Ocean Sunfish (Mola) (Mola mola)

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Overview

The ocean sunfish (Mola mola) is one of the strangest fish in the sea — a huge, flattened, almost circular fish that looks like a giant swimming head. It has tall dorsal and anal fins, no real tail (instead a rounded rudder-like structure called a clavus), and a tough, leathery skin. The ocean sunfish is the heaviest bony fish in the world, with the largest individuals weighing well over a tonne.

Despite its enormous size, the mola is a gentle, slow-moving drifter, often seen lying on its side at the surface as if sunbathing — the behaviour behind its name.

Note: a couple of closely related giant sunfish exist; details here use Mola mola. Treat general statements as approximate and verify against authoritative sources.

Habitat & Range

Ocean sunfish live in temperate and tropical oceans worldwide, ranging through the open sea from the surface down into deep, cold water. They often come up to bask at the surface, but they also dive deep to feed, moving between warm upper waters and the chilly depths.

Diet

Ocean sunfish were long thought to feed mainly on jellyfish and other gelatinous animals, and these do form a large part of the diet; however, studies show molas also eat a varied menu including small fish, crustaceans, squid, and seafloor invertebrates. Because jelly-like prey is low in nutrients, the sunfish must eat a great deal to sustain its huge body.

Behavior

The ocean sunfish swims by sculling its tall dorsal and anal fins from side to side, an unusual style for such a large fish, and steers with the clavus. It is famous for basking flat at the surface, which may help it warm up after deep, cold-water dives and may let seabirds and other fish pick off its many skin parasites. Sunfish are extraordinarily fecund — a large female can carry an enormous number of tiny eggs — yet only a few survive to adulthood.

Human Interaction & Conservation

Ocean sunfish are harmless to people and a favourite sight for divers and boaters. They are caught (sometimes as bycatch) and eaten in some regions, and they can be harmed by floating plastic, which resembles their jellyfish prey, and by entanglement in fishing gear. Their conservation status varies by region. Consult NOAA Fisheries and the IUCN Red List for current status.

More photos of the ocean sunfish (mola)