Ocean sunfish

The heaviest bony fish in the world

The sunfish looks like a giant swimming disc with a head: no tail, a flat round body. It weighs up to 2 tonnes — like a small car! It eats jellyfish and floats on its side at the surface to 'sunbathe', while birds pick parasites off its skin. It is born as a tiny speck — one of 300 million eggs.

The ocean sunfish (Mola mola) is the heaviest bony fish (record 2,300 kg, 3.3 m), found in all temperate and tropical oceans. It has no tail fin — it rows with its dorsal and anal fins, with a 'clavus' in place of a tail. Its skin is 7 cm thick and coated in mucus. Diet: jellyfish, comb jellies, small squid. By day it dives to 600 m, then basks on its side at the surface (thermoregulation) while birds and cleaner fish remove parasites (over 40 species). A female lays 300 million eggs — a vertebrate record; the 2.5 mm larva grows 60 million-fold. Accidental capture in nets makes it IUCN Vulnerable.

Fun facts

• A sunfish lays 300 million eggs — a vertebrate record.
• It grows 60 million times bigger than at birth.
• It has no tail — it rows with its fins like oars.