department of Geography
Geography 316: Biogeography
The Biogeography of Ocean Sunfish (Mola mola)
by Lisa Wilkinson, student in Geography 316, Fall 2000
Profile and portrait of the Ocean Sunfish, by author.
Species: Mola mola
Arguably the most eccentric and beautiful looking fishes of the world are the Mola molas. Their appearance is what inspired Carolus Linnaeus to scientifically name them Mola molas. Mola being latin for millstone, is a rounded, flat device used for grinding wheat, a fairly accurate depiction of the fish. Its common name, Ocean Sunfish, originates from its common behavior. It is often seen drifting along with the currents at the surface "basking" under the sun (Love 1991).
Description of Species:
The Mola is a flat, oval shaped fish with a dorsal (top) fin, anal fin (down below), and pectoral fins (on it's sides). While it is in the upright position, these crucial features are what help the Mola swim about as its fins move simultaneously through the water . The tail (if you could call it one) serves more or less as a rudder, guiding the Mola in the intended direction. It's tail is somewhat scalloped and the pectoral fins are fan shaped. The mouth of the Mola mola has been referred to as being snout like and protruding somewhat beyond the mouth area (Barnard 1935). The teeth are fused together and are relatively skilled at sifting and filtering seafood (Johnson 1995).
While the mola is "basking" on its side, it floats along wherever the current will eventually take it (Schwartz; Lindquist 1987).
Although the mola has often been mistaken by anglers as being a White Shark because of its dorsal fin, it seems to be non threatening to divers and often seems friendly to curious onlookers (Johnson, 1995). Their skin is usually a tan gray and is composed of collagen fibers up to six inches thick (Thys 1994), making it a tough victim as prey .
You always felt good about being one out of a million. The Mola is considered to be one of 300,000,000...eggs that is. Whether or not many of these eggs are fertilized is unknown but the numbers are still staggering. The fry (baby fish) are considered to be bathypelagic and are considerably spiny as seen in fig.1. Once mature, the mola's sharp spines will eventually disappear (Stanislav 1971). They grow from being one tenth of an inch (Thys 1994) to a fully matured fish reaching up to 12 feet in length and 14 feet from fin to fin (McCann 1961) As you can imagine some of these Molas can become monsters by their weight alone. Some records show molas weighing over 4,000 pounds (McCann 1961). Breeding is likely to take place in the tropical to subtropical regions of the ocean according to McCann (1961).At 13 degrees south and 146 degrees West in the Pacific Ocean, breeding grounds for the genus Mola have been found, however, more likely than not, breeding grounds are cosmopolitan (McCann 1961).
Figure 1. (Walls 1976)
Unless the Mola is in an aquarium or on display at a museum, its habitat is usually in the epipelagic zone of the Ocean, where the sunlight can still penetrate through the water. The range in habitat depth is anywhere from the surface to 366 meters below (Wheeler 1975). There has been a noted occurrence of a Mola swimming to a depth of 1800 feet in the Bahamas, apparently scrounging for food, but this is believed to be extremely rare (Thys 1994). Molas are most commonly found several miles away from shorelines following drifting kelp forests and have even been spotted loitering by oil platforms according to Love (1991). Unless stranded or dying, molas are usually seen in small groups (McCann 1961). Their food sources consists mostly of jelly fishes, crustaceans, plankton, and comb jellies (Johnson 1995). The hours at which most plankton are near the surface is a good indicator that the mola is a nocturnal feeder. The known behavior of basking during the day could be a means for digesting the last nights meal as many sharks are known to do (McCann 1961).
Mola as a Habitat:
The Mola itself is actually a habitat, for thousands of parasites. Including but not limited to the following parasites... tapeworm larvae (Arru, et al 1994), Remora remora (Castro Pampillon 1996), and Citrobacter freundii (Sato et al 1982). In Matsushima Aquarium in Japan, the molas in captivity were showing physiological signs of sickness. When examined, these molas appeared to be suffering from an invasion of the parasite Citrubacter freundii. Because the molas were exposed to an inflow of parasite laden sea water circulating in the aquarium, chlorine was introduced and the parasites disappeared (Sato et al 1982).
