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Bizarre basker

Jan 1, 2003

When the cement-transporter MV Goliath docked at Sydney, Australia, on Oct. 13, 1998, onlookers discovered that it was carrying a curious cargo. Underwater on its bulbous bow was lodged a 3,000-lb fish. The animal had become inadvertently stuck there while the ship was traveling off Jervis Bay, New South Wales.

At the wharf, the Sydney Waterways Authority came to the ship's aid and hauled off the odd-looking, gigantic creature. When scientists from the Australian Museum arrived on the scene to document the specimen, they measured it at more than 8 feet long and 10 feet tall from fin tip to fin tip.

ýThis peculiar sea monster was an ocean sunfish, also known as a mola, the heaviest bony fish in the world. On its website, the Monterey Bay Aquarium describes the species as: “All head and no tail, ocean sunfish look something like big, leathery Frisbees. They scull along by flapping their big top and bottom fins, using their stumpy tails to steer.”

Although ultimately it had perished en route to Sydney, the Aussie sunfish had waged a respectable battle with Goliath. The fish's sheer bulk had slowed the cement-carrier from 14 to 11 knots, and its rugged, abrasive skin had burnished the painted hull to bare metal. Indeed, in this showdown it's difficult to say whether the sunfish or MV Goliath, itself, was David or Goliath.

As this incident demonstrates, the ocean sunfish can pose a formidable hazard to navigation. The impact of striking one of the massive finned beasts in a sailboat could be comparable to colliding with a whale or with a half-submerged container lost overboard from a cargo ship. Found worldwide

Such piscine collisions are entirely possible, because giant sunfish inhabit oceans around the world. Their total population size is not known, but they are reasonably abundant and range in all temperate and tropical oceans, both offshore and in coastal waters. The animals habitually lounge at the ocean's surface for long periods, and they can be so languorous that they -o not move away when approached by a boat.

While the chances of actually colliding with an ocean sunfish may be slim, the odds of observing one up close are good. Indeed, the ocean sunfish is primarily significant to sailors, not as a floating obstacle but as one of the most fascinating, bizarre and approachable large, wild creatures of the sea.

The ocean sunfish, or mola, is a member of the family Molidae, along with three similar but smaller species. It is a completely different beast from the small, freshwater sunfish familiar to lake fishermen. Swimming or basking with its dorsal fin swaying in the air, the ocean sunfish often is mistaken from a distance for a shark. Typically the above-water fin of a mola can be distinguished from a shark's because it wobbles from side to side, rather than remaining fairly rigid and moving forward like a shark's.

The common name of “sunfish” reflects the animal's habit of basking; warming its body in the sun may help the fish speed its digestive process. The ocean sunfish's scientific name Mola mola means “millstone,” a reference to its body shape. Likewise, in German the fish is nicknamed chwimmenderkopf, or “swimming head.”

In the Atlantic Ocean, the mola can be found as far north as Scandinavia and Newfoundland and south to Argentina and South Africa. It is sometimes observed in the Mediterranean and the western Baltic Sea. In the Pacific Ocean, the species ranges from the latitude of British Columbia to Peru and Chile. Some people have suggested that global warming may be causing the ocean sunfish to increase its numbers in northern waters, such as the British Isles.A surfboard with wings

The ocean sunfish's thin body is roughly rectangular and has been described as a gray surfboard with wings. Lacking a conventional fish tail, the back end is a blunt, frilled and broadly curved edge. The astonishingly long and wing-like dorsal and anal fins point up and down, not horizontally like an airplane's wings. Their total height rivals the overall length of the fish.

Nearly everything else about the body looks similarly disproportioned. The pectoral fins are stubby. The head dominates a third of the total body length. The comically O-shaped small mouth has its teeth fused into a beak, like a parrot. The eyes are set approximately halfway between the mouth and pectoral fin. (One first-time observer of an ocean sunfish recalled her surprise at the eyes' largeness and their resemblance to a mammal's.)

Despite its ungainly appearance, the mola can swim with remarkable grace and speed. Propelling itself by fluttering its dorsal and anal fins, the fish may zoom away when disturbed or to feed, diving as deep as 1,800 feet. Ocean sunfish even have been seen jumping above the ocean surface, sometimes in schools of a dozen.

