Ocean Sunfish
A 2,000-pound fish that looks like a swimming head with fins bolted on
No photo available for Ocean Sunfish
The wacky thing
The ocean sunfish (Mola mola) has no real tail. Instead of a tapered body, it looks like it's just a massive disc-shaped head — the tail fin is replaced by a rudder-like structure called a clavus, formed from fused fin rays. It's the heaviest bony fish in the world, regularly exceeding 1,000 kg, and it swims by flapping its dorsal and anal fins side to side like wings.
Overview
Mola mola drift and swim slowly through temperate and tropical oceans worldwide, feeding mostly on jellyfish and other soft-bodied drifters — a diet so low in calories that adults have to eat enormous volumes constantly to sustain their size. They're famous for basking sideways at the surface, apparently to let sunlight warm them after deep dives into cold water and to invite seabirds to pick parasites off their skin.
Found in
Temperate and tropical oceans worldwide, from the surface down to depths over 600 meters during feeding dives.
Things worth knowing
- 1
A single ocean sunfish can produce around 300 million eggs in one spawning event — more than any other known vertebrate.
- 2
Despite their bulk, sunfish are surprisingly athletic divers, regularly plunging hundreds of meters into cold water to feed on deep-sea jellyfish, then returning to the surface to bask and rewarm.
- 3
Their skin can be up to 7.5cm thick and is covered in mucus and a dense layer of parasites — a single sunfish has been recorded hosting over 40 species of parasites, more than any other fish.
- 4
The name 'sunfish' comes from their basking behavior; the genus name Mola is Latin for 'millstone,' describing their rounded, grey, rough-skinned shape.
- 5
Ocean sunfish can grow explosively fast, gaining around 400kg in about 15 months in captivity — among the fastest growth rates of any vertebrate.