In the open ocean, molas have been sited basking and possibly signaling to seagulls with their pectoral fins to invite them to a feast of parasites. When the seagull finishes, the mola has turned over and the seagull returns for a second helping (Love 1991).
Entry of these parasites is usually via the mouth or the gill region. The gill is covered with a thick skin flap located near the pectoral fin and usually makes it difficult for parasites such as Remoras to enter through.
When molas have been studied after their death, the parasites which very likely caused the death have remained alive for at least 17 hours after the mola was removed from the water (Schwartz and Lindquist 1987).
According to Schwartz and Lindquist (1987), molas have been seen in the Ocean since the Greek and Roman days 1200 B.C.- 400 A.D, but have been there many years before humans records. Russian scientists have found fossil remnants in southwest Russia belonging to the molidae family which date back to the Eocene period approximately 37-58 million years ago. The jaws of these "eomolas" are different in that the teeth are not fused together like they are now but were once separated (Tyler and Bannikov 1992). The relationship between the eomola and the other molids Ranzania, Masturus, and Mola are as follows...a striated bone surface and the general shape similarity (Tyler and Bannikov 1992). Other studies show the evolutionary change resulting from coughing fishes to inflating fishes of the Tetraodontiformes. Most fishes have the ability to cough undesirables after and during a meal, however, fewer tetraodontiformes have developed the successful method of blowing water. The molidae family are in this category of water blowing fishes, able to blow jets of water to search for food such as crustaceans and other bottom dwellers. Beyond this attribute of water blowing evolved the inflating mechanism, which is seen in the molidaes relative the puffer fishes but not among the molidae family itself (Wainwright and Turingan 1997), suggesting divergent evolution between the puffers and the molas. In reference to location and evolution, it is very likley that the mola descended from coral dwelling fish almost 40 million years ago (Stephensen.1994 ). If so, the molas have since expanded this region of origin without much difficulty.
Figure 2. Tetraodontiform Family Tree, by Author. source(Wainwright and Turingan 1997).
The Mola mola is a cosmopolitan fish in that it is found in subtropical, tropical and even temperate oceans, much like the other members of the Molidae family (the Ranzania, and the Masturus) which are also considered cosmopolitan (Wheeler 1975). Although the other species of the genus Mola are considered cosmopolitan, they are less often seen and more likely to dwell in northern hemisphere tropics (McCann 1961). As evident in the distribution map in fig.3, the Mola has been sighted in the ocean near every continent (excluding Antarctica). Many of the sightings of molas have mentioned the finding as a rare occurance such as the Arabian Sea. The Ocean Sunfish has been noted in Australia, India, Ireland, the Meditteranean and the U.S. to name a few. Although it is uncommon to find this fish in the colder temperate oceans, it has been found swimming near Alaska and British Columbia. The only thing restricting the mola from higher latitudes is the coldness of the water. Although Mediterranean climates have cool ocean temperatures, such as the California, Canary and Australian currents, it nevertheless is still a livable environment for this fish.
Map of Distribution:
Figure 3. Mola mola distribution (not limited to the specified areas). Map by Author, National Geographic Basemap.
Are they yummy?:
One factor that the mola can appreciate is that it is not highly demanded in the food market. For some reason the thousands of parasites that it hosts does not appeal to human appetites. Although it has been known to sell in Japan, the demand is not great (McCann 1961). Unfortunately molas are occasionally caught in fishing nets. In 1992, one Spanish drift net fleet in particular caught several molas comprising of 71% of their total catch, though their target was for swordfish (Silvani; Gazo 1999). Not only does the mola need to swim from fishnets but also from white sharks. A mola was found in the belly of one great white shark and the evidence came as three torn remnants (Fergusson et al, 1999). Although white sharks are generalist feeders, it does not seem to have a history of preying on molas (Fergusson et al, 1999). Maybe it was mistaken for a surfboard.
Because the mola is closely related to the poisonous puffer fish, questions may arise on whether the mola or other tetraodontiformes are poisonous. Tests show that neither the mola, or many other tetraodontiformes have high enough levels of toxicity like that of a spiny puffer fish (Saito et al. 1991).
As for nutrients, the mola is of high quality protein containing a majority of the essential amino acids. The fat content is relatively low, and only half of the molas body weight is water (Ara et al. 1994).
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