Mola Molas

With specimens weighing nearly 5,000 pounds, Mola molas, also known as ocean sunfish (or just molas), are the heaviest bony fish in the world. Only in the last 20 years have divers and photographers begun to get quality encounters with these compellingly weird creatures. Found in tropical and temperate waters around the globe, they are actually fairly common animals. There were relatively few still or video images of Mola molas until the early- to mid-1980s, and encounters underwater were considered quite rare. But there are more divers with cameras today and more divers exploring the places where molas are found.

Although divers encounter these fish in the Azores, the Mediterranean and even Florida, two of the best spots for mola encounters are the open sea off the California coast and the reef drop-offs of Bali. The outer edges of kelp forests, elevated parts of the seafloor and reef drop-offs are features that commonly draw these pelagic animals closer to shore.

Mola molas are drawn to near-shore areas mainly by cleaning stations, where reef fish help rid them of bothersome parasites. Molas carry loads of parasites, both internally and externally. Large, stringy parasitic copepods can be seen attached to many molas. The fish are often found basking on the sea surface, exposing their flat sides to seagulls for cleaning — hence their common name: ocean sunfish. Even divers assist the occasional cooperative mola by pulling off a parasite or two.

The cornerstone of the mola's diet is jellyfish and other gelatinous zooplankton. When it finds food, the fish uses its relatively tiny mouth, which is filled with bony plates, to crush it before swallowing. Mola molas grow very quickly — one captive individual gained 880 pounds in just 14 months and had to be removed from its aquarium by helicopter. Of course, that one was fattened up on squid and fish. The amount of nutritionally poor salps and jellyfish required for a 1,000-pound fish to maintain its weight in the wild is extraordinary. It's rare to observe molas actively feeding in the wild, but during population explosions of tiny jellies called "by-the-wind sailors" (Velella velella), the fish can be seen on the ocean surface slurping them down with vigor.

Molas have a thick layer of inedible gristle, which makes preying on them a lot of work. While sharks, orcas and sea lions will occasionally eat them, they typically do so only during times of food stress. Sea lions, for example, resorted to hunting Mola molas during warm-water events in 2015 and 2016 that diminished forage fish populations off the California coast. The sea lions would shake the hapless molas at the surface, ripping open their vulnerable underbellies. The pinnipeds would then eat just the meat and organs they could easily access and then leave the majority of the expired mola to sink slowly into the blue.

Approaching a mola is easiest when it's at an active cleaning station — divers can sometimes get within a few feet of them. Very large free-swimming molas in the open sea may also be approachable. The challenge can be getting in front of the animal for some face time and not getting stuck photographing its back end as it swims away. The key is a slow, calm approach — molas will leave if they perceive signs of aggression.

The absolute craziest Mola mola event I ever witnessed was the appearance in the mid-1990s of thousands of them seemingly everywhere off the coast of San Diego, Calif. My buddy and I pulled up to a drifting kelp paddy, jumped in the water and were shocked to see close to 50 adult molas swimming around us. Most were being cleaned by halfmoon fish and did not care about our presence. We have never again seen as many as we did that year, but we keep heading offshore just in case.

Bali’s Mola Diving
By Douglas Seifert

Between July and October at a few deep and current-swept sites off Bali's satellite islands, thousands of divers seek encounters with one of the oddest fish in the sea: the ocean sunfish, or mola.

Although the ocean sunfish is related to the pufferfish, boxfish and triggerfish, it is like no other. It lacks a swim bladder, having instead an incompressible, gelatinous, subcutaneous tissue that can make up as much as 44 percent of its mass. This tissue along with the animal's skin, which can be up to 8 inches thick in larger molas, render it neutrally buoyant at any depth.

The sunfish is the most fecund fish in the ocean; one 4-foot-long female was found to have 300 million eggs in its ovaries. By the time an egg becomes a full adult, the fish will have increased in weight 60 million times.

Although many English speakers refer to it as a sunfish, it's known in some other European languages as a moonfish. Its family name, Molidae, and genus name, Mola, are derived from the Latin word for millstone, as its physique is reminiscent of a large disc. But it looks much more like a swimming head with a conspicuously tall dorsal fin, a long anal fin and no discernable tail. A pseudotail, called a clavus, functions more or less as a rudder, but all the swimming power comes from the synchronized beating of its two large fins. The fins are even powerful enough to enable the sunfish to breach the water's surface and briefly launch itself into the air — no mean feat for the largest bony fish in the sea.

In addition to an unusual shape, sunfish have large eyes and large, puckered mouths, which they are physically unable to close completely. Their bizarre appearance and great size (they can measure more than 10 feet from fin tip to fin tip) and the fact that they're not encountered very often have made them a bucket-list attraction for many divers who visit Bali.

Bali has several seasonal sites at which divers can encounter molas that come to be cleaned of parasites. The dives are often deep and current-swept, so these encounters are best suited to advanced divers.

The reason sunfish are not often encountered is that their preferred habitat is the pelagic realm of open ocean and deep water. They feed wherever jellyfish are most abundant, and this means they're often far from sport-diving sites. They are sometimes seen at the surface, warming themselves after forays into the chilly depths. These predatory forays into the deep expose sunfish to the many parasites that prey on them and thus eventually lead the fish to the cleaning stations at which divers find them.

Bali's pioneering dive operations discovered many cleaning stations in the 1980s and 1990s, and word has spread. Now hordes of divers from around the world descend on Crystal Bay, Blue Corner, Toyapakeh and other sites with active cleaning stations for five months each year.

The sunfish season is the result of a seasonal upwelling driven by the southeast monsoon. The monsoon brings cold water and the molas that inhabit it into proximity with the warm tropical water that supports the coral reef cleaning-station fishes. But the thermocline where these waters meet is often quite deep (130 feet or more), and the water below it can be very cold (63°F or even colder). As if the depth and temperature were not enough, many of these sites lie at the frontiers of extremely powerful currents, including downdraft currents, that have caused the deaths of divers.

On really crowded days 100 divers might be searching for sunfish at Bali's deep cleaning stations and jockeying for position within a relatively small area. There is a code of conduct that's meant to prevent undue disturbance of the fish, but compliance is voluntary, and overzealous or selfish divers sometimes spook them.

Much about sunfish is still unknown. It was only recently determined that the fish found on Bali's cleaning stations are not the cosmopolitan ocean sunfish, Mola mola, but rather the southern sunfish, Mola ramsayi. A photo identification research project is under way in Bali, and preliminary findings suggest that the sunfish there are resident year-round but are only seen during mola season, when the water temperature brings them into sport-diving depths.
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Watch cleaner fish and seagulls help remove parasites from Mola molas in this video.

© Alert Diver — Q3 Summer 2017