New research shows that they forage for marine hydrozoans (Greek for sea serpent), which are small groups of predatory animals related to jellyfish. The fish take siphonophores, a type of hydozoan, most frequently at depths of between 50-200m. After their hunt they go back to the surface to top up their body temperatures by basking in the sun.

It's the first evidence that sunfish graze on these creatures in deep water. It was also previously believed they only ate jellyfish.