Animal · United States, Mexico, Portugal
Ocean sunfish
Mola mola — the name this animal has in the language scientists everywhere share.
The ocean sunfish looks like a huge swimming head, because its body ends just behind the two tall fins it rows through the water with. It is the heaviest bony fish in the sea.
Picture credit: National Marine Sanctuaries (Public domain) · Nol Aders (CC BY 2.5) · Wikimedia Commons
Where does the ocean sunfish live?
Home: Open ocean in warm and mild seas.
In the wild it lives in these countries: the United States, Mexico, Portugal, Spain, Japan, Australia, New Zealand, South Africa.
Conservation status from the IUCN: vulnerable.
The short profile
Fully grown: up to about 3 metres from fin tip to fin tip. It weighs about 1 000 kilograms. On the menu: meat.
The story behind it
A grown sunfish can weigh as much as a small car, yet it starts life as an egg smaller than a grain of sand. A female can release up to about 300 million eggs at a time, more than any other animal with a backbone. The young are round and covered in spines, and they grow millions of times heavier before they are adult. Instead of a normal tail the sunfish has a stiff frill called a clavus, and it steers by beating its top and bottom fins like slow wings. It dives hundreds of metres into cold water to feed on small fish, squid, salps and jellyfish, then comes back up and lies on its side at the surface to warm again. Gulls and small cleaner fish pick parasites off its thick, rubbery skin, and more than forty kinds of parasite have been found on a single fish. Sunfish are often caught by accident in drifting nets, which is why they count as vulnerable.
Find it on the globe
Ocean sunfish is there as a tiny animated figure that breathes and looks around. From far away the planet is only a blue ball; detail arrives as you zoom in, and this one appears once you are close enough. Open it on the globe.
It sits at its real coordinates, not near them — the same numbers listed in the facts above. Switch off the layer for this kind of place and it disappears again; the buttons for that are down the right-hand edge.
Questions children ask
Why does it lie on its side at the surface?
After a long, cold dive it has to warm up again, and the sun on its broad flank does that quickly. Seabirds use the chance to pick parasites off its skin.
What is inside its mouth?
Its mouth never closes fully, and the front teeth are grown together into a hard beak. Further back sit rough plates in the throat that mash soft, slippery food before it is swallowed.
Are sunfish dangerous to people?
No. They have no sting and no biting teeth, and they take almost no notice of swimmers, so divers can often come quite close. The danger runs the other way, from boats and nets.
Where these numbers come from
Every figure on this page was checked against public reference sources before publication. Where sources genuinely disagree, the text says so.
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