SUNFISH

The ocean sunfish vies for the title of strangest fish in the sea. Its Latin name, Mola mola, means millstone. Recorded up to two tons, this gentle giant inhabits all tropical and temperate seas, excluding the icy polar seas. The Ocean Sunfish is found worldwide. In Australia, it has been recorded from Sydney, New South Wales, to Tasmania and west to Mandurah, Western Australia. Ocean Sunfish are usually found in oceanic waters, but occasionally come inshore. Sunfishes are often seen at the surface where they may be mistaken for sharks, because of the large dorsal fin.

The ocean sunfish (Mola mola) is the world’s largest known bony fish (sharks and rays are cartilaginous, not bony). At least one estimate over 3000 lb. has been recorded and individuals reaching 11 ft. (3 m.) from fin tip to fin tip have been seen.

DIET

Mola mola eat a variety of foods, the most common prey items being gelatinous zooplankton like jellyfish, Portuguese man-o-war, ctenophores and salps. Squid, sponges, serpent star bits, eel grass, crustaceans, small fishes and deepwater eel larvae have also been found in M. mola guts indicating that they forage both at the surface, among floating weeds, on the seafloor and into deep water.

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 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.

SIZE, GROWTH and AGE

The average size of an adult Mola mola is 1.8 m (6ft) from snout tip to the end of the "tail" fin and 2.4 m (7 ft 10 in) between the tips of the dorsal and anal fins. The average weight is up to 1 tonne (2200 lbs).

The largest mola ever recorded was 2235 kg (4,927 lbs). It measured 3.1 m (10 ft) from tip to "tail" fin and 4.26 m (14 ft) from dorsal fin to anal fin tip. This animal was a Mola mola and was struck by a boat off Sydney, New South Wales, Australia in September, 1908 (Carwardine, 1995). But see: http://news.nationalgeographic.com
/news/2003/05/0513_030513_sunfish.html.

No data exist on how fast mola grow in the wild but one individual in captivity at the Monterey Bay Aquarium gained 364 kg (800 lbs) in 14 months. Fattened up on a diet of squid, fish and prawns, this fish had to be airlifted out by helicopter and released into the bay after outgrowing its tank.

The longevity of molas in the wild is also a mystery although Kamogawa SeaWorld in Japan has housed the same individual for over 10 years in captivity. We are presently looking into ways of aging molas through a variety of methods.

 

SIGHTINGS and BEHAVIORS
Mola mola are the most commonly encountered sunfishes. Typically they are found sculling like a shark with their dorsal fin flapping out of the water or basking on the sea surface--often in association with a seagull. Molas will actually solicit a seagull’s help in removing external parasites. If however the cleaning gets too rough, the sunfish will simply spit water at its avian assistant and swim out of sight.

Off the California coast, sunfish are frequently found near floating rafts of dislodged kelp called kelp patties. Under these floating oases, sunfish solicit help from cleaner fishes like half-moon Medialuna and senoritas Oxyjulis. Sunfish can also breach, clearing the surface by up to 3 body lengths—presumably as another tactic to dislodge parasites.

 

 

SUBMERSIBLE and ROV SIGHTINGS
While most sightings are at the surface, molas have been sighted in deeper waters with submersibles and remotely operated vehicles. A Mola mola was encountered by Sylvia Earle piloting the 1atm Deep Worker submersible at 500m (1640 ft) in the Dry Tortugas off Florida last summer. Just recently we received an ROV sighting of a Mola mola at 520m in the Gulf of Mexico.

 

Sunfish Rehabilitation Facility at Two Oceans Aqaurium.

Upon arrival at the Aquarium, the sunfish is first treated for its physical injuries as well as for disease and parasites. As soon as possible thereafter, Aquarium staff attempt to feed the sunfish. This is vitally important, as it is the only means whereby antibiotics can be administered. The skin of a sunfish is so thick (up to 5cm thick) and tough that it is impossible to penetrate it with a hypodermic needle. Like all fish, sunfish also have parasites which live either externally (on the skin and in the gills and mouth) or internally (in the gut). External parasites are removed by immersing the fish in a series of freshwater baths. Internal parasites, such as tapeworm and roundworm, are treated with general deworming tablets manufactured for small mammals such as dogs and cats.

Although sunfish have a primitive, almost dinosaur appearance, they respond very quickly and positively to training. They are trained to respond to a variety of stimuli (cues). "One of the major obstacles in keeping sunfish is their tendency to rub against exhibit walls at night whilst resting. We have designed a PVC 'soft chamber' into which the fish will be moved at night. The purpose of the training programme is to enable us to move our display animals to and from the exhibit without any stress at all. To achieve this, we must teach them to enter and leave the 'chamber' at their own free will," explained Dr Garratt.

Before feeding, a bell is rung to indicate that food is on its way. The sunfish is then required to "target" (put its nose) to a coloured disk after which it gets its food. "Once it is accepting food in this manner, we slowly begin to handle it during feeding so that it eventually becomes totally relaxed and learns to trust us." Should these methods prove to be successful, the Two Oceans Aquarium will have solved a dilemma faced by numerous international aquariums and people worldwide will be able to appreciate the extraordinary sunfish from an underwater perspective.