When it basks, the sunfish often lies nearly motionless on its side, like a floating grayish disc. Or it may swim upright near the surface, with its dorsal fin extending above water. Some ocean sunfish are so passive that they can be grabbed alive and hýuled aboard a boat (as one researcher has done to study the parasites living on the fish's skin). According to tales, children in the tropics even climb onto and walk around on basking sunfish, as if they were rafts. (Liability disclaimer: Don't try this at home or at sea.)

The mighty sunfish begins life as a tiny larva only one-tenth of an inch long. The species is extraordinarily fecund and has been listed in the Guinness Book of World Records as the fish carrying the most eggs. Inside one small 4-foot female, scientists discovered more than 300 million eggs, exceeding the usual number of eggs in other fish by a factor of between six and 15.

Unlike the adult, the larva is boxy and features a tail fin, body spines and prominent pectoral fins traits that cause it to resemble some of the mola's closest relatives, the puffer fish and boxfish.Growth champ

As it grows into adult form and potentially attains a maximum length exceeding 10 feet, the mola can increase its weight over its lifetime by 60-million fold. Calling the species the “growth champion among animals,” ichthyologist E.W. Gudger calculated that a larva transforming into an adult mola would be equivalent to a 150-lb rowboat growing into a vessel that weighed 60 times as much as RMS Queen Mary. (Queen Mary weighed 80,773 tons.)

ýDespite their enormous size, ocean sunfish have small mouths and are harmless to people. They feed on jellyfish, zooplankton, crustaceans, smaller fish and algae. In a National Geographic Society report, zoologist Tierney Thys noted in what she called a “cosmic convergence” that the favorite food of the ocean sunfish is the moon jellyfish.

Given its size and apparent defenselessness, the ocean sunfish might seem an appealing target for fishermen and hungry sailors. Yet, although historical records do indicate that Aran Islanders once harpooned the fish and some people still consider it a delicacy, the mola is rarely eaten. One possible reason for the ocean sunfish's culinary unpopularity is a toxin in its body that reputedly can be similar in potency to the deadly poison of puffer fish and porcupine fish.

The few predators that do consume the ocean sunfish include sharks, killer whales and sea lions. To compensate for its vulnerable, lazy habits and to avoid becoming an easy meal, the ocean sunfish armors itself with exceptionally tough, resilient skin that acts like a bulletproof vest. Composed of densely woven collagen fibers, the skin is elastic and can be 6 inches thick. According to Thys, fishermen's children in the 1800s wrapped chunks of mola skin with twine to make “bouncy balls.”

Regardless of their protective skin, some ocean sunfish do succumb to predators. When schools of young, three-foot-long ocean sunfish arrive during the summer with the balmy currents flowing into Monterey Bay in California, they are attacked by ravenous sea lions. “The sea lions tear off a mola's dorsal and anal fins and slam the helpless fish against the water's surface,” according to Thys. “If they fail to rip through its tough skin, the sea lions may toss the crippled mola about like a giant Frisbee and finally abandon it to voracious seagulls.”

Under more ordinary circumstances, however, a mola may actually invite seabirds to feed on its body or, more precisely, on the parasites infesting its thick skin. Forty different species of parasites dwell in and on the skin, numbering in the thousands on a single sunfish. One researcher counted more than a hundred individuals of a single species the tiny crab-like copepod of the species Lepeophtheirus nordmanni parasitizing a small ocean sunfish only 3 feet in diameter.

The sunfish tolerates these cleanings by birds and smaller fish apparently because they help to reduce infestation by parasites. In Southern California, ocean sunfish gather in great numbers in kelp forests to be cleaned by small fish that live there. And as molas bask on the ocean surface, they often seem to welcome the seabirds that climb aboard to peck their skin for meals of parasites.

Flocks of herring gulls and other birds can signal the presence of basking ocean sunfish. But if the gulls become too insistent, the sunfish may lunge and squirt water at them. Keeping in mind the damage the Aussie ocean sunfish inflicted on the cement-transport ship, those seagulls would be well advised to wing safely away and leave sunfish watching to those alert ocean sailors who chance to spot these odd-looking animals.

¬Pete Taylor is a freelance writer and editor who lives in Portland, Maine. He earned a graduate degree in marine ecology from the University of California, Santa Barbara.