The ocean sunfish, or mola mola, is an unusual shape. Indeed, his Latin name "mola" means millstone, reflecting his roundish appearance. This sunfish belongs to the "molidae" family, which has three members: the slender mola, the sharp-tailed mola and the round-tailed or common mola. The latter is the most abundant, and his tendency to float on the ocean as if he's sunbathing earned him the name "ocean sunfish."
The mola owes his rounded, bullet-like shape to the fact that his back fin doesn't develop after birth. Instead it folds inwards to form a circular rudder called a clavus. He is the heaviest of all the bony fish species, and some specimens can weigh up to 5,000 pounds. He can measure up to 14 feet in length and 10 feet across, making him almost as wide as he's long. The mola has a large dorsal fin, which observers sometimes mistake for that of a shark when he surfaces to sunbathe on the ocean's surface. He has a small mouth, considering his size, and his teeth are fused together to form a beak-like structure. His skin is silvery, rough-textured and covered with lots of mucus.
Breeding and Environment
A female mola can lay around 300 million eggs in one season, more than any other vertebrate. The male fertilizes them externally; however, most of these are eaten by predators and a mere 1 percent develop into baby mola, called fry. A baby mola has spikes like his puffer fish relative, but these fall off as he grows. Mola youngsters stay together in schools for protection from predators.
Little information is available about the longevity of a mola in the wild, but they're known to live up to 10 years in captivity. However, BioExpedition says it's difficult to create a hospitable captive environment for the mola and that he's certainly not a home aquarium fish. The mola needs a saltwater habitat in tropical and temperate waters of about 50 degrees Fahrenheit, and you find mola populations in all parts of the world where the water is warm enough for him.
The omnivorous mola likes eating gelatinous zooplankton such as jellyfish and Portuguese man-o-war. He also eats squid, sponges, deep-water eel larvae, small fishes, eel grass and some crustaceans. Examination of his diet shows that he forages for food at the ocean's surface and among floating weeds, as well as on the sea bed and in deep water.
Parasites and Predators
The ocean sunfish's skin is a notorious host for parasites. He frequently relies on small fish and birds -- when he's basking at the surface -- to feed on these parasites, and he's known to breach the water's surface, leaping to a height of 10 feet, in an attempt to shake the parasites off. One parasite living on him is the shark tapeworm larva. The Ocean Sunfish website say this indicates that sharks must eat sunfish so the shark tapeworm can complete its life cycle. Some 40 types of parasites have been found living on ocean sunfish, and even the parasites have parasites.
Sea lions and orcas are his main predators, but he also falls prey to humans. Ocean Sunfish reports that the mola is a main "bycatch" of drift-net fishing for swordfish off the U.S. Pacific coast, and that mola account for 42 percent of the fishermen's discards.
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Based in London, Eleanor McKenzie has been writing lifestyle-related books and articles since 1998. Her articles have appeared in the "Palm Beach Times" and she is the author of numerous books published by Hamlyn U.K., including "Healing Reiki" and "Pilates System." She holds a Master of Arts in informational studies from London University.