Mola mola (Common mola)

The most common and widespread of ocean sunfish in the northern hemisphere is Mola mola. These fish, like all ocean sunfishes, appear as if their bodies have been somehow truncated leaving them little more than a large head punctuated with set of long dorsal and anal fins sweeping it along like a pair of vertical parentheses. The body is less than twice as long as it is deep.

Mola mola have a rounded tail when they are juveniles which can become scalloped as they age and become larger. Their scales are multi-cusped and jagged making their skin very gritty like rough sandpaper. They are covered with copious amounts of mucus and typically silvery in color with a slight opalescent sheen although their skin can exhibit strikingly changeable, light and dark spotty patterns. Their clavus is supported by 8-9 ossicles and these ossicles are narrower than the space between them.

Mola alexandrini (bump-head mola)

Mola alexandrini is similar to Mola mola particularly in its juvenile stages but diverges as it matures by retaining a rounded clavus. (M. mola develops a wavy clavus in its largest size.) Their rounded clavus (pseudo-tail section) is supported by 14-24 (average 17) fin rays and 8-15 (average 12) ossicles, an enlarged bulbous head, chin bump and rectangular scales.

Mola ramsayi (Short ocean sunfish)

Etsuro et al 2017 suggests that Mola ramsayi be replaced by Mola alexandrini (see characteristics above). Mola ramsayi, commonly known as the short or southern ocean sunfish, has been recorded in numerous locations in the northern hemisphere. Investigations continue to see if Mola ramsayi should be fully retired as there remains some inconsistencies in some descriptions as well as numerous individuals that have a bump head and a wavy clavus—a mix of characters from the Mola mola and Mola alexandrini/Mola ramsayi.

Mola tecta (hoodwinker sunfish)

Mola tecta reside in the southern hemisphere, with records from South America, Australasian waters and New Zealand. They have rounded scales and a distinct bad in the center of their clavus.

Masturus lanceolatus (Sharp-tailed mola)

Masturus can also reach great sizes. As their common name implies, sharp-tailed mola have a bit more to their tail than Mola mola. Similarly colored to Mola mola, they have smoother skin and produce less mucus. Interestingly, sharp-tailed molas are not consummate sunbathers and carry a smaller parasite load than Mola mola and also have a more tropical distribution.

Ranzania laevis (Slender mola, dwarf mola)

Unlike other molas, the slender mola only reaches approx. 100 cm in total length. They are the most colorful and elusive of the ocean sunfishes. They have a smooth, thinner skin than any of the other molas and a vertically oriented mouth.
The Polynesians called these sunfish "King of the Mackerels". It was seen as bad luck to catch and kill Ranzania for such an act would render the mackerel incapable of finding their way to the islands. While this is currently the only accepted species in the cosmopolitan genus Ranzania it is very likely that there are more species waiting to be formally described.

A NOTE ABOUT NAMES

The common name "sunfish" is used to describe the marine family, Molidae, as well as the freshwater family, Centrarchidae. The common names "ocean sunfish" and "mola" refer only to the family Molidae and can be applied all three Molidae species.

The word mola comes from Latin and means millstone–in reference to these fishes’ roundish shape. The common name "ocean sunfish" comes from their habit of lying atop the surface of the ocean appearing to sunbathe.

DISTRIBUTION, MOVEMENTS and RANGES

All species of sunfish are found in all tropical and temperate ocean basins.

While there is considerable overlap, there do appear to be specific preferences depending on species.

With insight gleaned from satellite tagging studies, ultrasonic tagging and our internet sighting form, we are starting to piece together the seasonal distribution of ocean sunfish populations throughout the world ocean. For example Mola mola in the Western Pacific off Japan, were recorded moving from Kamogawa Japan northwards to the Kuril Islands off Russia (Dewar et al. 2010) during the summer months. In Indonesia sunfish tagged in Bali were found to move eastward along frontal margins during the wet season (Thys et al. 2015). In the Eastern Pacific, individuals tagged in Central and Southern California migrate as far south as Baja California during the fall and winter months (Thys et al. 2016). In the Western Atlantic, individuals tagged off Nantucket and Florida in the summer months moved into the Gulf of Mexico (Potter et al. 2011; Potter & Howell 2010) while in the Eastern Atlantic, sunfish tagged off the UK moved south to Spain to the Gulf of Cadiz (Souza et al 2017; others). Sunfish off South Africa move offshore but don't exhibit substantial latitudinal migrations (Hays et al. 2009).

The northernmost record is from 70∘ 44′ N off northern Norway dating back to December 1881 (see Frafjord et al 2017 for more details)

Lepeoptheirus sp. or Caligus sp .
Click for detail. Can you count them all? Photo courtesty Chris Potgieter
Sept 30,2007 at Crystal Bay, Lebongang, Bali Dive depth was 45m at the cleaning station.

Parasitic copepod (Pennella filosa)

Didymozoid trematode
Removed from the inside of a Masturus lanceolatus in Hua Lien Taiwan--supposedly 1 in 100 Masturus there have these tumors.

PARASITES

Since parasites often sport multiple hosts, they can offer valuable insight into ocean sunfish interspecies associations. For instance, one sunfish parasite is the larval stage of a shark tapeworm so at some point the mola most likely falls prey to shark thus enabling this parasite to complete its lifecycle. For a list of known parasites of the family Molidae click here

The common sunfish, Mola mola, is infamous for its impressive parasitic load. Some 40 different genera of parasites have been recorded on this species alone. In fact, even their parasites have parasites–a fact reminiscent of Jonathan Swift’s quip:

So, naturalists observe, a flea
Has smaller fleas that on him prey;
And these have smaller still to bite ’em;
And so proceed ad infinitum

Masturus lanceolatus are not as heavily parasitized as Mola mola. And while they dive to great depths (Seitz et al XXX), they do not appear to engage in sunbathing to the same degree. Little is known about the parasites of Ranzania, the slender mola

Mola mola skin 88x

Mola mola scales 176x

Sea lions (Zalophus californianus)

Bat stars (Asterina miniata) consuming dead sunfish

PREDATORS

There's safety in great size for the ocean sunfishes but on the road to largess, they are open to many dangers. Bycatch through fishing certainly takes a toll on mola populations. And parasites presumably claim quite a few lives as well. Other predators include orcas (Gladstone, 1988) and sea lions.

During the fall months in Monterey, California, sea lions can be seen ripping the fins off sunfish and slamming the dismembered bodies against the sea surface. Presumably this action helps the lions tear through the molas’ skin which is leathery tough and several centimeters thick in places. However, after tossing the bodies through the air for several minutes, the lions often simply abandon their prey. Tragically the hapless, finless molas unceremoniously sink to the seafloor and are consumed slowly by bat stars.

Little is known about predation on Ranzania. However an adult female (335 mm in total length) was found in the stomach of a marlin off Hawaii. Numerous Ranzania youngsters have also been found in the guts of mahi mahi Coryphaena hippurus. (Sherman, 1961)