Ocean Sunfish

The ocean sunfish is the world's heaviest bony fish, a strange, flattened giant that looks like a swimming head drifting through the open sea.

Also known as: common sunfish, giant sunfish, headfish, mola mola, mola ocean sunfish, moonfish, sun-fish, sunfish

An adult ocean sunfish is unlikely to be confused with any other fish once seen side-on, thanks to its flattened, tail-less disc shape. The only real confusion happens with newly hatched young, which look like tiny, spiky pufferfish rather than smooth adult sunfish.

The ocean sunfish has a beak-like mouth formed from four fused teeth, a trait it shares with pufferfish and other relatives in its order. Instead of a normal tail fin, it has a rounded, frilled edge called a clavus, giving the whole body a truncated, cut-off look. The body is flattened from side to side into a long oval shape when viewed head-on, with small, fan-shaped pectoral fins and a long dorsal fin and anal fin that often make the fish about as tall as it is long. It can grow to about 3.3 m in height and weigh up to 2,300 kg.

Ocean sunfish live in temperate and tropical waters across every ocean, in water between about 12 and 25 degrees Celsius. Although often thought of as surface baskers, adults spend much of their time hunting at depth, diving as deep as 480 m, though they usually stay between about 30 and 70 m.

Ocean sunfish are sometimes seen lying on their side at the surface, presenting their largest side to the sun, a behaviour thought to help them warm back up after hunting in cold, deep water. Their great size and thick skin protect adults from most predators, though orcas, large sharks, and sea lions will still take them; younger sunfish are more vulnerable, and can fall prey to tuna and mahi-mahi.

Once thought to feed mainly on jellyfish, the ocean sunfish is now known to be a generalist predator, eating mostly small fish, fish larvae, squid, other molluscs, and crustaceans, with jellyfish making up only a modest part of the diet. It hunts at many depths, from near the surface down to the seafloor in some areas.

harmless to humans

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  Bump-head Mola

  Mola alexandrini